报告仓库：dekrt/Reports: HUST SSE Courses Reports | 华科软件学院课程报告 (github.com)

软件设计综合实践实验报告

1. 实验内容和要求

本实验通过一个类 C 语言的 C--（C Minus Minus，CMM）语言编译器的设计和实现来熟悉编译器的基本原理和概念，了解计算系统基本架构（机器硬件层抽象、 目标语言、语言编译和汇编语言等），熟练掌握 C 语言开发，并为后续课程的学习打下基础。

2. 斐波拉契数代码

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int fibonacci(int n)
{
    int cnt;
    int firstFib;
    int secondFib;
    int fib;

    firstFib = 1;
    secondFib = 1;
    cnt = 2; /* n = 1 或 n = 2 时特判 */

    if (n == 1)
        return 1;
    else if (n == 2)
        return 1;
    else
    {
        while (cnt < n)
        {
            fib = firstFib + secondFib;
            firstFib = secondFib;
            secondFib = fib;
            cnt = cnt + 1;
        }
    }
    return fib;
}

void main(void)
{
    int n;
    n = input();
    output(fibonacci(n));
}

3. 词法分析程序

3.1 主要设计和实现思路

采用enum进行状态码的描述，具体如下：

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typedef enum
{
  START,        // 开始状态
  INNUM,    	// 输入数字
  INID,     	// 输入identifier
  INEQ,     	// 第一次输入 = , 可能是  = 或 ==
  INLT,     	// 输入 < , 
  INGT,     	// 输入 >
  INDIV,    	// 输入 / 
  INNE,    		// 输入 !
  INCOMMENT,    // 输入 /*
  ENDCOMMENT,   // 输入 */
  DONE			// 结束状态
} StateType;

struct reservedWords结构用来存储预置词

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static struct
{
  char *str;
  TokenType tok;
} reservedWords[MAXRESERVED] = {{(char *)"if", IF}, {(char *)"else", ELSE}, 
                                {(char *)"while", WHILE}, {(char *)"int", INT}, 
                                {(char *)"void", VOID}, {(char *)"return", RETURN}};

static int getNextChar(void) 与 static int ungetNextChar(void)函数用于读取下个字符与回溯下个字符

TokenType getToken(void) 函数用于获取当前的token：

  • 如果状态码是START，进行一次getNextChar()：
    • 对于一元操作符，如'+', '-', '*', '(', ')', ';', '{', '}'等字符，直接给出currentToken
    • 对于可能存在的二元（多元）操作符，如"= || ==", "< || <=", "> || >=", "! || !=", "/ || /*"等状态，给定对应的状态码，进行进行进一步的判断
    • break；
  • 如果状态码是INEQ，则读取字符并判断是=还是==
  • 如果状态码是INLT，则读取字符并判断是<还是<=
  • 如果状态码是INGT，则读取字符并判断是>还是>=
  • 如果状态码是INNE，则读取字符并判断是!还是!=
  • 如果状态码是INDIV，则读取字符并判断是/*还是/*
    • 为了防止注释中可能的*进行干扰，采用INCOMMENT和ENDCOMMENT两种状态进行判断
  • 如果状态码是INNUM或者INID，则进行读取
  • 否则，输出错误信息
  • 随后，对新的ID进行存储。
  • 如果TraceScan == true ，则调用UTIL.c中的printToken()函数，输出词法分析的结果
  • 返回当前的Token

调用printToken()函数进行token的打印，函数如下：

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void printToken(TokenType token, const char* lexeme)
{
    switch(token)
    {
        case IF:
        case ELSE:
        case INT:
        case RETURN:
        case VOID:
        case WHILE:
        	fprintf(listing, "reserved word \"%s\"", lexeme);
        	break;
        case PLUS:    fprintf(listing, "+"); break;
        case MINUS:   fprintf(listing, "-"); break;
        case TIMES:   fprintf(listing, "*"); break;
        case DIVIDE:  fprintf(listing, "/"); break;
        case LT:      fprintf(listing, "<"); break;
        case GT:      fprintf(listing, ">"); break;
        case ASSIGN:  fprintf(listing, "="); break;
        case NE:      fprintf(listing, "!="); break;
        case SEMI:    fprintf(listing, ";"); break;
        case COMMA:   fprintf(listing, ","); break;
        case LPAREN:  fprintf(listing, "("); break;
        case RPAREN:  fprintf(listing, ")"); break;
        case LBRACE:  fprintf(listing, "{"); break;
        case RBRACE:  fprintf(listing, "}"); break;
        case LSQUARE: fprintf(listing, "["); break;
        case RSQUARE: fprintf(listing, "]"); break;
        case LTE:     fprintf(listing, "<="); break;
        case GTE:     fprintf(listing, ">="); break;
        case EQ:      fprintf(listing, "=="); break;
        case NUM:
        	fprintf(listing, "NUM, value = %s", lexeme);
        	break;
        case ID:
        	fprintf(listing, "ID, name = \"%s\"", lexeme);
        	break;
        case ENDOFFILE:
        	fprintf(listing, "EOF");
        	break;
        case ERROR:
        	fprintf(listing, "<<<ERROR>>> %s", lexeme);
        	break;
        default: 
        	fprintf(listing, "<<<UNKNOWN TOKEN>>> %d", token);
    }
}

3.2 词法分析程序代码

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#include "globals.h"
#include "util.h"
#include "scan.h"

/* states in scanner DFA */
typedef enum
{
  START,
  INNUM,    // input number
  INID,     // input identifier
  INEQ,     // input = , maybe = or ==
  INLT,     // input < , 
  INGT,     // input >
  INDIV,     // input / 
  INNE,     // input !
  INCOMMENT,     // input /*
  ENDCOMMENT,     // input */
  DONE
} StateType;

/* lexeme of identifier or reserved word */
char tokenString[MAXTOKENLEN + 1];

/* BUFLEN = length of the input buffer for
   source code lines */
#define BUFLEN 256

static char lineBuf[BUFLEN]; /* holds the current line */
static int linepos = 0;      /* current position in LineBuf */
static int bufsize = 0;      /* current size of buffer string */
static int EOF_flag = FALSE; /* corrects ungetNextChar behavior on EOF */

/* getNextChar fetches the next non-blank character
   from lineBuf, reading in a new line if lineBuf is
   exhausted */
static int getNextChar(void)
{
  if (!(linepos < bufsize))
  {
    lineno++;
    if (fgets(lineBuf, BUFLEN - 1, source))
    {
      if (EchoSource)
        fprintf(listing, "%4d: %s", lineno, lineBuf);
      bufsize = strlen(lineBuf);
      linepos = 0;
      return lineBuf[linepos++];
    }
    else
    {
      EOF_flag = TRUE;
      return EOF;
    }
  }
  else
    return lineBuf[linepos++];
}

/* ungetNextChar backtracks one character
   in lineBuf */
static void ungetNextChar(void)
{
  if (!EOF_flag)
    linepos--;
}

/* lookup table of reserved words */
static struct
{
  char *str;
  TokenType tok;
} reservedWords[MAXRESERVED] = {{(char *)"if", IF}, {(char *)"else", ELSE}, 
                                {(char *)"while", WHILE}, {(char *)"int", INT}, 
                                {(char *)"void", VOID}, {(char *)"return", RETURN}};

/* lookup an identifier to see if it is a reserved word */
/* uses linear search */
static TokenType reservedLookup(char *s)
{
  int i;
  for (i = 0; i < MAXRESERVED; i++)
    if (!strcmp(s, reservedWords[i].str))
      return reservedWords[i].tok;
  return ID;
}

/****************************************/
/* the primary function of the scanner  */
/****************************************/
/* function getToken returns the
 * next token in source file
 */
TokenType getToken(void)
{ /* index for storing into tokenString */
  int tokenStringIndex = 0;
  /* holds current token to be returned */
  TokenType currentToken;
  /* current state - always begins at START */
  StateType state = START;
  /* flag to indicate save to tokenString */
  int save;
  while (state != DONE)
  {
    int c = getNextChar();
    save = TRUE;
    switch (state)
    {
    case START:
      if (isdigit(c))
        state = INNUM;
      else if (isalpha(c))
        state = INID;
      else if (c == '=')
        state = INEQ;
      else if (c == '<')    
        state = INLT;
      else if (c == '>')
        state = INGT;
      else if (c == '!')
        state = INNE;
      else if (c == '/')
        state = INDIV;
      else if ((c == ' ') || (c == '\t') || (c == '\n'))
        save = FALSE;
      else
      {
        state = DONE;
        switch (c)
        {
          case EOF:
            save = FALSE;
            currentToken = ENDFILE;
            break;
          case '+':
            currentToken = PLUS;
            break;
          case '-':
            currentToken = MINUS;
            break;
          case '*':
            currentToken = TIMES;
            break;
          case '(':
            currentToken = LPAREN;
            break;
          case ')':
            currentToken = RPAREN;
            break;
          case ';':
            currentToken = SEMI;
            break;
          case '{':
            currentToken = LBRACE;
            break;
          case '}':
            currentToken = RBRACE;
            break;
          default:
            currentToken = ERROR;
            break;
        }
      }
      break;

