简单的词法分析器分离出保留字、标识符字符串、常量、算符、和界符

#include<iostream.h> #include<string.h> char *KeyWord[45]={"auto","break","case","char","const","continue","default","do","double","else","enum","extern","float","for","goto","if","int","long","return","short","signed","sizeof","static","struct","switch","typedef","unsigned","void","while","catch","class","const_cast","delete","friend","inline","new","operator","private","protected","public","template","this","throw","try","virtual"}; int i=0,j=0,k=0,t=0;//搜索指示器 char ch;//存放最新读入的原程序字符 char strToken[20];//存放构成单词符号的字符串 char * chr_form[100];//字符表 char * int_form[100];//常数表 char form[1000]; int q=0; int temp; void GetChar()//将下一个字符读入ch中,搜索指示器前移一字符位 { ch=form[k]; k++; } void GetBC()//检查ch中的字符是否为空白,若是则调用Getchar直至ch中进入 //一个非空白字符 { while(ch==' ') { //k--; GetChar(); } } void Concat()//将ch中的字符连接到strToken之后, { strToken[i]=ch; i++; } bool IsLetter()//判断ch中的字符是否为字符 { if(((ch<='z')&&(ch>='a'))||((ch<='Z')&&(ch>='A'))) return (1); else return(0); } bool IsDigit()//判断ch中的字符是否为数字 { //k--; if(((ch)<='9')&&( (ch)>='0')) return (1); else return (0); } int Reserve()//对strToken中的字符串查找保留字表,若它是一个保留字 //则返回它的编码,否则返回-1值 { for(int q=0;q<45;q++) { if (strcmp(KeyWord[q],strToken)==0) return q; if(q==44) return -1; } } void Retract()//将搜索指示器回调一个字符位置,将ch置为空白字符 { k--; ch=NULL; } char*InsertId()//将strToken中的标识符插入符号表,返回符号表的指针 { chr_form[j]=strToken; j++; return chr_form[0]; } char * InsertConst()//将strToken中的常数插入常数表,返回常数表指针 { int_form[t]=strToken; t++; return int_form[0]; } int code; ////////////////////////////////////////////////////////////////////// void analyze() { GetChar(); GetBC(); //cout<<"此处没有错"<<endl; if(IsLetter()) { while(IsLetter()||IsDigit()) { Concat(); GetChar(); } //cout<<"此处没有错"<<endl; Retract(); code=Reserve(); switch(code) { case -1:cout<<"字符串, "<<strToken<<endl;break; default:cout<<"关键字, "<<strToken<<endl; } } else { if(IsDigit()) { while(IsDigit()||ch=='.') { Concat(); GetChar(); } Retract(); cout<<"常数, "<<strToken<<endl; } else { switch (ch) { case '=': case '/': case '%': case '*':cout<<"运算符，"<<ch<<endl;break; case '-': GetChar(); if(ch=='-') { cout<<"运算符，"<<"--"<<endl;break; } else { Retract(); cout<<"运算符，"<<"-"<<endl;break; } case '+': GetChar(); if(ch=='+') { cout<<"运算符，"<<"++"<<endl;break; } else { Retract(); cout<<"运算符，"<<"+"<<endl;break; } case '|': GetChar(); if(ch=='|') { cout<<"运算符，"<<"||"<<endl;break; } else { Retract(); cout<<"非法符号，"<<"|"<<endl;break; } case '&': GetChar(); if(ch=='&') { cout<<"运算符，"<<"&&"<<endl;break; } case '(': case ';': case ')': case ':': case'[': case']': case '"': case'\'': case '{': case ',': case '}':cout<<"界符， "<<ch<<endl;break; case '<': GetChar(); if(ch=='<') { cout<<"运算符，"<<"<<"<<endl;break; } else { cout<<"界符， "<<"<"<<endl;break; } case '>': GetChar(); if(ch=='>') { cout<<"运算符，"<<">>"<<endl;break; } else { Retract(); cout<<"界符， "<<">"<<endl;break; } } } } while(k<q) { // strcpy(strToken," "); //strcpy(strToken,"\0"); for(int p=0;p<50;p++) strToken[p]='\0'; i=0; analyze(); } } void main() { cout<<"请输入一段程序，以#号结束："<<endl; form[0]=cin.get(); for( q=1;form[q-1]!='##';q++) { form[q]=cin.get(); if(form[q]=='#') { cout<<"你输入的程序段为\n"; cout.write(form,q); break; } } cout<<endl; analyze(); }