What's the use of __cdecl in function arguments in C

Question

I am learning C language and while learning I found a line of code which is totally new and strange for me void PullDown(char **, int, void (__cdecl **)(void)); I know about 1st and 2nd parameter only . I want to know about 3rd parameter. what's is the use of two asterisk after __cdecl ? I am aware from this syntax (type_cast *) so it is related to type casting ?

Answer 1

The 3rd parameter is pointer to function pointer. With only one asterix, it would be function pointer.

__cdecl is a compiler specific attribute that indicates that C calling convention must be used. See this page. If you play only with C or with other compiler, then you may ignore it.

Maybe example is helpful:

#include <stdio.h>

void PullDown(char **, int, void (**)(void));

int main(int argc, char **argv)
{
    void (*fun)(void);
    PullDown(NULL, 0, &fun);
    fun();
    return 0;
}

void my_function(void)
{
    printf("Hello!\n");
}

void PullDown(char **param1, int param2, void (**param3)(void))
{
    *param3 = my_function;    
}

It prints "Hello!"

In the example, fun is a function pointer variable. Pointer of fun is passed to the PullDown() function call. So PullDown() can set pointer of my_function() to the fun.