    case INEQ:
      state = DONE;
      if (c == '=')
        currentToken = EQ;
      else
      { /* backup in the input */
        ungetNextChar();
        save = FALSE;
        currentToken = ASSIGN;
      }
      break;
    case INLT:
      state = DONE;
      if (c == '=')
        currentToken = LTE;
      else
      {
        ungetNextChar();
        save = FALSE;
        currentToken = LT;
      }
      break;
    case INGT:
      state = DONE;
      if (c == '=')
        currentToken = GTE;
      else
      {
        ungetNextChar();
        save = FALSE;
        currentToken = GT;
      }
      break;
    case INNE: 
      state = DONE;
      if (c == '=')
        currentToken = NEQ;
      else
      {
        ungetNextChar();
        save = FALSE;
        currentToken = ERROR;
      }
      break;
    case INDIV:
      if (c == '*')
      {
        save = FALSE;
        state = INCOMMENT;
        tokenStringIndex -= 1;
      }
      else
      {
        ungetNextChar();
        save = FALSE;
			  state = DONE;
			  currentToken = DIVIDE;
      }
      break;

    case INCOMMENT:
      save = FALSE;
      if(c == '*')
        state = ENDCOMMENT; 
      break;

    case ENDCOMMENT:
      save = FALSE;
      if (c == '/')
        state = START;
      else if (c == '*')
        state = ENDCOMMENT;
      else
        state = INCOMMENT;
      break;

    case INNUM:
      if (!isdigit(c))
      { /* backup in the input */
        ungetNextChar();
        save = FALSE;
        state = DONE;
        currentToken = NUM;
      }
      break;
    case INID:
      if (!isalpha(c))
      { /* backup in the input */
        ungetNextChar();
        save = FALSE;
        state = DONE;
        currentToken = ID;
      }
      break;
    case DONE:
    default: /* should never happen */
      fprintf(listing, "Scanner Bug: state= %d\n", state);
      state = DONE;
      currentToken = ERROR;
      break;
    }
    // append new id to token string
    if ((save) && (tokenStringIndex <= MAXTOKENLEN))
      tokenString[tokenStringIndex++] = (char)c;
    if (state == DONE)
    {
      tokenString[tokenStringIndex] = '\0';
      if (currentToken == ID)
        currentToken = reservedLookup(tokenString);
    }
  }
  if (TraceScan)
  {
    fprintf(listing, "\t%d: ", lineno);
    printToken(currentToken, tokenString);
  }
  return currentToken;
} /* end getToken */

3.3 实验演示

  • 求三个整数中的最大值
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in Line:  2: get reserved word "int"
in Line:  2: get ID, name = "max"
in Line:  2: get (
in Line:  2: get reserved word "int"
in Line:  2: get ID, name = "x"
in Line:  2: get ,
in Line:  2: get reserved word "int"
in Line:  2: get ID, name = "y"
in Line:  2: get ,
in Line:  2: get reserved word "int"
in Line:  2: get ID, name = "z"
in Line:  2: get )
in Line:  3: get {
in Line:  4: get reserved word "int"
in Line:  4: get ID, name = "biggest"
in Line:  4: get ;
in Line:  5: get ID, name = "biggest"
in Line:  5: get =
in Line:  5: get ID, name = "x"
in Line:  5: get ;
in Line:  6: get reserved word "if"
in Line:  6: get (
in Line:  6: get ID, name = "y"
in Line:  6: get >
in Line:  6: get ID, name = "biggest"
in Line:  6: get )
in Line:  7: get ID, name = "biggest"
in Line:  7: get =
in Line:  7: get ID, name = "y"
in Line:  7: get ;
in Line:  8: get reserved word "if"
in Line:  8: get (
in Line:  8: get ID, name = "z"
in Line:  8: get >
in Line:  8: get ID, name = "biggest"
in Line:  8: get )
in Line:  9: get ID, name = "biggest"
in Line:  9: get =
in Line:  9: get ID, name = "z"
in Line:  9: get ;
in Line: 10: get reserved word "return"
in Line: 10: get ID, name = "biggest"
in Line: 10: get ;
in Line: 11: get }
in Line: 12: get reserved word "void"
in Line: 12: get ID, name = "main"
in Line: 12: get (
in Line: 12: get reserved word "void"
in Line: 12: get )
in Line: 13: get {
in Line: 14: get reserved word "int"
in Line: 14: get ID, name = "x"
in Line: 14: get ;
in Line: 15: get reserved word "int"
in Line: 15: get ID, name = "y"
in Line: 15: get ;
in Line: 16: get reserved word "int"
in Line: 16: get ID, name = "z"
in Line: 16: get ;
in Line: 17: get reserved word "int"
in Line: 17: get ID, name = "biggest"
in Line: 17: get ;
in Line: 18: get ID, name = "x"
in Line: 18: get =
in Line: 18: get ID, name = "input"
in Line: 18: get (
in Line: 18: get )
in Line: 18: get ;
in Line: 19: get ID, name = "y"
in Line: 19: get =
in Line: 19: get ID, name = "input"
in Line: 19: get (
in Line: 19: get )
in Line: 19: get ;
in Line: 20: get ID, name = "z"
in Line: 20: get =
in Line: 20: get ID, name = "input"
in Line: 20: get (
in Line: 20: get )
in Line: 20: get ;
in Line: 21: get ID, name = "biggest"
in Line: 21: get =
in Line: 21: get ID, name = "max"
in Line: 21: get (
in Line: 21: get ID, name = "x"
in Line: 21: get ,
in Line: 21: get ID, name = "y"
in Line: 21: get ,
in Line: 21: get ID, name = "z"
in Line: 21: get )
in Line: 21: get ;
in Line: 22: get ID, name = "output"
in Line: 22: get (
in Line: 22: get ID, name = "biggest"
in Line: 22: get )
in Line: 22: get ;
in Line: 23: get }
in Line: 24: get EOF
  • 给定 N，求 1 到 N 之和
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in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "sum"
in Line:  1: get (
in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "n"
in Line:  1: get )
in Line:  2: get {
in Line:  3: get reserved word "int"
in Line:  3: get ID, name = "result"
in Line:  3: get ;
in Line:  4: get reserved word "int"
in Line:  4: get ID, name = "i"
in Line:  4: get ;
in Line:  5: get ID, name = "i"
in Line:  5: get =
in Line:  5: get NUM, value = 1
in Line:  5: get ;
in Line:  6: get ID, name = "result"
in Line:  6: get =
in Line:  6: get NUM, value = 0
in Line:  6: get ;
in Line:  7: get reserved word "while"
in Line:  7: get (
in Line:  7: get ID, name = "i"
in Line:  7: get <=
in Line:  7: get ID, name = "n"
in Line:  7: get )
in Line:  8: get {
in Line:  9: get ID, name = "result"
in Line:  9: get =
in Line:  9: get ID, name = "result"
in Line:  9: get +
in Line:  9: get ID, name = "i"
in Line:  9: get ;
in Line: 10: get ID, name = "i"
in Line: 10: get =
in Line: 10: get ID, name = "i"
in Line: 10: get +
in Line: 10: get NUM, value = 1
in Line: 10: get ;
in Line: 11: get }
in Line: 12: get reserved word "return"
in Line: 12: get ID, name = "result"
in Line: 12: get ;
in Line: 13: get }
in Line: 15: get reserved word "void"
in Line: 15: get ID, name = "main"
in Line: 15: get (
in Line: 15: get reserved word "void"
in Line: 15: get )
in Line: 16: get {
in Line: 17: get reserved word "int"
in Line: 17: get ID, name = "n"
in Line: 17: get ;
in Line: 18: get reserved word "int"
in Line: 18: get ID, name = "s"
in Line: 18: get ;
in Line: 19: get ID, name = "n"
in Line: 19: get =
in Line: 19: get ID, name = "intput"
in Line: 19: get (
in Line: 19: get )
in Line: 19: get ;
in Line: 20: get ID, name = "s"
in Line: 20: get =
in Line: 20: get ID, name = "sum"
in Line: 20: get (
in Line: 20: get ID, name = "n"
in Line: 20: get )
in Line: 20: get ;
in Line: 21: get ID, name = "output"
in Line: 21: get (
in Line: 21: get ID, name = "s"
in Line: 21: get )
in Line: 21: get ;
in Line: 22: get }
in Line: 23: get EOF
  • 计算第n个斐波那契数
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in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "fibonacci"
in Line:  1: get (
in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "n"
in Line:  1: get )
in Line:  2: get {
in Line:  3: get reserved word "int"
in Line:  3: get ID, name = "cnt"
in Line:  3: get ;
in Line:  4: get reserved word "int"
in Line:  4: get ID, name = "firstFib"
in Line:  4: get ;
in Line:  5: get reserved word "int"
in Line:  5: get ID, name = "secondFib"
in Line:  5: get ;
in Line:  6: get reserved word "int"
in Line:  6: get ID, name = "fib"
in Line:  6: get ;
in Line:  8: get ID, name = "firstFib"
in Line:  8: get =
in Line:  8: get NUM, value = 1
in Line:  8: get ;
in Line:  9: get ID, name = "secondFib"
in Line:  9: get =
in Line:  9: get NUM, value = 1
in Line:  9: get ;
in Line: 10: get ID, name = "cnt"
in Line: 10: get =
in Line: 10: get NUM, value = 2
in Line: 10: get ;
in Line: 12: get reserved word "if"
in Line: 12: get (
in Line: 12: get ID, name = "n"
in Line: 12: get ==
in Line: 12: get NUM, value = 1
in Line: 12: get )
in Line: 13: get reserved word "return"
in Line: 13: get NUM, value = 1
in Line: 13: get ;
in Line: 14: get reserved word "else"
in Line: 14: get reserved word "if"
in Line: 14: get (
in Line: 14: get ID, name = "n"
in Line: 14: get ==
in Line: 14: get NUM, value = 2
in Line: 14: get )
in Line: 15: get reserved word "return"
in Line: 15: get NUM, value = 1
in Line: 15: get ;
in Line: 16: get reserved word "else"
in Line: 17: get {
in Line: 18: get reserved word "while"
in Line: 18: get (
in Line: 18: get ID, name = "cnt"
in Line: 18: get <
in Line: 18: get ID, name = "n"
in Line: 18: get )
in Line: 19: get {
in Line: 20: get ID, name = "fib"
in Line: 20: get =
in Line: 20: get ID, name = "firstFib"
in Line: 20: get +
in Line: 20: get ID, name = "secondFib"
in Line: 20: get ;
in Line: 21: get ID, name = "firstFib"
in Line: 21: get =
in Line: 21: get ID, name = "secondFib"
in Line: 21: get ;
in Line: 22: get ID, name = "secondFib"
in Line: 22: get =
in Line: 22: get ID, name = "fib"
in Line: 22: get ;
in Line: 23: get ID, name = "cnt"
in Line: 23: get =
in Line: 23: get ID, name = "cnt"
in Line: 23: get +
in Line: 23: get NUM, value = 1
in Line: 23: get ;
in Line: 24: get }
in Line: 25: get }
in Line: 26: get reserved word "return"
in Line: 26: get ID, name = "fib"
in Line: 26: get ;
in Line: 27: get }
in Line: 29: get reserved word "void"
in Line: 29: get ID, name = "main"
in Line: 29: get (
in Line: 29: get reserved word "void"
in Line: 29: get )
in Line: 30: get {
in Line: 31: get reserved word "int"
in Line: 31: get ID, name = "n"
in Line: 31: get ;
in Line: 32: get ID, name = "n"
in Line: 32: get =
in Line: 32: get ID, name = "input"
in Line: 32: get (
in Line: 32: get )
in Line: 32: get ;
in Line: 33: get ID, name = "output"
in Line: 33: get (
in Line: 33: get ID, name = "fibonacci"
in Line: 33: get (
in Line: 33: get ID, name = "n"
in Line: 33: get )
in Line: 33: get )
in Line: 33: get ;
in Line: 34: get }
in Line: 35: get EOF

