实验目的】
通过上机实验，加深对语法制导翻译的理解，掌握将语法分析所识别的语法成分变换为中间代码的语义翻译方法。
【实验内容】
对给定的程序通过语义分析器能够判断语句串是否正确。正确则输出三地址指令形式的四元式代码，错误则抛出错误信息。
【设计思想】
（1）输入待分析的字符串。
语法如下：
a.关键字：begin,if,then,while,do,end.
b.运算符和界符：:= + - * / < <= > >= <> = ; ( ) #
c.其他单词是标识符(ID)和整形常数(NUM)：ID=letter(letter|digit)*，NUM=digitdigit*
d.空格由空白、制表符和换行符组成。空格一般用来分隔ID、NUM、运算符、界符和关键字，词法分析阶段通常被忽略。
（2）扫描字符串，采用递归向下进行分析。
主要函数如下：
a.scaner()//词法分析函数，char token[8]用来存放构成单词符号的字符串;
b.parser()//语法分析，在语法分析的基础上插入相应的语义动作：将输入串翻译成四元式序列。只对表达式、赋值语句进行翻译。
c.emit(char *result,char *arg1,char *op,char *ag2)//该函数功能是生成一个三地址语句返回四元式表中。
d.char *newtemp()//该函数返回一个新的临时变量名，临时变量名产生的顺序为T1,T2,…。
【实验要求】
四元式表的结构如下：
struct {char result[8];
char ag1[8];
char op[8];
char ag2[8];
}quad[20];
（3）输出为三地址指令形式的四元式序列。
例如：语句串begin a:=2+3*4;x:=(a+b)/c;end#，
输出的三地址指令如下：
t1=3*4
t2=2+t1
a=t2
t3=a+b
t4=t3/c
x=t4
代码：
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#include "stdio.h"#include "string.h"char prog[100], token[8], ch;char *rwtab[6] = { "begin", "if", "then", "while", "do", "end" };int syn, p, m, n, sum, q;int kk;struct {char result1[8];char ag11[8];char op1[8];char ag21[8];} quad[20];char *factor();char *expression();int yucu();char *term();int statement();int lrparser();char *newtemp();scaner();emit(char *result, char *ag1, char*op, char *ag2); main(){int j;q = p = kk = 0;printf("\n**************************************");printf("\nplease input a string (end with'#'): ");do{scanf_s("%c", &ch);prog[p++] = ch;} while (ch != '#');p = 0;scaner();lrparser();if (q>19)printf(" too longsentense!\n");else for (j = 0; j<q; j++)printf(" %s = %s%s %s \n\n", quad[j].result1, quad[j].ag11, quad[j].op1, quad[j].ag21);getchar();} int lrparser(){int schain = 0;kk = 0;if (syn == 1){scaner();schain = yucu();if (syn == 6){scaner();if ((syn == 0) && (kk == 0)) printf("Success!\n");}else {if (kk != 1)printf("short of 'end'!\n");kk = 1;getchar();exit(0);}}else {printf("short of 'begin' !\n");kk = 1;getchar();exit(0);}return (schain);} int yucu(){int schain = 0;schain = statement();while (syn == 26){scaner();schain = statement();}return (schain);} int statement(){char tt[8], eplace[8];int schain = 0;if (syn == 10){strcpy_s(tt, 255, token);scaner();if (syn == 18){scaner();strcpy_s(eplace, 255, expression());emit(tt, eplace, "", "");schain = 0;}else {printf("short of sign ':='!\n");kk = 1;getchar();exit(0);}return (schain);}} char *expression(){char *tp, *ep2, *eplace, *tt;tp = (char *)malloc(12);ep2 = (char *)malloc(12);eplace = (char *)malloc(12);tt = (char *)malloc(12);strcpy_s(eplace, 255, term());while ((syn == 13) || (syn == 14)){if (syn == 13)strcpy_s(tt, 255, "+");else strcpy_s(tt, 255, "-");scaner();strcpy_s(ep2, 255, term());strcpy_s(tp, 255, newtemp());emit(tp, eplace, tt, ep2);strcpy_s(eplace, 255, tp);}return (eplace);} char *term(){char *tp, *ep2, *eplace, *tt;tp = (char *)malloc(12);ep2 = (char *)malloc(12);eplace = (char *)malloc(12);tt = (char *)malloc(12);strcpy_s(eplace, 255, factor());while ((syn == 15) || (syn == 16)){if (syn == 15)strcpy_s(tt, 255, "*");else strcpy_s(tt, 255, "/");scaner();strcpy_s(ep2, 255, factor());strcpy_s(tp, 255, newtemp());emit(tp, eplace, tt, ep2);strcpy_s(eplace, 255, tp);}return (eplace);} char *factor(){char *fplace;fplace = (char *)malloc(12);strcpy_s(fplace, 255, "");if (syn == 10){strcpy_s(fplace, 255, token);scaner();}else if (syn == 11){itoa(sum, fplace, 10);scaner();}else if (syn == 27){scaner();fplace = expression();if (syn == 28) scaner();else {printf("error on ')'!\n");kk = 1;getchar();exit(0);}}else {printf("error on '(' !\n");kk = 1;getchar();exit(0);}return (fplace);} char *newtemp(){char *p;char m[8];p = (char *)malloc(8);kk++;itoa(kk, m, 10);strcpy_s(p + 1, 255, m);p[0] = 't';return(p);} scaner(){sum = 0;for (m = 0; m<8; m++)token[m++] = NULL;m = 0;ch = prog[p++];while (ch == ' ')ch = prog[p++];if (((ch <= 'z') && (ch >= 'a')) || ((ch <= 'Z') && (ch >= 'A'))){while (((ch <= 'z') && (ch >= 'a')) || ((ch <= 'Z') && (ch >= 'A')) || ((ch >= '0') && (ch <= '9'))){token[m++] = ch;ch = prog[p++];}p--;syn = 10;token[m++] = '\0';for (n = 0; n<6; n++)if (strcmp(token, rwtab[n]) == 0){syn = n + 1;break;}}else if ((ch >= '0') && (ch <= '9')){while ((ch >= '0') && (ch <= '9')){sum = sum * 10 + ch - '0';ch = prog[p++];}p--;syn = 11;}else switch (ch){case '<':m = 0;ch = prog[p++];if (ch == '>'){syn = 21; }else if (ch == '='){syn = 22;}else{syn = 20;p--;}break;case '>':m = 0;ch = prog[p++];if (ch == '='){syn = 24;}else{syn = 23;p--;}break;case ':':m = 0;ch = prog[p++];if (ch == '='){syn = 18;}else{syn = 17;p--;}break;case '+': syn = 13; break;case '-': syn = 14; break;case '*': syn = 15; break;case '/': syn = 16; break;case '(': syn = 27; break;case ')': syn = 28; break;case '=': syn = 25; break;case ';': syn = 26; break;case '#': syn = 0; break;default: syn = -1; break; }} emit(char *result, char *ag1, char*op, char *ag2){strcpy_s(quad[q].result1, 255, result);strcpy_s(quad[q].ag11, 255, ag1);strcpy_s(quad[q].op1, 255, op);strcpy_s(quad[q].ag21, 255, ag2);q++;} |
运行截图：
