Thread: Is This Supposed To Happen? [Dynamic Memory]

  1. #1
    Registered User
    Join Date
    Sep 2006

    Is This Supposed To Happen? [Dynamic Memory]

    I'm calling the following function:

    unsigned int Test(void)
        char *var;
        var = (char*) malloc(255);
        strcpy(var,"A string.");
        MessageBox(NULL,var,"Data in var",MB_OK);
        return 0;
    And, for some reason, even though it's been free()'d, I'm still getting this: (see attachment).

    Is this supposed to happen? o_O

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    You can get anything and everything by using freed memory. All this means is that either (a) the memory has yet to be reassigned and/or (b) the new owner hasn't written new stuff in it yet. The memory is not trashed when freed.

  3. #3
    Registered User
    Join Date
    Sep 2006
    Oh, that makes sense. Thanks p_o

  4. #4
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    segmentation fault
    A free pointer still points to the same address. You could use var=NULL.

    ps. your memset does not need to be one byte smaller than your malloc, since they both refer to the number of (not "the count beginning with zero").
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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