Logging memory allocation errors

Question

Let's say I'm trying to write a checked version of malloc() in C99 - nothing fancy, a simple wrapper, which if malloc() returns NULL will print an error message to stderr and quit. Something like

   void* checked_malloc(size_t size) {
        void* ptr = malloc(size);
        if (ptr == NULL) {
            fprintf(stderr, "Failed to allocate %zd bytes\n", size);
            exit(1);
        }
        return ptr;
   }

One of the problems with this is fprintf - which might attempt to allocate memory on it's own and since we are out of memory already will ungracefully fail.

Is there any way to reliably log an error message after failed memory allocation? Or is there a better approach to write checked malloc()? A compiler agnostic solution is hugely preferred.

mpontillo · Accepted Answer · 2013-03-03 05:04:04Z

1

To be honest, I think you are being too paranoid. Your current solution looks fine. There is no reason fprintf() should fail with ENOMEM. It's just going to turn around and issue write() calls to the file descriptor for stderr (2). It has no reason to allocate any memory.

Of course, you could always try logging with direct write()s, like this:

static const char oom[] = "Out of memory!\n";
write(2, oom, sizeof(oom));

But again, that's probably overkill.

Also, you shouldn't worry about what every library call does regarding memory allocation. Using a checked malloc() is no substitute for good error checking elsewhere in your code.

edited Mar 3, 2013 at 5:04

answered Mar 2, 2013 at 2:23

mpontillo

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