[C] help with string handling memory leak Post: 302292500

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Top Forums Programming [C] help with string handling memory leak Post 302292500 by shamrock on Saturday 28th of February 2009 08:19:41 AM

02-28-2009

Registered User

Quote:

Originally Posted by VRoemer

Oh, thats interesting I don't remember leaving that there. Thanks for catching that. ok

I was referring to this code...

Code:

s = strdup( data+20 );  /* don't need both strcpy and strdup */
strcpy(s, data+20);     /* get rid of the strcpy */

Quote:

Originally Posted by VRoemer

Ok then, I have a small question to impose onto this then. If I add this to the very end of the function. Why does it cause a memory leak?

Code:

    free(s); 
    s = NULL;

    s = strdup( data+19 );
    while((*s) && (*s != '\n'))
    {
        s++;
    }
    s++; // skip the newline
    printf( "%s", s);
    free(s);

is it because I reasign s? Becuase I reuse data? If always crashes on that final 'free'

valgrind reports, with and without the final free, a loss of the same amount of bytes.

Yes it's because free expects the exact same pointer that was returned by the call to strdup. By incrementing s you lost the original pointer returned by strdup.

Quote:

Originally Posted by VRoemer

EDIT:
I think I know why, because I moved the pointer right? The fix would be to make an aditional pointer to point at the beginning i believe.

That's right create another pointer that points to the same place as s and increment that one instead of s. This way you won't have any problems when you try to free s.

shamrock

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