正则表达式匹配算法

#include <iostream>
#include<String>
#include<stdio.h>
using namespace std;

int match(char * regexp,char * text);
int matchhere(char * regexp,char * text);
int matchstar(int c,char *regexp,char * text);

/* match: 在text中查找regexp */
int match(char * regexp,char * text){
    if(regexp[0] == '^'){
        return matchhere(regexp + 1,text);
    }
    do{/* 即使字符串为空时也必须检查 */
        if(matchhere(regexp,text)){
            return 1;
        }
    }while(*text++ != '');
    return 0;
}
/* matchhere: 在text中的开头查找regexp */
int matchhere(char * regexp,char * text){
    if(regexp[0] == ''){
        return 1;
    }
    if(regexp[1] == '*'){
        return matchstar(regexp[0],regexp + 2,text);
    }
    if(regexp[0] == '$' && regexp[0] == ''){
        return *text == '';
    }
    if(*text != '' && (regexp[0] == '.' || regexp[0] == *text)){
        return matchhere(regexp + 1,text + 1);
    }
    return 0;
}

/* matchstar: 在text的开头查找C*regexp */
int matchstar(int c,char * text){
    do{/* 通配符*匹配零个或者多个实例*/
        if(matchhere(regexp,text)){
            return 1;
        }
    }while(*text != '' && (*text++ == c || c == '.'));
    return 0;
}

int main()
{
    char * StrSource = "Plastic We use plastic wrap to protect our foods. We put our garbage in plastic bags or plastic cans. We sit on plastic chairs,play with plastic toys,drink from plastic cups,and wash our hair with shampoo from plastic bottles!Plastic does not grow in nature. It is made by mixing certain things together. We call it a produced or manufactured material. Plastic was first made in the 1860s from plants,such as wood and cotton. That plastic was soft and burned easily.";
    char mystr[50];
    while(true){
        scanf("%s",mystr);
        if(match(mystr,StrSource)){
            cout<<"匹配成功！"<<endl;
        }else{
            cout<<"匹配失败！"<<endl;
        }
    }
    return 0;
}

（编辑：李大同）

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