ESP32无法从基于Regexp掩码的字符串中提取字符串

#include <Arduino.h>
#include <regex.h>

void setup() {
  Serial.begin(115200);
  delay(1000);

  // 原始字符串
  const char* input = "Hello, World! This is a test string.";

  // 正则表达式模式
  const char* pattern = "([a-zA-Z]+)";

  // 创建正则表达式对象
  regex_t regex;
  regmatch_t matches[2];

  // 编译正则表达式
  int ret = regcomp(&regex, pattern, REG_EXTENDED);
  if (ret != 0) {
    Serial.println("Failed to compile regex pattern.");
    return;
  }

  // 执行正则表达式匹配
  ret = regexec(&regex, input, 2, matches, 0);
  if (ret == 0) {
    // 提取匹配到的子字符串
    for (int i = 0; i < 2; i++) {
      if (matches[i].rm_so == -1) {
        break;
      }
      int start = matches[i].rm_so;
      int end = matches[i].rm_eo;
      char extracted[end - start + 1];
      strncpy(extracted, input + start, end - start);
      extracted[end - start] = '\0';
      Serial.println(extracted);
    }
  } else if (ret == REG_NOMATCH) {
    Serial.println("No match found.");
  } else {
    Serial.println("Regex match failed.");
  }

  // 释放正则表达式对象
  regfree(&regex);
}

void loop() {
  // 程序循环体
}