C语言中正则表达式怎么匹配C语言regex库的函数详解

#include <regex.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  regex_t regex;
  int ret;
  const char *pattern = "hello[[:space:]]+world"; // 匹配 "hello" 后面跟着一个或多个空格，然后是 "world"
  const char *text = "hello   world";

  // 编译正则表达式
  ret = regcomp(&regex, pattern, REG_EXTENDED); // REG_EXTENDED 使用扩展正则表达式语法
  if (ret) {
    fprintf(stderr, "Could not compile regex
");
    exit(1);
  }

  // 执行正则表达式匹配
  ret = regexec(&regex, text, 0, NULL, 0); // 0, NULL, 0 表示我们不关心匹配的细节，只关心是否匹配
  if (!ret) {
    printf("Match found!
");
  } else if (ret == REG_NOMATCH) {
    printf("No match found.
");
  } else {
    char errbuf[100];
    regerror(ret, &regex, errbuf, sizeof(errbuf));
    fprintf(stderr, "Regex match failed: %s
", errbuf);
    exit(1);
  }

  // 释放正则表达式
  regfree(&regex);

  return 0;
}

#include <regex.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  regex_t regex;
  int ret;
  const char *pattern = "a\\b"; // 匹配 "a"
  const char *text = "a\b";

  ret = regcomp(&regex, pattern, 0);
  if (ret) {
    fprintf(stderr, "Could not compile regex
");
    exit(1);
  }

  ret = regexec(&regex, text, 0, NULL, 0);
  if (!ret) {
    printf("Match found!
");
  } else if (ret == REG_NOMATCH) {
    printf("No match found.
");
  } else {
    char errbuf[100];
    regerror(ret, &regex, errbuf, sizeof(errbuf));
    fprintf(stderr, "Regex match failed: %s
", errbuf);
    exit(1);
  }

  regfree(&regex);

  return 0;
}

#include <regex.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  regex_t regex;
  int ret;
  const char *pattern = "hello([[:space:]]+)(world)"; // 匹配 "hello" 后面跟着一个或多个空格，然后是 "world"，并捕获空格和 "world"
  const char *text = "hello   world";
  regmatch_t pmatch[3]; // 我们要捕获 3 个子字符串：整个匹配、空格、"world"
  size_t nmatch = 3;

  ret = regcomp(&regex, pattern, REG_EXTENDED);
  if (ret) {
    fprintf(stderr, "Could not compile regex
");
    exit(1);
  }

  ret = regexec(&regex, text, nmatch, pmatch, 0);
  if (!ret) {
    printf("Match found!
");
    for (int i = 0; i < nmatch; i++) {
      printf("Match %d: start=%ld, end=%ld
", i, (long)pmatch[i].rm_so, (long)pmatch[i].rm_eo);
      if (pmatch[i].rm_so != -1 && pmatch[i].rm_eo != -1) {
          char *substring = (char*)malloc(pmatch[i].rm_eo - pmatch[i].rm_so + 1);
          strncpy(substring, text + pmatch[i].rm_so, pmatch[i].rm_eo - pmatch[i].rm_so);
          substring[pmatch[i].rm_eo - pmatch[i].rm_so] = '';
          printf("Substring %d: %s
", i, substring);
          free(substring);

      }
    }
  } else if (ret == REG_NOMATCH) {
    printf("No match found.
");
  } else {
    char errbuf[100];
    regerror(ret, &regex, errbuf, sizeof(errbuf));
    fprintf(stderr, "Regex match failed: %s
", errbuf);
    exit(1);
  }

  regfree(&regex);

  return 0;
}

#include <regex.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  regex_t regex;
  int ret;
  const char *pattern = "hello[[:space:]+world"; // 错误的正则表达式：缺少一个 ]

  ret = regcomp(&regex, pattern, REG_EXTENDED);
  if (ret) {
    char errbuf[100];
    regerror(ret, &regex, errbuf, sizeof(errbuf));
    fprintf(stderr, "Regex compilation failed: %s
", errbuf);
    exit(1);
  }

  regfree(&regex);

  return 0;
}