编译原理_词法分析

简单的词法分析问题，实现了识别关键字、标识符、数字、运算符、边界符的功能

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#include #include #include #include using namespace std; string temp=""; string s1; string ss=""; string keyword[]={"cin","cout","main","string","if","else","while","do","int","char","double","bool","float","return","long","case","break","continue", "auto","for","goto","const","using","namespace","std"}; string bijiao=">=<"; string bj="()[]{},;"; string ys="+-*/%^&!|"; int getword(int j) { int biao=0; for(int u=j;u { if(s1[u]==' ') break; else if('a'<=s1[u]&&s1[u]<='z'||'A'<=s1[u]&&s1[u]<='Z') { temp=temp+s1[u]; //ss=temp; } else if('0'<=s1[u]&&s1[u]<='9') { cout<<"数字"<<" "< biao=1; //ss=ss+s1[u]; break; } int biao1=0;//比较符的标记； for(int k=0;k { if(bijiao[k]==s1[u]) biao1=1; } if(biao1==1) { cout<<"比较符"<<" "< biao=1; //ss=ss+s1[u]; break; } int biao2=0;//运算符的标记； for(int k=0;k { if(ys[k]==s1[u]) biao2=1; } if(biao2==1) { cout<<"运算符"<<" "< biao=1; //ss=ss+s1[u]; break; } int biao3=0;//边界符的标记； for(int k=0;k { if(bj[k]==s1[u]) biao3=1; } if(biao3==1) { cout<<"边界符"<<" "< biao=1; //ss=ss+s1[u]; break; } } return biao; } int main() { fstream fin1,fin2; fin1.open("1.txt"); fin2.open("2.txt"); int hang=1; while(getline(fin1,s1)) { int l,b; cout< hang++; l=s1.size(); if(l==0) continue; if(s1[0]=='#') {cout< for(int j=0;j { if(s1[j]==' '||s1[j]=='\n'||s1[j]=='\t') { continue; } if('a'<=s1[j]&&s1[j]<='z'||'A'<=s1[j]&&s1[j]<='Z') { b=getword(j); if(b==1) { cout<<"标记符号："<<" "< j=j+temp.size()-1; temp=""; continue; } int biao5=0; for(int k=0;k<25;k++) { if(keyword[k]==temp) { cout<<"特殊符号："<<" "< j=j+temp.size()-1;//因为要j++； break; } else { cout<<"标记符号："<<" "< j=j+temp.size()-1; temp=""; break; } } } } //cout< // ss=""; } }