Thread: Why return malloc'd char array not work, but local char array does?

  1. #1
    Registered User
    Join Date
    Nov 2006

    Why return malloc'd char array not work, but local char array does?

    Inside a function, I create a char array which I pass to a library function that fills it with a value. I then pass this back to the caller. When I do it by creating an array with malloc (and then freeing it outside the function), it only fills the array with the first 3 characters. When i create it as a local array, it works (and simply warns me I'm passing a local array back out).

    //This does NOT Work:
    char* getStringWithMalloc(...elided...)
          char* data = ( char* ) malloc( 256 * sizeof( char ) );
          fillArray( data );
          return data;
    //This DOES work:
    char* getString(...elided...)
          char data[256];
          fillArray( data );
          return data;
    int main(...)
          //Does not work, only grabs first three characters
          char* value = getDataWithMalloc(...);
          printf( value );
          free( value );
          //This DOES work
          printf( getDataWithMalloc(...) );

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    That's weird. Have you tried stepping through with a debugger?

    This thread is clearly of duplicate of this one, hence it is now closed.
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  3. #3
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    I think this is the third thread about the same subject. Maybe we should merge them together.

    Compilers can produce warnings - make the compiler programmers happy: Use them!
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  4. #4
    Cat without Hat CornedBee's Avatar
    Join Date
    Apr 2003

    The first one should work, but has a horrible interface.
    The second is simply broken. Deadly, even.

    Whatever error you're seeing, though, it's got to be in fillArray.

    Also, this is pretty much C.
    All the buzzt!

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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