一、簡介

       標準的C和C++不支援正則表示式，但有一些函式庫可以輔助C/C++程式設計師完成這一功能。正則表示式常用函式：編譯正則表示式 regcomp()、匹配正則表示式 regexec()、釋放正則表示式 regfree()。

二、詳解

1、程式碼

regcomp.cpp：

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <regex.h>
#include <assert.h>
#include <string.h>
using namespace std;

int find_first(string input, string pattern, string &out){
    regex_t reg;
    regmatch_t pm[1];
    int  iret = 0;
    out = "";
    /*編譯正則表示式*/
    iret = regcomp(&reg, pattern.c_str(), REG_EXTENDED|REG_NEWLINE);
    if (iret != 0){
        return -1;
    }
    iret = regexec(&reg, input.c_str(), 1, pm, 0);
    if (iret == REG_NOMATCH){
        out = "";
        iret = input.length();
    }else if (iret != 0) {
        return -2;
    }else{
        out = input.substr(pm[0].rm_so,pm[0].rm_eo-pm[0].rm_so);
        iret = pm[0].rm_eo;
    }
    regfree(&reg);
    return iret;
}

int find_first(char *buff, char *pattern, char *outdata){
    regex_t reg;
    regmatch_t pm[1];
    int  status = 0;
    /*編譯正則表示式*/
    status = regcomp(&reg, pattern, REG_EXTENDED|REG_NEWLINE);  //擴充套件正則表示式和識別換行符
    if (status != 0){    //成功返回0
        return -1;
    }
    status = regexec(&reg, buff, 1, pm, 0);
    if (status == REG_NOMATCH){
        printf("no match!\n");
        status = -1;
    }
    else if (status != 0) {
        return -2;
    }
    else if (status == 0) {
        int i, j;
        for (i = pm[0].rm_so, j = 0; i < pm[0].rm_eo; i++, j++) {
            outdata[j] = buff[i];
        }
        outdata[i] = '\0';
    }
    regfree(&reg);
    return status;
}

int find_all(char *buff, char *pattern, char result[][20]){   //返回匹配個數
    regex_t reg;
    regmatch_t pm[1];
    int  status = 0;
    char * p = buff;
    int count = 0;
    /*編譯正則表示式*/
    status = regcomp(&reg, pattern, REG_EXTENDED|REG_NEWLINE);  //擴充套件正則表示式和識別換行符
    if (status != 0){    //成功返回0
        return -1;
    }
    int i = 0, j, k;
    while((status = regexec(&reg, p, 1, pm, 0)) == 0) {
        for(j = pm[0].rm_so, k = 0; j < pm[0].rm_eo; j++) {
            result[i][k++] = p[j];
        }
        result[i][k] = '\0';
        i++;
        p += pm[0].rm_eo;
        count++;
        if (*p == '\0')  break;
    }
    regfree(&reg);
    return count;
}
int print_file(const char *file_name, const char *pattern)
{
    regex_t reg;
    regmatch_t pm[1];
    int  status = 0;
    int count = 0;
    FILE *fp = fopen(file_name, "r+");
    assert(fp);
    char buff[1024] = {0};
    char output[1024] = {0};
    /*編譯正則表示式*/
    status = regcomp(&reg, pattern, REG_EXTENDED|REG_NEWLINE);  //擴充套件正則表示式和識別換行符
    assert(status == 0);
    while(fgets(buff, sizeof(buff), fp)) {     //迴圈讀取檔案
        char * p = buff;
        while(1) {
            status = regexec(&reg, p, 1, pm, 0);
            if (status == 0) {  //匹配成功
                count++;
                strncpy(output, p + pm[0].rm_so, pm[0].rm_eo - pm[0].rm_so);
                cout<<"匹配:"<<output<<endl;
                p += pm[0].rm_eo;
            }
            else {
                break;
            }
        }
    }
    regfree(&reg);
    return count;
}
int main()
{
    char result[20][20] = {0};
    char buf[] = "1231a4568b789c234";
    char pattern[] = "[0-9]{3}";

    char resultfirst[20] = {0};
    find_first(buf, pattern, resultfirst);
    cout<<strlen(resultfirst) << ":" << resultfirst<<endl;
    cout << "***************************" <<endl;

    int count = find_all(buf, pattern, result);
    for (int i = 0; i < count; i++) {
        cout<<"result:"<<"i="<<i+1<<"----"<<result[i]<<endl;
    }
    cout << "***************************" <<endl;
    count = print_file("test.txt", "[0-9]{5}");
    cout<<"匹配的個數:"<<count<<endl;
    return 0;
}
 

2、編譯執行

g++ -o regcomp regcomp.cpp
./regcomp

abc12345678
ddd55555555hhh
123456

三、總結