在 C++ 中使用 mktime 和 timegm 函数的月份自动增量

问：

我想使用 C++ 将字符串日期 （UTC） 转换为时间戳。 它工作正常，除了月份，它会自动递增 1。

如果字符串为 ，则时间戳将为 ，即 的时间戳。202212220746482022-12-22 07:46:4816743736082023-01-22 07:46:48

我不明白这种自动递增的原因，因为下面的代码中没有月份变量的变化。

    cout << "date : " << receivedDate << endl;
    struct tm t;
    time_t timestamp;
    size_t year_size = 4;
    size_t other_size = 2;
    t.tm_year = stoi(receivedDate.substr(0, 4), &year_size, 10) - 1900;
    t.tm_mon = stoi(receivedDate.substr(4, 2), &other_size, 10);
    t.tm_mday = stoi(receivedDate.substr(6, 2), &other_size, 10);
    t.tm_hour = stoi(receivedDate.substr(8, 2), &other_size, 10);
    t.tm_min = stoi(receivedDate.substr(10, 2), &other_size, 10);
    t.tm_sec = stoi(receivedDate.substr(12, 2), &other_size, 10);
    t.tm_isdst = -1;
    cout << "year : " << t.tm_year + 1900 << "\nmonth : " << t.tm_mon << "\nday : " << t.tm_mday << "\nhour : " << t.tm_hour << "\nminutes : " << t.tm_min << "\nseconds : " << t.tm_sec << endl;

    timestamp = timegm(&t);

    cout << "timestamp : " << timestamp << endl;
    cout << "asctime timestamp : " << asctime(&t);