CODEWITHSUNDEEP
c++objective-ccaudiocore-audio
manderson
manderson

Reputation: 676

C array with float data crashing in Objective C class (EXC_BAD_ACCESS)

I am doing some audio processing and therefore mixing some C and Objective C. I have set up a class that handles my OpenAL interface and my audio processing. I have changed the class suffix to

.mm

...as described in the Core Audio book among many examples online.

I have a C style function declared in the .h file and implemented in the .mm file:

static void granularizeWithData(float *inBuffer, unsigned long int total) {

    // create grains of audio data from a buffer read in using ExtAudioFileRead() method.

    // total value is: 235377
    float tmpArr[total];

    // now I try to zero pad a new buffer:
    for (int j = 1; j <= 100; j++) {
        tmpArr[j] = 0;
        // CRASH on first iteration EXC_BAD_ACCESS (code=1, address= ...blahblah)
    }
}

Strange??? Yes I am totally out of ideas as to why THAT doesn't work but the FOLLOWING works:

    float tmpArr[235377];

    for (int j = 1; j <= 100; j++) {
        tmpArr[j] = 0;
        // This works and index 0 - 99 are filled with zeros
    }

Does anyone have any clue as to why I can't declare an array of size 'total' which has an int value? My project uses ARC, but I don't see why this would cause a problem. When I print the value of 'total' when debugging, it is in fact the correct value. If anyone has any ideas, please help, it is driving me nuts!

Upvotes: 1

Views: 1102

Answers (1)

Jack
Jack

Reputation: 133577

Problem is that that array gets allocated on the stack and not on the heap. Stack size is limited so you can't allocate an array of 235377*sizeof(float) bytes on it, it's too large. Use the heap instead:

float *tmpArray = NULL;

tmpArray = (float *) calloc(total, sizeof(float)); // allocate it

// test that you actually got the memory you asked for

if (tmpArray)
{
  // use it

  free(tmpArray); // release it
}

Mind that you are always responsible of freeing memory which is allocated on the heap or you will generate a leak.

In your second example, since size is known a priori, the compiler reserves that space somewhere in the static space of the program thus allowing it to work. But in your first example it must do it on the fly, which causes the error. But in any case before being sure that your second example works you should try accessing all the elements of the array and not just the first 100.

Upvotes: 6

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