C Smart Pointers

What this is

This project is a tentative attempt to bring smart pointer constructs to the (GNU) C programming language.

unique_ptr, shared_ptr macros, and smart type attribute
Destructor support for cleanup
Custom variable metadata on allocation

Installing

Prerequisites

To compile the library, GCC 4.9+ is needed.
To compile any project with the library, Clang or GCC are needed.

Installation

Clone this repository
run ./autogen.sh && ./configure --prefix=$HOME/ && make && make install from the project root for a local install, or run ./autogen.sh && ./configure && make && sudo make install for a global install.

Examples

Simple unique_ptr: simple1.c:

#include <stdio.h>
#include <csptr/smart_ptr.h>

int main(void) {
    smart int *some_int = unique_ptr(int);
    *some_int = 1;

    printf("%p = %d\n", some_int, *some_int);

    // some_int is destroyed here
    return 0;
}

Shell session:

$ gcc -std=c99 -o simple1 simple1.c -lcsptr
$ valgrind ./simple1
==3407== Memcheck, a memory error detector
==3407== Copyright (C) 2002-2013, and GNU GPL\'d, by Julian Seward et al.
==3407== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==3407== Command: ./test1
==3407==
0x53db068 = 1
==3407==
==3407== HEAP SUMMARY:
==3407==     in use at exit: 0 bytes in 0 blocks
==3407==   total heap usage: 1 allocs, 1 frees, 48 bytes allocated
==3407==
==3407== All heap blocks were freed -- no leaks are possible
==3407==
==3407== For counts of detected and suppressed errors, rerun with: -v
==3407== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Simple unique_ptr with destructor:

#include <unistd.h>
#include <fcntl.h>
#include <csptr/smart_ptr.h>

struct log_file {
    int fd;
    // ...
};

void cleanup_log_file(void *ptr, void *meta) {
    (void) meta;
    close(((struct log_file *) ptr)->fd);
}

int main(void) {
    smart struct log_file *log = unique_ptr(struct log_file, cleanup_log_file);
    *log = (struct log_file) {
        .fd = open("/dev/null", O_WRONLY | O_APPEND)
    };

    write(log->fd, "Hello", 5);

    // cleanup_log_file is called, then log is freed
    return 0;
}

Allocating a smart array and printing its contents before destruction:

#include <stdio.h>
#include <csptr/smart_ptr.h>
#include <csptr/array.h>

void print_int(void *ptr, void *meta) {
    (void) meta;
    // ptr points to the current element
    // meta points to the array metadata (global to the array), if any.
    printf("%d\n", *(int*) ptr);
}

int main(void) {
    // Destructors for array types are run on every element of the
    // array before destruction.
    smart int *ints = unique_ptr(int[10], print_int);

    // Smart arrays are length-aware
    for (size_t i = 0; i < array_length(ints); ++i) {
        ints[i] = i;
    }

    // Not initializing the array before getting out of scope
    // is undefined behavior: beware !
    return 0;
}

More examples

Using a different memory allocator (although most will replace malloc/free):

#include <csptr/smart_ptr.h>

void *some_allocator(size_t);
void some_deallocator(void *);

int main(void) {
    smalloc_allocator = (s_allocator) {some_allocator, some_deallocator};
    // ...
    return 0;
}

Automatic cleanup on error cases:

#include <unistd.h>
#include <fcntl.h>
#include <csptr/smart_ptr.h>

struct log_file {
    int fd;
    // ...
};

static void close_log(void *ptr, void *meta) {
    (void) meta;
    struct log_file *log = ptr;
    if (log->fd != -1)
        close(log->fd);
}

struct log_file *open_log(const char *path) {
    smart struct log_file *log = shared_ptr(struct log_file, close_log);
    if (!log) // failure to allocate
        return NULL; // nothing happens, destructor is not called

    log->fd = open(path, O_WRONLY | O_APPEND | O_CREAT, 0644);
    if (log->fd == -1) // failure to open
        return NULL; // log gets destroyed, file descriptor is not closed since fd == -1.

    return sref(log); // a new reference on log is returned, it does not get destoyed
}

int main(void) {
    smart struct log_file *log = open_log("/dev/null");
    // ...
    return 0; // file descriptor is closed, log is freed
}

Destructor macro helper:

#include <csptr/smart_ptr.h>

typedef struct {
    // ...
} A;

typedef struct {
    // ...
} B;

typedef struct {
    A *a;
    int some_int;
    B *b;
} C;

DESTRUCTOR(destroy_c, static, a, b) {
    printf("some_int = %d at destruction.\n", ptr->some_int); // why not ?
}

int main(void) {
    smart C *c = unique_ptr(C, destroy_c);
    *c = (C) {
        .a = unique_ptr(A),
        .b = unique_ptr(B),
        .some_int = 42
    };
    return 0; // c->a, c->b, and c are freed
}

FAQ

Q. Why didn't you use C++ you moron ?
A. Because when I first started this, I was working on a C project. Also, because it's fun.

Q. Can I use this on a serious project ?
A. Yes, but the project has yet to fully mature, beware of bugs!

Q. How did you make this ?
A. Here's a link to my blog post on the matter.

switchkiller/c-smart-pointers