Implementing qsort in Objective-C - objective-c

Question

I'm trying to use qsort to sort a C array in descending order based on what this website is suggesting.
Here is the relevant code:
int x = 3;
- (IBAction)CaptureButton:(id)sender
{
x++;
if (x % 3 == 1)
{
int areas[detectedBlobs.size()];
for (int i = 0; i < detectedBlobs.size(); i++)
{
areas[i] = detectedBlobs[i].getWidth() * detectedBlobs[i].getHeight();
}
int compareInts(void const *item1, void const *item2)
{ // first error
int const *int1 = item1;
int const *int2 = item2;
return (*int2 - *int1);
}
qsort(areas, detectedBlobs.size(), sizeof(int), compareInts); // second error
}
}
Here are the two errors I'm getting:
First error:
Function definition is not allowed here
Second error:
Use of undeclared identifier 'compareInts'
If I cannot define the comparator (compareInts) function here, where do I have to define it? Also, how can I get the qsort function to recognize the comparator?

Answer 1

Objective-C does not allow function definitions inside methods. Move compareInts outside of the method, and make it static to hide from other translation units:
static int compareInts(const void* item1, const void* item2) {
const int* int1 = (const int*)item1;
const int* int2 = (const int*)item2;
return (*int2 - *int1);
}
- (IBAction)CaptureButton:(id)sender {
x++;
if (x % 3 == 1) {
int areas[detectedBlobs.size()];
for (int i = 0; i < detectedBlobs.size(); i++) {
areas[i] = detectedBlobs[i].getWidth() * detectedBlobs[i].getHeight();
}
qsort(areas, detectedBlobs.size(), sizeof(int), compareInts);
}
}