Thread: strftime makes together with calloc an error: realloc(): invalid next size

  1. #1
    Registered User
    Join Date
    Dec 2018

    strftime makes together with calloc an error: realloc(): invalid next size


    It would be great if someone could help me with this problem.

    #define MAX_ELEMENTS 1000
    #define MAX_ELEMENTS_TIME 40
    time_t rawtime;
    struct tm* time_info;
    char buffer_filedate[MAX_ELEMENTS_TIME];
    time_info = localtime(&rawtime);
    int number_of_char;
    number_of_char = strftime(buffer_filedate,MAX_ELEMENTS_TIME,"%d.%B%Y/%H:%M_Uhr", time_info);
    The prog works fine. But as soon as "buffer_filedate"

    console_output_string = (char *) realloc(console_output_string, (sizeof(console_output_string)+sizeof(buffer_filedate)));
    is attached to an array dynamically the compiler tells me: "realloc(): invalid next size"

    If i change strftime() format, for example to:
    number_of_char = strftime(buffer_filedate,MAX_ELEMENTS_TIME,"%d.%B%Y/%H:%M", time_info);
    everything works fine.

    I did not read anything, that this minimal difference (Line 11 of first code-snippet vs Line1 of the third code-snippet) in the function strftime() could be invalid.

    Sorry for my bad english. I try my best to get better!!
    Last edited by PhoenixStefan; 01-29-2019 at 06:24 PM. Reason: wrong language

  2. #2
    Registered User
    Join Date
    Dec 2018
    Problem solved!
    The programm used sizeof(console_output_string) multiple times before code-snippet 2. But console_output_string is a dynamically constructed array. And: sizeof() can not return the size of a dynamically allocated buffer. It was not a problem with strftime() directly, the length of the computed format-char only made this problem visible.

    Thank you all for reading.

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