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#include<stdio.h> #include<stdlib.h> #include<string.h> #define _KEY_WOED_END "waiting for your expanding" //关键字结束标志
typedef struct { int typenum; char * word; }WORD;
char input[255]; //输入换缓冲区
char token[255]=""; //单词缓冲区
int p_input; //输入换缓冲区指针
int p_token; //单词缓冲区指针
char ch; //当前所读的字符
char *rwtab[]={"begin","if","then","while","do","end",_KEY_WOED_END}; //C语言关键字
WORD * scaner(); //词法扫描函数,获得关键字
main() { int over=1; WORD *oneword; oneword=(WORD *)malloc(sizeof(WORD)); printf("请输入您的字符串(以#作为结束标志):"); scanf("%[^#]s",input); p_input=0; printf("您输入的字符串是:%s\n\n",input); while(over<1000&&over!=-1) { oneword=scaner(); printf("(%d,%s)\n",oneword->typenum,oneword->word); over=oneword->typenum; }
}
//需要用到的自编函数参考实现 //从输入缓冲区读取一个字符到ch中
char m_getch() { ch=input[p_input]; p_input=p_input+1; return (ch); }
//去掉空白字符 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; for(i=0;i<7;i++) { 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; }
void retract() { p_input=p_input-1; }
WORD *scaner() { WORD *myword; myword=(WORD *)malloc(sizeof(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=20; 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=13; myword->word="+"; return(myword); break; case ‘-‘: myword->typenum=14; myword->word="-"; return(myword); break; case ‘*‘: myword->typenum=15; myword->word="*"; return(myword); break; case ‘/‘: myword->typenum=16; 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=17; myword->word=":"; return(myword); break; case ‘;‘: myword->typenum=26; myword->word=";"; return(myword); break; case ‘>‘: myword->typenum=23; myword->word=">"; return(myword); break; case ‘<‘: myword->typenum=20; 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); } } }
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原文地址:http://www.cnblogs.com/dalaotan/p/4878453.html