Question

I normally work in Objective-C, but am now trying to integrate some C code which I don’t know as well.

Let’s start with my Buffer object:

@interface Buffer : NSObject {

    int*  buffer_;
    int   numFrames_;
    int   idNumber_;
}

@property (nonatomic) int* buffer;
@property (nonatomic) int numFrames;
@property (nonatomic) int idNumber;

In another class I’m trying to dynamically create c arrays and stick them into the buffer of my buffer objects. It should be noted that I don’t know how many buffer objects I will need in advance.

for (i=0; i<[arrayOfFlags count]; i++) {

    NSNumber *flagObject = (NSNumber*)[arrayOfFlags objectAtIndex:i];
    int flagInt = [flagObject integerValue];


    Buffer *snippetBuffer = [[Buffer alloc] init];
    int returnArray[44000];
    snippetBuffer.buffer = returnArray;
    snippetBuffer.numFrames = 44000;
    snippetBuffer.idNumber = i;

    int k;

    // NSLog(@"creating snippet buffer at flag %d", flagInt);
    for (k = 0; k < 44000; k++) {

        snippetBuffer.buffer[k] = // insert some values here. 
    }
}

When I run this code all the buffer objects have the same data as the last one to be produced. I think what is happening is that the returnArray being overwritten at each iteration.

So how do I ensure that new memory is being allocated each time I instantiate a c array in a loop? (If that is indeed my problem).

Hope this question wasn’t too complicated. Please feel free to ask questions.

Answer 1

int returnArray[44000];
snippetBuffer.buffer = returnArray;

This is a wrong initialization for your snippetBuffer.buffer pointer, since returnArray is a local variable and gets destroyed at the end of the scope.

Use instead

snippetBuffer.buffer = (int*)malloc(44000*sizeof(int));

Remember to call free to release the memory after you have done.