4. Lex文件

4.1 Lex输入文件代码

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%{
#include "globals.h"
#include "util.h"
#include "scan.h"
/* lexeme of identifier or reserved word */
char tokenString[MAXTOKENLEN+1];
void printToken( TokenType token, const char* tokenString );
%}

digit       [0-9]
number      {digit}+
letter      [a-zA-Z]
identifier  {letter}+
newline     \n
whitespace  [ \t]+

%%

"if"            {return IF;}
"while"         {return WHILE;}
"else"          {return ELSE;}
"return"        {return RETURN;}
"int"           {return INT;}
"void"          {return VOID;}
"="             {return ASSIGN;}
"=="            {return EQ;}
"<"             {return LT;}
"<="            {return LTE;}
">"             {return GT;}
">="            {return GTE;}
"!="            {return NE;}
"+"             {return PLUS;}
"-"             {return MINUS;}
"*"             {return TIMES;}
"/"             {return DIVIDE;}
"("             {return LPAREN;}
")"             {return RPAREN;}
";"             {return SEMI;}
"{"             {return LBRACE;}
"}"             {return LBRACE;}
{number}        {return NUM;}
{identifier}    {return ID;}
{newline}       {lineno++;}
{whitespace}    {/* skip whitespace */}
"/*"             { 
                   char c;
                   int flag = 1;
                  do
                  { c = input();
                    if (c == EOF) break;
                    if (c == '\n') lineno++;
                    if (c == '*')
                    {
                      c = input();
                      if (c == '/') flag = 0;
                    }
                  } while (flag);
                }
.               {return ERROR;}

%%
TokenType getToken(void)
{ 
  static int firstTime = TRUE;
  TokenType currentToken;
  if (firstTime)
  { firstTime = FALSE;
    lineno++;
    yyin = source;
    yyout = listing;
  }
  currentToken = yylex();
  strncpy(tokenString,yytext,MAXTOKENLEN);
  if (TraceScan) {
    fprintf(listing,"\t%d: ",lineno);
    printToken(currentToken,tokenString);
  }
  return currentToken;
}

int yywrap()
{
  return 1;
}

4.2 实验演示

  • 使用flex cmm.l命令生成lex.yy.c

  • 将main.c lex.yy.c util.c globals.h util.h scan.h放入一个项目中，编译生成lexScanner.exe

  • 使用lexScanner .\fibonacci.cmm命令进行词法分析，结果如下：

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in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "fibonacci"
in Line:  1: get (
in Line:  1: get reserved word "int"
in Line:  1: get ID, name = "n"
in Line:  1: get )
in Line:  2: get {
in Line:  3: get reserved word "int"
in Line:  3: get ID, name = "cnt"
in Line:  3: get ;
in Line:  4: get reserved word "int"
in Line:  4: get ID, name = "firstFib"
in Line:  4: get ;
in Line:  5: get reserved word "int"
in Line:  5: get ID, name = "secondFib"
in Line:  5: get ;
in Line:  6: get reserved word "int"
in Line:  6: get ID, name = "fib"
in Line:  6: get ;
in Line:  8: get ID, name = "firstFib"
in Line:  8: get =
in Line:  8: get NUM, value = 1
in Line:  8: get ;
in Line:  9: get ID, name = "secondFib"
in Line:  9: get =
in Line:  9: get NUM, value = 1
in Line:  9: get ;
in Line: 10: get ID, name = "cnt"
in Line: 10: get =
in Line: 10: get NUM, value = 2
in Line: 10: get ;
in Line: 12: get reserved word "if"
in Line: 12: get (
in Line: 12: get ID, name = "n"
in Line: 12: get ==
in Line: 12: get NUM, value = 1
in Line: 12: get )
in Line: 13: get reserved word "return"
in Line: 13: get NUM, value = 1
in Line: 13: get ;
in Line: 14: get reserved word "else"
in Line: 14: get reserved word "if"
in Line: 14: get (
in Line: 14: get ID, name = "n"
in Line: 14: get ==
in Line: 14: get NUM, value = 2
in Line: 14: get )
in Line: 15: get reserved word "return"
in Line: 15: get NUM, value = 1
in Line: 15: get ;
in Line: 16: get reserved word "else"
in Line: 17: get {
in Line: 18: get reserved word "while"
in Line: 18: get (
in Line: 18: get ID, name = "cnt"
in Line: 18: get <
in Line: 18: get ID, name = "n"
in Line: 18: get )
in Line: 19: get {
in Line: 20: get ID, name = "fib"
in Line: 20: get =
in Line: 20: get ID, name = "firstFib"
in Line: 20: get +
in Line: 20: get ID, name = "secondFib"
in Line: 20: get ;
in Line: 21: get ID, name = "firstFib"
in Line: 21: get =
in Line: 21: get ID, name = "secondFib"
in Line: 21: get ;
in Line: 22: get ID, name = "secondFib"
in Line: 22: get =
in Line: 22: get ID, name = "fib"
in Line: 22: get ;
in Line: 23: get ID, name = "cnt"
in Line: 23: get =
in Line: 23: get ID, name = "cnt"
in Line: 23: get +
in Line: 23: get NUM, value = 1
in Line: 23: get ;
in Line: 24: get }
in Line: 25: get }
in Line: 26: get reserved word "return"
in Line: 26: get ID, name = "fib"
in Line: 26: get ;
in Line: 27: get }
in Line: 29: get reserved word "void"
in Line: 29: get ID, name = "main"
in Line: 29: get (
in Line: 29: get reserved word "void"
in Line: 29: get )
in Line: 30: get {
in Line: 31: get reserved word "int"
in Line: 31: get ID, name = "n"
in Line: 31: get ;
in Line: 32: get ID, name = "n"
in Line: 32: get =
in Line: 32: get ID, name = "input"
in Line: 32: get (
in Line: 32: get )
in Line: 32: get ;
in Line: 33: get ID, name = "output"
in Line: 33: get (
in Line: 33: get ID, name = "fibonacci"
in Line: 33: get (
in Line: 33: get ID, name = "n"
in Line: 33: get )
in Line: 33: get )
in Line: 33: get ;
in Line: 34: get }
in Line: 35: get EOF

5. BNF语法描述

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1 . program → declaration-list
  
2 . declaration-list → declaration-list declaration | declaration
  
3 . declaration → var-declaration | fun-declaration
  
4 . var-declaration → type-specifier ID;
  
5 . type-specifier → int | void
  
6 . fun-declaration → type-specifierID(params) | compound-stmt
  
7 . params → params-list | void
  
8 . param-list → param-list , param | param
  
9 . param → type-specifierID
 
10. compound-stmt → {local-declarationsstatement-list}
 
11. local-declarations → local-declarationsvar-declaration | empty
 
12. statement-list → statement-liststatement | empty
 
13. statement → expression-stmt 
                | compound-stmt 
                | selection-stmt
                | it eration-stmt 
                | return-stmt
 
