time_t troubles

This is a discussion on time_t troubles within the C++ Programming forums, part of the General Programming Boards category; I have a string with the following contents: "1950-01-01 00:00:00". I have the following code. It should create a time_t ...

  1. #1
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    time_t troubles

    I have a string with the following contents: "1950-01-01 00:00:00".

    I have the following code. It should create a time_t object from the string. But it crashes and I don't understand why..
    Code:
    tm dbTime;
    dbTime.tm_year = atoi((s.substr(0, 4)).c_str()) - 1900;
    dbTime.tm_mon = atoi((s.substr(5, 2)).c_str());
    dbTime.tm_mday = atoi((s.substr(8, 2)).c_str());
    dbTime.tm_hour = atoi((s.substr(11,2)).c_str());
    dbTime.tm_min = atoi((s.substr(14, 2)).c_str());
    dbTime.tm_sec = atoi((s.substr(7, 2)).c_str());
    dbTime.tm_isdst = false;
    
    // Seems to be correct:
    cout << "datetime values read: " << endl;
    cout << dbTime.tm_year << endl;
    cout << dbTime.tm_mon << endl;
    cout << dbTime.tm_mday << endl;
    cout << dbTime.tm_hour << endl;
    cout << dbTime.tm_min << endl;
    cout << dbTime.tm_sec << endl;
    cout << dbTime.tm_isdst << endl;
    
    
    time_t t = mktime(&dbTime);  // returns  -1, error code
    cout << ctime(&t) << endl;     // crashes
    Why does mktime return -1? Is something wrong with the tm instance?

    I wasn't sure where to post this. If it should be in the C subforum, please move it there.

    Thanks

  2. #2
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    Perhaps because in most implementations, time_t starts from 1-Jan-1970. That's not guaranteed, but it's certainly quite common.

    ctime shouldn't crash - that would probably be a consequence of the bad value tho'.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
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    Thanks, matsp!

    I knew about the 1 jan 1970 thing, but somehow it didn't occur to me when debugging this problem.. Thanks for pointing that out.

  4. #4
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by C+/-
    I have a string with the following contents: "1950-01-01 00:00:00".
    Code:
    dbTime.tm_sec = atoi((s.substr(7, 2)).c_str());
    Typo? s.substr(7,2) is "-0". Is this actually s.substr(17,2) instead?
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
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