CODEWITHSUNDEEP
iosc
spring
spring

Reputation: 18517

"Call to 'malloc' has an allocation size of 0 bytes" error when size is passed?

I've seen there are questions about malloc(0) which yield this alert about allocation size. My question is that I am getting this alert with a size.

In my code:

I get the alert on the line below. Before that line I check that midiFileEventCount is non-zero. My app seems to run correctly. Am I doing something wrong here?

This is on iOS 7.1 

midiFileEvents=(BASS_MIDI_EVENT*)malloc(midiFileEventCount*sizeof(BASS_MIDI_EVENT));

Log statements:

printf("midiFileEventCount %u \n", midiFileEventCount);
printf("BASS_MIDI_EVENT size: %lu \n", sizeof(BASS_MIDI_EVENT));
printf("midiFileEvents size: %lu \n", midiFileEventCount*sizeof(BASS_MIDI_EVENT));

Output:

midiFileEventCount 1684 
BASS_MIDI_EVENT size: 20 
midiFileEvents size: 33680

Upvotes: 0

Views: 2254

Answers (1)

Jesse Rusak
Jesse Rusak

Reputation: 57188

So, this is probably a potential bug in your code. The analyzer is telling you that there is a possible code path in your function in which the size is zero. Consider the following methods:

- (void *)foo:(int)size {
    return malloc(size);
}

- (void *)bar:(int)size {
    if (size == 0) {
        NSLog(@"got zero size!");
    }
    return malloc(size);
}

The first method will produce no analyzer results. The second will produce the same diagnostic you're seeing. The clang folks reason as follows: normally, a call to malloc will probably not have a zero size passed, so foo is unlikely to be a problem. bar, however, explicitly checks for a size of zero, and then continues to the malloc anyway. So, since you (the code writer) are clearly expecting that the size might be zero, it warns you that, in that case, you're mallocing zero bytes. (If you expand the diagnostic, it will show you exactly what assumptions it's making that are leading to a zero-sized allocation).

Of course, it's possible that you never actually call that method such that it produces a zero-sized malloc, but the analyzer only looks over smaller regions of code and notices "suspicious" patterns.

In the case of bar above, you could resolve it by asserting or returning NULL in the case that zero is passed.

Upvotes: 3

Related Questions