RAII. [1]

Stack allocated objects have their memory freed in C. Other resources are not released.

Consider the following C, with and without gcc extensions:

    #include <stdio.h>
    #include <stdlib.h>
    #include <malloc.h>
    #include <fcntl.h>
    #include <unistd.h>

    #ifndef GCC_EXTENSIONS
    #define GCC_EXTENSIONS 1
    #endif

    int main() {
        {
            #if GCC_EXTENSIONS
            void close_fd(int *fdp) {
                if(*fdp >= 0) close(*fdp);
            }
            #else
            #define __attribute__(...)
            #endif
    
            int fd __attribute__((cleanup(close_fd))) = -1;
    
            fd = open("somefile", O_CREAT | O_WRONLY, 0644);
    
            system("ls /proc/self/fd");
        }
    
        system("ls /proc/self/fd");
    }

with gcc extensions:

    0 1 2 3 4
    0 1 2 3

without gcc extensions:

    0 1 2 3 4
    0 1 2 3 4

[1] http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initial...