c语言 编译原理（第4版）刘铭 词法分析器

#include <stdio.h> #include <stdlib.h> #include <string.h> #define _KEY_WORD_END "waiting for your expanding" typedef struct { int typenum; char *word; }WORD; char input[255]; char token[255]=""; int p_input; int p_token; char ch; char *rwtab[]={"begin","if","while","do","end",_KEY_WORD_END}; //输入缓冲区中读取一个字符到ch中 char m_getch() { ch=input[p_input]; p_input=p_input+1; return(ch); } //去掉空白符号 void getbc() { while(ch==' '||ch==10) { ch=input[p_input]; p_input=p_input+1; } } //拼接单词 void concat() { token[p_token]=ch; p_token=p_token+1; token[p_token]='\0'; } //判断是否字母 int letter() { if((ch >= 'a' && ch <= 'z' )|| (ch >= 'A' && ch <= 'Z')) return 1; else return 0; } //判断是否数字 int digit() { if(ch >= '0' && ch <= '9') return 1; else return 0; } //检索关键字表格 int reserve() { int i=0; while(strcmp(rwtab[i],_KEY_WORD_END)) { if(!strcmp(rwtab[i],token)) { return i+1; } i=i+1; } return 10; } //回退一个字符 void retract() { p_input=p_input-1; } //数字转换二进制，自己补全 char *dtb() { return NULL; } //读取标识符 WORD *scaner() { WORD *myword=new WORD; myword->typenum=10; myword->word=""; p_token=0; m_getch(); getbc(); if(letter()) { while(letter()||digit()) { concat(); m_getch(); } retract(); myword->typenum=reserve(); myword->word=token; return(myword); } else if(digit()) { while(digit()) { concat(); m_getch(); } retract(); myword->typenum=11; myword->word=token; return(myword); } else switch (ch) { case '=': m_getch(); if (ch == '=') { myword->typenum = 39; myword->word = "=="; return(myword); } retract(); myword->typenum = 21; myword->word = "="; return(myword); break; case '+': myword->typenum = 22; myword->word = "+"; return(myword); break; case '-': myword->typenum = 23; myword->word = "="; return(myword); break; case '*': myword->typenum = 24; myword->word = "*"; return(myword); break; case '/': myword->typenum = 25; myword->word = "/"; return(myword); break; case '(': myword->typenum = 26; myword->word = "("; return(myword); break; case ')': myword->typenum = 27; myword->word = ")"; return(myword); break; case '[': myword->typenum = 28; myword->word = "["; return(myword); break; case ']': myword->typenum = 29; myword->word = "]"; return(myword); break; case '{': myword->typenum = 30; myword->word = "{"; return(myword); break; case '}': myword->typenum = 31; myword->word = "}"; return(myword); break; case ',': myword->typenum = 32; myword->word = ","; return(myword); break; case ':': m_getch(); if(ch=='=') { myword->typenum=18; myword->word=":="; return(myword); } myword->typenum = 33; myword->word = ":"; return(myword); break; case ';': myword->typenum = 34; myword->word = ";"; return(myword); break; case '>': m_getch(); if (ch == '=') { myword->typenum = 37; myword->word = ">="; return(myword); } retract(); myword->typenum = 35; myword->word = ">"; return(myword); break; case '<': m_getch(); if (ch == '=') { myword->typenum = 38; myword->word = ">="; return(myword); } retract(); myword->typenum = 36; myword->word = "<"; return(myword); break; case '!': m_getch(); if (ch == '=') { myword->typenum = 40; myword->word = "!="; return(myword); } retract(); myword->typenum = -1; myword->word = "ERROR"; return(myword); break; case '\0': myword->typenum = 1000; myword->word = "OVER"; return(myword); break; default: myword->typenum = -1; myword->word = "ERROR"; return(myword); break; } } int main() { int over=1; WORD *oneword=new WORD; printf("Enter Your words(end with #):"); scanf("%[^#]s",input); p_input=0; printf("Your words:\n%s\n",input); while(over<1000&&over!=-1) { oneword=scaner(); if(oneword->typenum<1000) printf("(%d,%s)",oneword->typenum,oneword->word); over=oneword->typenum; } printf("\npress#to exit:"); scanf("%[^#]s",input); system("PAUSE"); // }