14. expression-stmt → expression; | ;
 
15. selection-stmt → if(expression)statement
                   | if (expression)statement else statement
 
16. iteration-stmt → while(expression)statement
 
17. return-stmt → return; | return expression;
 
18. expression → var = expression | simple-expression
 
19. var → ID
 
20. simple-expression → additive-expression relop additive-expression 
                      | additive-expression
 
21. relop → <= | < | > | >= | == | !=
 
22. additive-expression → additive-expression addop term | term
 
23. addop → + | -
 
24. term → term mulop factor | factor
 
25. mulop → * | /
 
26. factor → (expression) | var | call | NUM
 
27. call → ID(args)
 
28. args → arg-list | empty
 
29. arg-list → arg-list, expression | expression

6. 语法分析程序

6.1 主要设计和实现思路

  • 定义结点类型：

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    typedef enum { StmtK, ExpK, DecK } NodeKind;
    /* statement kind, expression kind, declaration kind */
    typedef enum { IfK, WhileK, ReturnK, CallK, CompoundK } StmtKind;
    /* if kind, while kind, return kind, call kind, compound kind */
    typedef enum { OpK, IdK, ConstK, AssignK } ExpKind;
    /* oprator kind, identifier kind, const(num) kind, assign kind */
    typedef enum { ScalarDecK, FuncDecK } DecKind;
    /* scalar declaration kind, function declaration kind */
    typedef enum { Void, Integer, Function } ExpType;

  • 定义数据结构TreeNode：

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    typedef struct treeNode 
    {
        struct treeNode * child[MAXCHILDREN];
        struct treeNode * sibling;
        int lineno;
        NodeKind nodekind; 
        union 
        {
            StmtKind stmt;
            ExpKind  exp;
            DecKind  dec;
        } kind;

        TokenType op;
        int val;
        char *name;

        ExpType functionReturnType;
        ExpType variableDataType;
        ExpType expressionType;

        int isParameter;
        
        struct treeNode *declaration;
        
    } TreeNode;

  • 采用递归下降进行语法分析，参照C--语言的BNF语法，每个非终结符定义为一个函数，返回类型为TreeNode

  • 下降过程中，如果根据BNF范式，如果后一语句不为空，则将前一语句作为后一语句的树根，将他们全部连接起来，然后依次向下进行递归调用，根据相应的函数进行分析。

  • 分析结束后，调用util.c中的printTree()函数进行语法树的输出，函数如下：

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    #define INDENT   indentno += 4
    #define UNINDENT indentno -= 4


    static void printSpaces(void)
    {
        for (int i=0; i<indentno; ++i)
            fprintf(listing, " ");
    }

    char *typeName(ExpType type)
    {
        static char i[] = "integer";
        static char v[] = "void";
        static char invalid[] = "<<invalid type>>";

        switch (type)
        {
            case Integer: return i; break;
            case Void:    return v; break;
            default:      return invalid;
        }
    }

    void printTree(TreeNode *tree)
    {
        int i;

        INDENT;

        while (tree != NULL)
        {
            printSpaces();

            if (tree->nodekind == DecK)
            {
                switch(tree->kind.dec)
                {
                case ScalarDecK:
                    fprintf(listing,"[Scalar declaration \"%s\" of type \"%s\"]\n"
    			, tree->name, typeName(tree->variableDataType));
                    break;
                case ArrayDecK:
                    fprintf(listing, "[Array declaration \"%s\" of size %d"
                            " and type \"%s\"]\n",
                          tree->name, tree->val, typeName(tree->variableDataType));
                    break;
                case FuncDecK:
                    fprintf(listing, "[Function declaration \"%s()\""
                            " of return type \"%s\"]\n", 
                            tree->name, typeName(tree->functionReturnType));
                    break;
                default:
                    fprintf(listing, "<<<unknown declaration type>>>\n");
    		break;
                }
            }
            else if (tree->nodekind == ExpK)
            {
                switch(tree->kind.exp)
                {
                case OpK:
                    fprintf(listing, "[Operator \"");
                    printToken(tree->op, "");
                    fprintf(listing, "\"]\n");
                    break;
                case IdK:
                    fprintf(listing, "[Identifier \"%s", tree->name);
                    if (tree->val != 0) /* array indexing */
                        fprintf(listing, "[%d]", tree->val);
                    fprintf(listing, "\"]\n");
                    break;
                case ConstK:
                    fprintf(listing, "[Literal constant \"%d\"]\n", tree->val);
                    break;
                case AssignK:
                    fprintf(listing, "[Assignment]\n");
                    break;
                default:
                    fprintf(listing, "<<<unknown expression type>>>\n");
                    break;
                }
            }
            else if (tree->nodekind == StmtK)
            {
                switch(tree->kind.stmt)
                {
                case CompoundK:
                    fprintf(listing, "[Compound statement]\n");
                    break;
                        case IfK:
                            fprintf(listing, "[IF statement]\n");
                            break;
                        case WhileK:
                            fprintf(listing, "[WHILE statement]\n");
                            break;
                        case ReturnK:
                            fprintf(listing, "[RETURN statement]\n");
                            break;
                        case CallK:
                            fprintf(listing, "[Call to function \"%s()\"]\n",
                                     tree->name);
                            break;
                default:
                    fprintf(listing, "<<<unknown statement type>>>\n");
                    break;
                }
            }
            else
                fprintf(listing, "<<<unknown node kind>>>\n");

            for (i=0; i<MAXCHILDREN; ++i)
                printTree(tree->child[i]);

            tree = tree->sibling;
        }
     
        UNINDENT;
    }

6.2 递归下降语法分析程序代码

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#include "globals.h"
#include "util.h"
#include "scan.h"
#include "parse.h"

static TokenType token; // current token

static TreeNode *declaration_list(void);
static TreeNode *declaration(void);
static TreeNode *var_declaration(void);
static TreeNode *param(void);
static TreeNode *param_list(void);
static TreeNode *compound_statement(void);
static TreeNode *local_declarations(void);
static TreeNode *statement_list(void);
static TreeNode *statement(void);
static TreeNode *expression_statement(void);
static TreeNode *if_statement(void);
static TreeNode *while_statement(void);
static TreeNode *return_statement(void);
static TreeNode *expression(void);
static TreeNode *simple_expression(TreeNode *passdown);
static TreeNode *additive_expression(TreeNode *passdown);
static TreeNode *term(TreeNode *passdown);
static TreeNode *factor(TreeNode *passdown);
static TreeNode *args(void);
static TreeNode *arg_list(void);
static TreeNode *identifier_statement(void);

static void syntaxError(char *message)
{
    fprintf(listing, ">>> Syntax error at line %d: %s", lineno, message);
}

static void match(TokenType expected)
{
    if (token == expected)
        token = getToken();
    else
    {
        syntaxError("unexpected token ");
        printToken(token, tokenString);
        fprintf(listing, "\n");
    }
}

static ExpType matchType()
{
    ExpType t_type = Void;

    switch (token)
    {
        case INT:
            t_type = Integer;
            token = getToken();
            break;
        case VOID:
            t_type = Void;
            token = getToken();
            break;
        default:
        {
            syntaxError("expected a type identifier but got a ");
            printToken(token, tokenString);
            fprintf(listing, "\n");
            break;
        }
    }

    return t_type;
}

static int isAType(TokenType tok)
{
    if ((tok == INT) || (tok == VOID))
        return TRUE;
    else
        return FALSE;
}

static TreeNode * declaration_list(void)
{
    TreeNode * tree;
    TreeNode * ptr;

    tree = declaration();
    ptr = tree;

    while (token != ENDOFFILE)
    {
        TreeNode *tmp; 

        tmp = declaration();
        if ((tmp != NULL) && (ptr != NULL))
        {
            ptr->sibling = tmp;
            ptr = tmp;
        }
    }

    return tree;
}

static TreeNode *declaration(void)
{
    TreeNode *tree = NULL;
    ExpType declaration_type;
    char *identifier;

    declaration_type = matchType(); 
    identifier = copyString(tokenString);
    match(ID);

    switch (token)
    {
        case SEMI: /* variable declaration */
            tree = newDecNode(ScalarDecK);
            if (tree != NULL)
            {
                tree->variableDataType = declaration_type;
                tree->name = identifier;
            }
            match(SEMI);
            break;

        case LPAREN: /* function declaration */
            tree = newDecNode(FuncDecK);
            if (tree != NULL)
            {
                tree->functionReturnType = declaration_type;
                tree->name = identifier;
            }
            match(LPAREN);
            if (tree != NULL)
                tree->child[0] = param_list();
            match(RPAREN);
            if (tree != NULL)
                tree->child[1] = compound_statement();
            break;

        default:
            syntaxError("unexpected token ");
            printToken(token, tokenString);
            fprintf(listing, "\n");
            token = getToken();
            break;
    }

    return tree;
}

static TreeNode *var_declaration(void)
{
    TreeNode *tree = NULL;
    ExpType declaration_type;
    char *identifier;

    declaration_type = matchType();
    identifier = copyString(tokenString);
    match(ID);

