Question

in my app I create an unsigned char pointer using this function:

- (unsigned char*)getRawData
{
// First get the image into your data buffer
CGImageRef image = [self CGImage];
NSUInteger width = CGImageGetWidth(image);
NSUInteger height = CGImageGetHeight(image);

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

unsigned char *rawData = malloc(height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);

CGContextSetBlendMode(context, kCGBlendModeCopy);

CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), image);
CGContextRelease(context);

// Now your rawData contains the image data in the RGBA8888 pixel format.

return rawData;
}

And in another class I assign a property to that pointer like so: self.bitmapData = [image getRawData];

Where in this process can I free that malloc’d memory? When I try to free the property in dealloc, it gives me an exc_bad_access error. I feel like I’m missing a fundamental c or objective-c concept here. All help is appreciated.

Answer 1

There is a good discussion about the safety of using malloc/free in objective-c here.

As long as you correctly free() the memory that you malloc(), there should be no issue.

I personally think that using NSMutableData or NSMutableArray is just easier. If you don’t need ultimate performance, I would not use the C malloc/free statements directly.