Should we check if memory allocations fail?

Question

I've seen a lot of code that checks for NULL pointers whenever an allocation is made. This makes the code verbose, and if it's not done consistently, only when the programmer felt like it, doesn't even ensure that the program won't crash when the address space runs out. Besides, if the program can't make more allocations, it wouldn't be able to do its function anyway, right?

So my question is, isn't it better for most programs not to check at all and just let the program crash if memory runs out? At least the code is more readable that way.

Note

I'm talking about desktop apps that run on modern computers (at least 2 GB address space), and that most definitely don't operate space shuttles, life support systems, or BP's oil platforms. Most importantly I'm talking about programs that use malloc but never really go above 5 MB of memory usage.

Answer 1

Always check the return value, but for clarity, it's common to wrap malloc() in a function which never returns NULL:

void *
emalloc(size_t amt){
    void *v = malloc(amt);  
    if(!v){
        fprintf(stderr, "out of mem\n");
        exit(EXIT_FAILURE);
    }
    return v;
}

Then, later you can use

char *foo = emalloc(56);
foo[12] = 'A';

With no guilty conscience.

Answer 2

Yes, you should check for a null return value from malloc. Even if you can't recover from the failure of memory allocation you should explicitly exit. Carrying on as though memory allocation had succeeded leaves your application in an inconsistent state and is likely to cause "undefined behavior" which should be avoided.

For example, you may end up writing inconsistent data to external storage which may hinder the ability of the next run of the application to recover. It's much safer to exit swiftly in a more controlled fashion.

Many applications that want to exit on allocation failure wrap malloc in a function that checks the return value and explicitly aborts on failure.

Arguably, this is one advantage of the C++ default new approach to throw an exception on allocation failure. It requires no effort to exit on memory allocation failure.