    if(token == SEMI)
    {   
        tree = newDecNode(ScalarDecK); /* variable declaration */ 
        if (tree != NULL)
        {
            tree->variableDataType = declaration_type;
            tree->name = identifier;
        }
        match(SEMI);
    }
    else
    {
        syntaxError("unexpected token ");
        printToken(token, tokenString);
        fprintf(listing, "\n");
        token = getToken();
    }
    return tree;
}

static TreeNode *param(void)
{
    TreeNode *tree;
    ExpType parmType;
    char *identifier;

    parmType = matchType(); /* get type of formal parameter */
    identifier = copyString(tokenString);
    match(ID);

    tree = newDecNode(ScalarDecK);

    if (tree != NULL)
    {
        tree->name = identifier;
        tree->val = 0;
        tree->variableDataType = parmType;
        tree->isParameter = TRUE;
    }

    return tree;
}

static TreeNode *param_list(void)
{
    TreeNode *tree;
    TreeNode *ptr;
    TreeNode *newNode;

    if (token == VOID) /* void param */
    {
        match(VOID);
        return NULL;
    }

    tree = param();
    ptr = tree;

    while ((tree != NULL) && (token == COMMA)) /* mutiple params */
    {
        match(COMMA);
        newNode = param();
        if (newNode != NULL)
        {
            ptr->sibling = newNode;
            ptr = newNode;
        }
    }

    return tree;
}

static TreeNode *compound_statement(void)
{
    TreeNode *tree = NULL;

    match(LBRACE);

    if ((token != RBRACE) && (tree = newStmtNode(CompoundK)))
    {
        if (isAType(token))
            tree->child[0] = local_declarations();
        if (token != RBRACE)
            tree->child[1] = statement_list();
    }
    match(RBRACE);

    return tree;
}

static TreeNode *local_declarations(void)
{
    TreeNode *tree;
    TreeNode *ptr;
    TreeNode *newNode;

    /* find first variable declaration, if it exists */
    if (isAType(token))
        tree = var_declaration();

    /* subsetmpuent variable declarations */
    if (tree != NULL)
    {
        ptr = tree;

        while (isAType(token))
        {
            newNode = var_declaration();
            if (newNode != NULL)
            {
                ptr->sibling = newNode;
                ptr = newNode;
            }
        }
    }

    return tree;
}

static TreeNode *statement_list(void)
{
    TreeNode *tree = NULL;
    TreeNode *ptr;
    TreeNode *newNode;

    if (token != RBRACE)
    {
        tree = statement();
        ptr = tree;

        while (token != RBRACE)
        {
            newNode = statement();
            if ((ptr != NULL) && (newNode != NULL))
            {
                ptr->sibling = newNode;
                ptr = newNode;
            }
        }
    }

    return tree;
}

static TreeNode *statement(void)
{
    TreeNode *tree = NULL;

    switch (token)
    {
        case IF:
            tree = if_statement();
            break;
        case WHILE:
            tree = while_statement();
            break;
        case RETURN:
            tree = return_statement();
            break;
        case LBRACE:
            tree = compound_statement();
            break;
        case ID:
        case SEMI:
        case LPAREN:
        case NUM:
            tree = expression_statement();
            break;
        default:
            syntaxError("unexpected token ");
            printToken(token, tokenString);
            fprintf(listing, "\n");
            token = getToken();
            break;
    }

    return tree;
}

static TreeNode *expression_statement(void)
{
    TreeNode *tree = NULL;

    if (token == SEMI)
        match(SEMI);
    else if (token != RBRACE)
    {
        tree = expression();
        match(SEMI);
    }

    return tree;
}

static TreeNode *if_statement(void)
{
    TreeNode *tree;
    TreeNode *expr;
    TreeNode *ifStmt;
    TreeNode *elseStmt = NULL;


    match(IF);
    match(LPAREN);
    expr = expression();
    match(RPAREN);
    ifStmt = statement();

    if (token == ELSE)
    {
        match(ELSE);
        elseStmt = statement();
    }

    tree = newStmtNode(IfK);
    if (tree != NULL)
    {
        tree->child[0] = expr;
        tree->child[1] = ifStmt;
        tree->child[2] = elseStmt;
    }

    return tree;
}

static TreeNode *while_statement(void)
{
    TreeNode *tree;
    TreeNode *expr;
    TreeNode *stmt;

    match(WHILE);
    match(LPAREN);
    expr = expression();
    match(RPAREN);
    stmt = statement();

    tree = newStmtNode(WhileK);
    if (tree != NULL)
    {
        tree->child[0] = expr;
        tree->child[1] = stmt;
    }

    return tree;
}

static TreeNode *return_statement(void)
{
    TreeNode *tree;
    TreeNode *expr = NULL;

    match(RETURN);

    tree = newStmtNode(ReturnK);
    if (token != SEMI)
        expr = expression();

    if (tree != NULL)
        tree->child[0] = expr;

    match(SEMI);

    return tree;
}

static TreeNode *expression(void)
{
    TreeNode *tree = NULL;
    TreeNode *lvalue = NULL;
    TreeNode *rvalue = NULL;
    int gotLvalue = FALSE; 


    if (token == ID)
    {
        lvalue = identifier_statement();
        gotLvalue = TRUE;
    }

    /* assign */
    if ((gotLvalue == TRUE) && (token == ASSIGN))
    {
        if ((lvalue != NULL) && (lvalue->nodekind == ExpK) &&
            (lvalue->kind.exp == IdK))
        {
            match(ASSIGN);
            rvalue = expression();
            tree = newExpNode(AssignK);
            if (tree != NULL)
            {
                tree->child[0] = lvalue; /* left  value */
                tree->child[1] = rvalue; /* right value*/
            }
        }
        else
        {
            syntaxError("attempt to assign to something not an lvalue\n");
            token = getToken();
        }
    }
    else
        tree = simple_expression(lvalue);

    return tree;
}

static TreeNode *simple_expression(TreeNode *passdown)
{
    TreeNode *tree;
    TreeNode *lExpr = NULL;
    TreeNode *rExpr = NULL;
    TokenType operator;

    lExpr = additive_expression(passdown);

    if ((token == LTE) || (token == GTE) || (token == GT) || 
        (token == LT) || (token == EQ) || (token == NE))
    {
        operator = token;
        match(token);
        rExpr = additive_expression(NULL);

        tree = newExpNode(OpK);
        if (tree != NULL)
        {
            tree->child[0] = lExpr;
            tree->child[1] = rExpr;
            tree->op = operator;
        }
    }
    else
        tree = lExpr;

    return tree;
}

static TreeNode *additive_expression(TreeNode *passdown)
{
    TreeNode *tree;
    TreeNode *newNode;

    tree = term(passdown);

    while ((token == PLUS) || (token == MINUS))
    {
        newNode = newExpNode(OpK);
        if (newNode != NULL)
        {
            newNode->child[0] = tree;
            newNode->op = token;
            tree = newNode;
            match(token);
            tree->child[1] = term(NULL);
        }
    }

    return tree;
}

static TreeNode *term(TreeNode *passdown)
{
    TreeNode *tree;
    TreeNode *newNode;

    tree = factor(passdown);

    while ((token == TIMES) || (token == DIVIDE))
    {
        newNode = newExpNode(OpK);

        if (newNode != NULL)
        {
            newNode->child[0] = tree;
            newNode->op = token;
            tree = newNode;
            match(token);
            newNode->child[1] = factor(NULL);
        }
    }

    return tree;
}

static TreeNode *factor(TreeNode *passdown)
{
    TreeNode *tree = NULL;

    /* If the subtree in "passdown" is a Factor, pass it back. */
    if (passdown != NULL) return passdown;

    if (token == ID)
    {
        tree = identifier_statement();
    }
    else if (token == LPAREN)
    {
        match(LPAREN);
        tree = expression();
        match(RPAREN);
    }
    else if (token == NUM)
    {
        tree = newExpNode(ConstK);
        if (tree != NULL)
        {
            tree->val = atoi(tokenString);
            tree->variableDataType = Integer;
        }
        match(NUM);
    }
    else
    {
        syntaxError("unexpected token ");
        printToken(token, tokenString);
        fprintf(listing, "\n");
        token = getToken();
    }

    return tree;
}

static TreeNode *identifier_statement(void)
{
    TreeNode *tree;
    TreeNode *expr = NULL;
    TreeNode *arguments = NULL;
    char *identifier;

    if (token == ID)
        identifier = copyString(tokenString);
    match(ID);

    if (token == LPAREN)
    {
        match(LPAREN);
        arguments = args();
        match(RPAREN);

        tree = newStmtNode(CallK);
        if (tree != NULL)
        {
            tree->child[0] = arguments;
            tree->name = identifier;
        }
    }
    else
    {
        tree = newExpNode(IdK);
        if (tree != NULL)
        {
            tree->child[0] = expr;
            tree->name = identifier;
        }
    }

    return tree;
}

static TreeNode *args(void)
{
    TreeNode *tree = NULL;

    if (token != RPAREN)
        tree = arg_list();

    return tree;
}

static TreeNode *arg_list(void)
{
    TreeNode *tree;
    TreeNode *ptr;
    TreeNode *newNode;

    tree = expression();
    ptr = tree;

    while (token == COMMA)
    {
        match(COMMA);
        newNode = expression();

        if ((ptr != NULL) && (tree != NULL))
        {
            ptr->sibling = newNode;
            ptr = newNode;
        }
    }

    return tree;
}

TreeNode *Parse(void)
{
    TreeNode *t;

    token = getToken();
    t = declaration_list();
    if (token != ENDOFFILE)
        syntaxError("Unexpected symbol at end of file\n");

