CODEWITHSUNDEEP
cpointers
George
George

Reputation: 7317

How does one use C pointer wrapper functions idiomatically?

From 21st-Century C:

The easiest way to avoid bugs related to malloc is not to use malloc.

and

Production code tends to have few uses of malloc, typically wrapped in new/copy/free functions so the main code doesn’t have to deal further with memory management.

Primary Question: Can someone provide a super simple, idiomatic example of how one might use function wrappers like this to subvert the direct usage of free and malloc?

Secondary Question (Optional): In particular, can the clever use of such functions emulate the behavior (or even some of the behavior) of the C++ shared_ptr and unique_ptr? That is, can using such functions free you from the worry that you might accidently free dangling pointers and/or create leaks? Or is that simply impossible in C, even with the use of such functions?

Upvotes: 1

Views: 377

Answers (2)

Steve Summit
Steve Summit

Reputation: 47923

Here are two popular idioms:

‌1. A wrapper around malloc so that it "never fails":

void safe_malloc(size_t size)
{
    char *ret = malloc(size);
    if(ret == NULL) {
        fprintf(stderr, "out of memory\n");
        exit(1);
    }
    return ret;
}

This way, you can call safe_malloc wherever you want, and never worry about checking its return value. But you can only use this idiom in a program where you don't mind the possibility that the program will spontaneously exit if malloc fails (i.e. if there's no data loss to be worried about in that case).

‌2. A "new" function for a particular structure type:

struct whatever *new_whatever()
{
    struct whatever *ret = safe_malloc(sizeof(*ret));
    initialize_whatever(ret);
    return ret;
}

I'm not sure these are what you're looking for, and I'm not sure they're what Ben Klemens is talking about. These don't really "solve" the memory allocation problem -- it can still be quite a nuisance -- but they help somewhat.

Upvotes: 1

user6307701
user6307701

Reputation:

Something like this? (It will add some compile time checking of the types, but that's about it)

typedef struct a_ {
   int a;
   int b;
} a;

a *new_a() {
     return malloc(sizeof(a));
}

void free_a(a *p) {
     free(p);
}

Secondary question: Smart pointers/safe memory management for C?

Upvotes: 2

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