Comment by dllthomas

12 years ago

You need to free heap-allocated objects, but stack allocated objects are important and useful (particularly with RAII) and cleanly reversing such allocations eliminates a class of bugs.

4 comments

dllthomas

mike-cardwell 12 years ago

And of course, you don't even need to explicitly free heap-allocated objects if you're using C++11 smart pointers like shared_ptr and unique_ptr.

dllthomas 12 years ago

... mostly. Much like in a garbage collected language, you need to make sure you are no longer referencing things when you want resources to be freed, but it does make the worst case much harder to run into.

jlarocco 12 years ago

Stack allocated objects are cleaned up automatically in C, too...

dllthomas 12 years ago

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...