    /* t points to the fully-constructed syntax tree */
    return t;
}

6.3 实验演示

  • 求三个整数中的最大值

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    [Function declaration "max()" of return type "integer"]
        [Scalar declaration "x" of type "integer"]
        [Scalar declaration "y" of type "integer"]
        [Scalar declaration "z" of type "integer"]
        [Compound statement]
            [Scalar declaration "biggest" of type "integer"]
            [Assignment]
                [Identifier "biggest"]
                [Identifier "x"]
            [IF statement]
                [Operator ">"]
                    [Identifier "y"]
                    [Identifier "biggest"]
                [Assignment]
                    [Identifier "biggest"]
                    [Identifier "y"]
            [IF statement]
                [Operator ">"]
                    [Identifier "z]"]
                    [Identifier "biggest"]
                [Assignment]
                    [Identifier "biggest"]
                    [Identifier "z"]
            [RETURN statement]
                [Identifier "biggest"]
    [Function declaration "main()" of return type "void"]
        [Compound statement]
            [Scalar declaration "x" of type "integer"]
            [Scalar declaration "y" of type "integer"]
            [Scalar declaration "z" of type "integer"]
            [Scalar declaration "biggest" of type "integer"]
            [Assignment]
                [Identifier "x"]
                [Call to function "input()"]
            [Assignment]
                [Identifier "y"]
                [Call to function "input()"]
            [Assignment]
                [Identifier "z"]
                [Call to function "input()"]
            [Assignment]
                [Identifier "biggest"]
                [Call to function "max()"]
                    [Identifier "x"]
                    [Identifier "y"]
                    [Identifier "z"]
            [Call to function "output()"]
                [Identifier "biggest"]

  • 给定 N，求 1 到 N 之和

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    [Function declaration "sum()" of return type "integer"]
        [Scalar declaration "n" of type "integer"]
        [Compound statement]
            [Scalar declaration "result" of type "integer"]
            [Scalar declaration "i" of type "integer"]
            [Assignment]
                [Identifier "i"]
                [Literal constant "1"]
            [Assignment]
                [Identifier "result"]
                [Literal constant "0"]
            [WHILE statement]
                [Operator "<="]
                    [Identifier "i"]
                    [Identifier "n"]
                [Compound statement]
                    [Assignment]
                        [Identifier "result"]
                        [Operator "+"]
                            [Identifier "result"]
                            [Identifier "i"]
                    [Assignment]
                        [Identifier "i"]
                        [Operator "+"]
                            [Identifier "i"]
                            [Literal constant "1"]
            [RETURN statement]
                [Identifier "result"]
    [Function declaration "main()" of return type "void"]
        [Compound statement]
            [Scalar declaration "n" of type "integer"]
            [Scalar declaration "s" of type "integer"]
            [Assignment]
                [Identifier "n"]
                [Call to function "intput()"]
            [Assignment]
                [Identifier "s"]
                [Call to function "sum()"]
                    [Identifier "n"]
            [Call to function "output()"]
                [Identifier "s"]

  • 计算第n个斐波那契数

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    [Function declaration "fibonacci()" of return type "integer"]
        [Scalar declaration "n" of type "integer"]
        [Compound statement]
            [Scalar declaration "cnt" of type "integer"]
            [Scalar declaration "firstFib" of type "integer"]
            [Scalar declaration "secondFib" of type "integer"]
            [Scalar declaration "fib" of type "integer"]
            [Assignment]
                [Identifier "firstFib"]
                [Literal constant "1"]
            [Assignment]
                [Identifier "secondFib"]
                [Literal constant "1"]
            [Assignment]
                [Identifier "cnt"]
                [Literal constant "2"]
            [IF statement]
                [Operator "=="]
                    [Identifier "n"]
                    [Literal constant "1"]
                [RETURN statement]
                    [Literal constant "1"]
                [IF statement]
                    [Operator "=="]
                        [Identifier "n"]
                        [Literal constant "2"]
                    [RETURN statement]
                        [Literal constant "1"]
                    [Compound statement]
                        [WHILE statement]
                            [Operator "<"]
                                [Identifier "cnt"]
                                [Identifier "n"]
                            [Compound statement]
                                [Assignment]
                                    [Identifier "fib"]
                                    [Operator "+"]
                                        [Identifier "firstFib"]
                                        [Identifier "secondFib"]
                                [Assignment]
                                    [Identifier "firstFib"]
                                    [Identifier "secondFib"]
                                [Assignment]
                                    [Identifier "secondFib"]
                                    [Identifier "fib"]
                                [Assignment]
                                    [Identifier "cnt"]
                                    [Operator "+"]
                                        [Identifier "cnt"]
                                        [Literal constant "1"]
            [RETURN statement]
                [Identifier "fib"]
    [Function declaration "main()" of return type "void"]
        [Compound statement]
            [Scalar declaration "n" of type "integer"]
            [Assignment]
                [Identifier "n"]
                [Call to function "input()"]
            [Call to function "output()"]
                [Call to function "fibonacci()"]
                    [Identifier "n"]

7. 语义分析程序

7.1 主要设计和实现思路

7.1.1 符号表构造

首先通过void buildSymbolTable(TreeNode *syntaxTree)函数进行符号表构造

  • static void drawRuler(FILE *output, char *string)函数，用于确定符号表的格式,打印分割线
  • static void declarePredefines(void)函数，用来将C--语言内置的input()和output()函数添加进符号表
  • static void startBuildSymbolTable(TreeNode *syntaxTree)函数开始构造符号表：
    • 该函数的参数为语法树根结点，通过遍历整个语法树，来寻找结点类型为DECK（声明结点）的结点，并将他们插入到符号表中，插入的过程中将进行检测。
    • 声明也分为两种：变量的声明与函数的声明：变量的声明可直接插入到符号表；而函数的声明中可能有变量声明，此时，将会调用之前提到过的drawruler()函数，增加一张符号表，用于处理该函数内部的变量声明。
    • 对于非声明类结点，只需进行错误检测，即在既有的符号表中查询其是否进行过声明。

7.1.2 类型检查

首先通过traverse(syntaxTree, nullProc, checkNode)函数，检查相邻语法树结点的词法属性来判断是否出错。

  • static void nullProc(TreeNode *syntaxTree)函数直接返回（即遇到叶子结点），不进行其他操作
  • static void checkNode(TreeNode *syntaxTree)函数通过遍历语法树，遍历到当前的一个结点之后，检查该结点的相邻结点是否符合语法规则，如果不符合就报错，如果符合就可以继续遍历。

7.2 类型检查语义分析程序代码

7.2.1 symtab.c

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#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <stdio.h>
#include <stdlib.h>

#include "Globals.h"
#include "SymTab.h"
#include "Util.h"

#define MAXTABLESIZE 233
#define HIGHWATERMARK "__invalid__"

/* The hash table itself */
static HashNodePtr hashtable[MAXTABLESIZE];

/* The "temporary list", used to track scopes. */
static HashNodePtr tempList;

extern int TraceAnalyse;
int scopeDepth;

static HashNodePtr allocateSymbolNode(char *name,
                                      TreeNode *declaration,
                                      int lineDefined);

/* hashfunction(): takes a string and generates a hash value. */
static int hashFunction(char *key);

/* error reporting */
static void flagError(char *message);

/* used in symbol table scope dump */
static char *formatSymbolType(TreeNode *node);

/* the guts of dumpCurrentScope() */
static void startDumpCurrentScope(HashNodePtr cursor);

void initSymbolTable(void)
{
    memset(hashtable, 0, sizeof(HashNodePtr) * MAXTABLESIZE);
    tempList = NULL;
}

void insertSymbol(char *name, TreeNode *symbolDefNode, int lineDefined)
{
    char errorString[80]; 

    HashNodePtr newHashNode, temp;
    int hashBucket;

    /* If the symbol already exists, flag an error */
    if (symbolAlreadyDeclared(name))
    {
        sprintf(errorString, "duplicate identifier \"%s\"\n", name);
        flagError(errorString);
    }
    else
    {
        /* Locate bucket we're using */
        hashBucket = hashFunction(name);
        /* Allocate and insert record on front of bucket */
        newHashNode = allocateSymbolNode(name, symbolDefNode, lineDefined);
        if (newHashNode != NULL)
        {
            temp = hashtable[hashBucket];
            hashtable[hashBucket] = newHashNode;
            newHashNode->next = temp;
        }

        /* Stick node on front of "tempList" */
        newHashNode = allocateSymbolNode(name, symbolDefNode, lineDefined);
        if (newHashNode != NULL)
        {
            temp = tempList;
            tempList = newHashNode;
            tempList->next = temp;
        }
    }
}

/* Check to see if the symbol given by "name" is already declared in thecurrent scope. */

int symbolAlreadyDeclared(char *name)
{
    int symbolFound = FALSE;
    HashNodePtr cursor;

