Re: A interesting question about call C functions

[Greg Falcon <veloso@...>]

On Mon, Feb 28, 2011 at 11:07 AM, sagasw <sagasw@gmail.com> wrote:
> Hi all,
> I get this question from this chinese
> blog http://chenyufei.info/blog/2011-02-28/wrap-c-function-closure-gcc-nested-function/
> The author want to use closure in c language, and he found GCC has the
> ability of nested function (and closure).
> For example:
>
> typedef int (*func_t)(int arg);

> func_t create_wrap_function(func_t f) {
>
>     int wrapped(int arg) {
>
>         // call original function
>         int val = f(arg);
>
>         fprintf(log_func_call, "arg: %d ret: %d", arg, val);
>
>         return val;
>     }
>     return wrapped;
>
> }

You shouldn't do this, at least according to the GCC docs:

"If you try to call the nested function through its address after the
containing function has exited, all hell will break loose."

http://gcc.gnu.org/onlinedocs/gcc-4.5.2/gcc/Nested-Functions.html


Greg F