    /* Scan "tempList" within _current_ scope for duplicate definition */
    cursor = tempList;

    while ((cursor != NULL) && (!symbolFound) && ((strcmp(cursor->name, HIGHWATERMARK) != 0)))
    {
        if (strcmp(name, cursor->name) == 0)
            symbolFound = TRUE;
        else
            cursor = cursor->next;
    }

    return (symbolFound);
}

HashNodePtr lookupSymbol(char *name)
{
    HashNodePtr cursor;
    int hashBucket;    /* hash bucket on which to conduct our search */
    int found = FALSE; 

    hashBucket = hashFunction(name);
    cursor = hashtable[hashBucket];

    while (cursor != NULL)
    {
        if (strcmp(name, cursor->name) == 0)
        {
            found = TRUE;
            break;
        }

        cursor = cursor->next;
    }

    if (found == TRUE)
        return cursor;
    else
        return NULL;
}

/*
 * Use recursion to dump symbols out in "reverse-reverse" order.. i.e the
 *  right way around...
 */

void dumpCurrentScope()
{
    HashNodePtr cursor;

    cursor = tempList;

    /* if the current scope isn't empty,  dump it out */
    if ((cursor != NULL) && (strcmp(HIGHWATERMARK, cursor->name)))
        startDumpCurrentScope(cursor);
}

#define IDENT_LEN 12

static void startDumpCurrentScope(HashNodePtr cursor)
{
    char paddedIdentifier[IDENT_LEN + 1];
    char *typeInformation; /* used to catch result of formatSymbolType */

    if ((cursor->next != NULL) && (strcmp(cursor->next->name, HIGHWATERMARK) != 0))
        startDumpCurrentScope(cursor->next);

    /* pad identifier name */
    memset(paddedIdentifier, ' ', IDENT_LEN);
    memmove(paddedIdentifier, cursor->name, strlen(cursor->name));
    paddedIdentifier[IDENT_LEN] = '\0';

    /* output symbol table entry */
    typeInformation = formatSymbolType(cursor->declaration);

    fprintf(listing, "%3d   %s   %7d     %c    %s\n",
            scopeDepth,
            paddedIdentifier,
            cursor->lineFirstReferenced,
            cursor->declaration->isParameter ? 'Y' : 'N',
            typeInformation);

    /* Prevent a memory leak */
    free(typeInformation);
}

void newScope()
{
    HashNodePtr newNode, temp;

    /*
     * This function is short and sweet: we just append a "high water mark"
     *  on "tempList".
     */

    newNode = allocateSymbolNode(HIGHWATERMARK, NULL, 0);
    if (newNode != NULL)
    {
        temp = tempList;
        tempList = newNode;
        tempList->next = temp;
    }
}

void endScope()
{
    /*
     *  endScope()'s job is to delete all symbols in the current scope.  It
     *  works by scanning "tempList" from the front and for each record
     *  before the high-water mark, it deletes each symbol's occurrence in
     *  the hash table.  This is done until the high-water mark is consumed.
     */

    HashNodePtr hashPtr;
    HashNodePtr temp; /* used in freeing HashNodes */
    int hashBucket;

    while ((tempList != NULL) && (strcmp(HIGHWATERMARK, tempList->name)) != 0)
    {
        /* locate this node in the hash table, delete it */
        hashBucket = hashFunction(tempList->name);
        hashPtr = hashtable[hashBucket];

        /*
         *  INVARIANT: since symbols were inserted into the hash table _and_
         *    tempList in the same order, the name of the symbol on the
         *    front of the hash bucket _must_ be the same as the one under
         *    tempListPtr.
         */

        assert((tempList != NULL) && (hashtable[hashBucket] != NULL));
        assert(strcmp(tempList->name, hashPtr->name) == 0);

        /* delete from hash table */
        temp = hashtable[hashBucket]->next;
        free(hashtable[hashBucket]);
        hashtable[hashBucket] = temp;

        /* ... and from second list */
        temp = tempList->next;
        free(tempList);
        tempList = temp;
    }

    /* delete high water mark */
    assert(strcmp(tempList->name, HIGHWATERMARK) == 0);
    temp = tempList->next;
    free(tempList);
    tempList = temp;
}

static HashNodePtr allocateSymbolNode(char *name,
                                      TreeNode *declaration,
                                      int lineDefined)
{
    HashNode *temp;

    temp = (HashNode *)malloc(sizeof(HashNode));
    if (temp == NULL)
    {
        Error = TRUE;
        fprintf(listing,
                "*** Out of memory allocating memory for symbol table\n");
    }
    else
    {
        temp->name = copyString(name);
        temp->declaration = declaration;
        temp->lineFirstReferenced = lineDefined;
        temp->next = NULL;
    }

    return temp;
}

/* Power-of-two multiplier in hash function */
#define SHIFT 4

/* Code borrowed from Louden p.522 */
static int hashFunction(char *key)
{
    int temp = 0;
    int i = 0;

    while (key[i] != '\0')
    {
        temp = ((temp << SHIFT) + key[i]) % MAXTABLESIZE;
        ++i;
    }

    return temp;
}

static void flagError(char *message)
{
    fprintf(listing, ">>> Semantic error (symbol table): %s", message);
    Error = TRUE; /* global variable to inhibit subseq. passes on error */
}

static char *formatSymbolType(TreeNode *node)
{
    char stringBuffer[100];

    if ((node == NULL) || (node->nodekind != DecK))
        strcpy(stringBuffer, "<<ERROR>>");
    else
    {
        /* node is a declaration */
        switch (node->kind.dec)
        {
        case ScalarDecK:
            sprintf(stringBuffer, "Scalar of type %s",
                    typeName(node->variableDataType));
            break;
        case ArrayDecK:
            sprintf(stringBuffer, "Array of type %s with %d elements",
                    typeName(node->variableDataType), node->val);
            break;
        case FuncDecK:
            sprintf(stringBuffer, "Function with return type %s",
                    typeName(node->functionReturnType));
            break;
        default:
            strcpy(stringBuffer, "<<UNKNOWN>>");
            break;
        }
    }

    return copyString(stringBuffer);
}

7.2.2 analyse.c

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#include "Analyse.h"
#include "Globals.h"
#include "SymTab.h"
#include "Util.h"

/* draw a ruler on the screen */
static void drawRuler(FILE *output, char *string);

/* the guts of buildSymbolTable() */
static void startBuildSymbolTable(TreeNode *syntaxTree);

/* flag an error from the type checker */
static void flagSemanticError(char *str);

/* generic tree traversal routine */
static void traverse(TreeNode *syntaxTree,
                     void (*preProc)(TreeNode *),
                     void (*postProc)(TreeNode *));

/* routine to perform the actual type check on a node */
static void checkNode(TreeNode *syntaxTree);

/* dummy do-nothing procedure used to keep traversal() happy */
static void nullProc(TreeNode *syntaxTree);

/* traverse the syntax tree, marking global variables as such */
void markGlobals(TreeNode *tree);

/* declare the C-minus "built-in" input() and output() routines */
static void declarePredefines(void);

/* type-check functions' formal parameters against actual parameters */
static int checkFormalAgainstActualParms(TreeNode *formal, TreeNode *actual);

void buildSymbolTable(TreeNode *syntaxTree)
{
    /* Format headings */
    if (TraceAnalyse)
    {
        drawRuler(listing, "");
        fprintf(listing,
                "Scope Identifier        Line   Is a   Symbol type\n");
        fprintf(listing,
                "depth                   Decl.  parm?\n");
    }

    declarePredefines(); /* make input() and output() visible in globals */
    startBuildSymbolTable(syntaxTree);
}

void typeCheck(TreeNode *syntaxTree)
{
    traverse(syntaxTree, nullProc, checkNode);
}

/* make input() and output() visible in globals */
static void declarePredefines(void)
{
    TreeNode *input;
    TreeNode *output;
    TreeNode *temp;

    /* define "int input(void)" */
    input = newDecNode(FuncDecK);
    input->name = copyString("input");
    input->functionReturnType = Integer;
    input->expressionType = Function;

    /* define "void output(int)" */
    temp = newDecNode(ScalarDecK);
    temp->name = copyString("arg");
    temp->variableDataType = Integer;
    temp->expressionType = Integer;

    output = newDecNode(FuncDecK);
    output->name = copyString("output");
    output->functionReturnType = Void;
    output->expressionType = Function;
    output->child[0] = temp;

    /* get input() and output() added to global scope */
    insertSymbol("input", input, 0);
    insertSymbol("output", output, 0);
}

static void startBuildSymbolTable(TreeNode *syntaxTree)
{
    int i;                     /* iterate over node children */
    HashNodePtr currentSymbol; /* symbol being looked up */
    char errorMessage[80];

    /* used to decorate RETURN nodes with enclosing procedure */
    static TreeNode *enclosingFunction = NULL;

    while (syntaxTree != NULL)
    {
        /* Examine current symbol: if it's a declaration, insert intosymbol table. */
        if (syntaxTree->nodekind == DecK)
            insertSymbol(syntaxTree->name, syntaxTree, syntaxTree->lineno);

        /* If entering a new function, tell the symbol table */
        if ((syntaxTree->nodekind == DecK) && (syntaxTree->kind.dec == FuncDecK))
        {
            /* record the enclosing procedure declaration */
            enclosingFunction = syntaxTree;

            if (TraceAnalyse)
                drawRuler(listing, syntaxTree->name);

            newScope();
            ++scopeDepth;
        }

        /* if entering a compound-statement, create a new scope as well */
        if ((syntaxTree->nodekind == StmtK) && (syntaxTree->kind.stmt == CompoundK))
        {
            newScope();
            ++scopeDepth;
        }

        /* if it's an identifier, it needs to be check symbol table*/
        if (((syntaxTree->nodekind == ExpK) && (syntaxTree->kind.exp == IdK)) 
         || ((syntaxTree->nodekind == StmtK) && (syntaxTree->kind.stmt == CallK)))
        {
            currentSymbol = lookupSymbol(syntaxTree->name);
            if (currentSymbol == NULL)
            {
                /* operation failed; say so to user */
                sprintf(errorMessage,
                        "identifier \"%s\" unknown or out of scope\n",
                        syntaxTree->name);
                flagSemanticError(errorMessage);
            }
            else
                syntaxTree->declaration = currentSymbol->declaration;
        }

        /* mark return type */
        if ((syntaxTree->nodekind == StmtK) &&
            (syntaxTree->kind.stmt == ReturnK))
        {
            syntaxTree->declaration = enclosingFunction;
        }

        for (i = 0; i < MAXCHILDREN; ++i)
            startBuildSymbolTable(syntaxTree->child[i]);

        /* If leaving a scope, tell the symbol table */
        if (((syntaxTree->nodekind == DecK) && (syntaxTree->kind.dec == FuncDecK)) 
         || ((syntaxTree->nodekind == StmtK) && (syntaxTree->kind.stmt == CompoundK)))
        {
            if (TraceAnalyse)
                dumpCurrentScope();
            --scopeDepth;
            endScope();
        }
        syntaxTree = syntaxTree->sibling;
    }
}

static void drawRuler(FILE *output, char *string)
{
    int length;
    int numTrailingDashes;
    int i;

    /* empty string */
    if (strcmp(string, "") == 0)
        length = 0;
    else
        length = strlen(string) + 2;

    fprintf(output, "---");
    if (length > 0)
        fprintf(output, " %s ", string);
    numTrailingDashes = 45 - length;

    for (i = 0; i < numTrailingDashes; ++i)
        fprintf(output, "-");
    fprintf(output, "\n");
}

static void flagSemanticError(char *str)
{
    fprintf(listing, ">>> Semantic error (type checker): %s", str);
    Error = TRUE;
}

/* generic tree traversal routine */
static void traverse(TreeNode *syntaxTree,
                     void (*preProc)(TreeNode *),
                     void (*postProc)(TreeNode *))
{
    while (syntaxTree != NULL)
    {
        preProc(syntaxTree);
        for (int i = 0; i < MAXCHILDREN; ++i)
            traverse(syntaxTree->child[i], preProc, postProc);
        postProc(syntaxTree);
        syntaxTree = syntaxTree->sibling;
    }
}

static int checkFormalAgainstActualParms(TreeNode *formal, TreeNode *actual)
{
    TreeNode *firstList;
    TreeNode *secondList;

    firstList = formal->child[0];
    secondList = actual->child[0];

    while ((firstList != NULL) && (secondList != NULL))
    {
        if (firstList->expressionType != secondList->expressionType)
            return FALSE;

        if (firstList)
            firstList = firstList->sibling;
        if (secondList)
            secondList = secondList->sibling;
    }

    if (((firstList == NULL) && (secondList != NULL)) 
     || ((firstList != NULL) && (secondList == NULL)))
        return FALSE;

    return TRUE;
}

static void checkNode(TreeNode *syntaxTree)
{
    char errorMessage[100];

    switch (syntaxTree->nodekind)
    {
    case DecK:

        switch (syntaxTree->kind.dec)
        {
        case ScalarDecK:
            syntaxTree->expressionType = syntaxTree->variableDataType;
            break;

        case ArrayDecK:
            syntaxTree->expressionType = Array;
            break;

        case FuncDecK:
            syntaxTree->expressionType = Function;
            break;
        }

        break; /* case DecK */

    case StmtK:

        switch (syntaxTree->kind.stmt)
        {
        case IfK:

            if (syntaxTree->child[0]->expressionType != Integer)
            {
                sprintf(errorMessage,
                        "IF-expression must be integer (line %d)\n",
                        syntaxTree->lineno);
                flagSemanticError(errorMessage);
            }
            break;

        case WhileK:

            if (syntaxTree->child[0]->expressionType != Integer)
            {
                sprintf(errorMessage,
                        "WHILE-expression must be integer (line %d)\n",
                        syntaxTree->lineno);
                flagSemanticError(errorMessage);
            }
            break;

        case CallK:

            /*  Check types and numbers of formal against actual parameters */
            if (!checkFormalAgainstActualParms(syntaxTree->declaration,
                                               syntaxTree))
            {
                sprintf(errorMessage, "formal and actual parameters to "
                                      "function don\'t match (line %d)\n",
                        syntaxTree->lineno);
                flagSemanticError(errorMessage);
            }
            syntaxTree->expressionType = syntaxTree->declaration->functionReturnType;
            break;

        case ReturnK:

            /* match return type */
            if (syntaxTree->declaration->functionReturnType == Integer)
            {
                if ((syntaxTree->child[0] == NULL) || 
                    (syntaxTree->child[0]->expressionType != Integer))
                {
                    sprintf(errorMessage, "RETURN-expression is either "
                                          "missing or not integer (line %d)\n",
                            syntaxTree->lineno);
                    flagSemanticError(errorMessage);
                }
            }
            else if (syntaxTree->declaration->functionReturnType == Void)
            {
                /* does a return-expression exist? complain */
                if (syntaxTree->child[0] != NULL)
                {
                    sprintf(errorMessage, "RETURN-expression must be"
                                          "void (line %d)\n",
                            syntaxTree->lineno);
                }
            }

            break;

        case CompoundK:

            syntaxTree->expressionType = Void;
            break;
        }

        break; /* case StmtK */

    case ExpK:

        switch (syntaxTree->kind.exp)
        {
        case OpK:
            /* Arithmetic operators */
            if ((syntaxTree->op == PLUS) || (syntaxTree->op == MINUS) ||
                (syntaxTree->op == TIMES) || (syntaxTree->op == DIVIDE))
            {
                if ((syntaxTree->child[0]->expressionType == Integer) &&
                    (syntaxTree->child[1]->expressionType == Integer))
                    syntaxTree->expressionType = Integer;
                else
                {
                    sprintf(errorMessage, "arithmetic operators must have "
                                          "integer operands (line %d)\n",
                            syntaxTree->lineno);
                    flagSemanticError(errorMessage);
                }
            }
            /* Relational operators */
            else if ((syntaxTree->op == GT) || (syntaxTree->op == LT) ||
                     (syntaxTree->op == LTE) || (syntaxTree->op == GTE) ||
                     (syntaxTree->op == EQ) || (syntaxTree->op == NE))
            {
                if ((syntaxTree->child[0]->expressionType == Integer) &&
                    (syntaxTree->child[1]->expressionType == Integer))
                    syntaxTree->expressionType = Integer;
                else
                {
                    sprintf(errorMessage, "relational operators must have "
                                          "integer operands (line %d)\n",
                            syntaxTree->lineno);
                    flagSemanticError(errorMessage);
                }
            }
            else
            {
                sprintf(errorMessage, "error in type checker: unknown operator"
                                      " (line %d)\n",
                        syntaxTree->lineno);
                flagSemanticError(errorMessage);
            }

            break;

        case IdK:

            if (syntaxTree->declaration->expressionType == Integer)
            {
                if (syntaxTree->child[0] == NULL)
                    syntaxTree->expressionType = Integer;
                else
                {
                    sprintf(errorMessage, "identifier is an illegal type "
                                        "(line %d)\n",
                            syntaxTree->lineno);
                    flagSemanticError(errorMessage);
                }
            }
            break;

        case ConstK:

            syntaxTree->expressionType = Integer;
            break;

        case AssignK:

            /* Variable assignment */
            if ((syntaxTree->child[0]->expressionType == Integer) &&
                (syntaxTree->child[1]->expressionType == Integer))
                syntaxTree->expressionType = Integer;
            else
            {
                sprintf(errorMessage, "both assigning and assigned expression"
                                      " must be integer (line %d)\n",
                        syntaxTree->lineno);
                flagSemanticError(errorMessage);
            }

            break;
        }

        break; /* case ExpK */

    } /* switch (syntaxTree->nodekind) */
}

/* dummy do-nothing procedure used to keep traverse() happy */
static void nullProc(TreeNode *syntaxTree)
{
    return;
}

7.3 实验演示

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Scope Identifier        Line   Is a   Symbol type
depth                   Decl.  parm?
--- fibonacci ----------------------------------
  2   cnt                  3     N    Scalar of type integer
  2   firstFib             4     N    Scalar of type integer
  2   secondFib            5     N    Scalar of type integer
  2   fib                  6     N    Scalar of type integer
  1   n                    1     Y    Scalar of type integer
--- main ---------------------------------------
  2   n                   31     N    Scalar of type integer
--- GLOBALS ------------------------------------
  0   input                0     N    Function with return type integer
  0   output               0     N    Function with return type void
  0   fibonacci            1     N    Function with return type integer
  0   main                29     N    Function with return type void
------------------------------------------------