Thread: Function pointer doubt

I was doing pointer to function program from example and made my version of the program.

Code:

#include<stdio.h>

int testfunction(int);

void testfunction1(void);

int (*comp)(int);

int passfunciton(int (*)(int));

int main(int argc, char *argv[])
{
 passfunction((int(*)(int))(testfunction1));
 passfunction(testfunction1);
 
 return 0;
}
int testfunction(int var)
{
    printf("%d",var);
}

int passfunction(int (*comp)(int))
{
    (*comp)(15);
}

void testfunction1(void)
{
    printf("%d\n",16);
}

The first passfunction is from example with some modifications. Does the

Code:

(int(*)(int)) is for type casting?

I removed that even then it compiles without warning. My main doubt is testfunction1 is of different type even then it compiles without warnings. Why?

If it compiles without errors or warnings for you it is because you have your compiler warning levels too low. Here are the warnings and errors I got when compiling your code:

main.c||In function ‘main’:|
main.c|13|error: implicit declaration of function ‘passfunction’ [-Wimplicit-function-declaration]|
main.c|11|warning: unused parameter ‘argc’ [-Wunused-parameter]|
main.c|11|warning: unused parameter ‘argv’ [-Wunused-parameter]|
main.c|23|warning: no previous declaration for ‘passfunction’ [-Wmissing-declarations]|
main.c||In function ‘passfunction’:|
main.c|23|warning: declaration of ‘comp’ shadows a global declaration [-Wshadow]|
main.c|7|warning: shadowed declaration is here [-Wshadow]|
main.c||In function ‘testfunction’:|
main.c|21|warning: control reaches end of non-void function [-Wreturn-type]|
main.c||In function ‘passfunction’:|
main.c|26|warning: control reaches end of non-void function [-Wreturn-type]|
||=== Build finished: 1 errors, 7 warnings (0 minutes, 0 seconds) ===|

Jim

Here's what I get via GCC:

Code:

main.c: In function 'main':
main.c:20:3: warning: implicit declaration of function 'passfunction' [-Wimplicit-function-declaration]
   passfunction((int(*)(int))(testfunction1));
   ^
main.c:18:14: warning: unused parameter 'argc' [-Wunused-parameter]
 int main(int argc, char *argv[])
              ^
main.c:18:26: warning: unused parameter 'argv' [-Wunused-parameter]
 int main(int argc, char *argv[])
                          ^
main.c: In function 'testfunction':
main.c:28:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
main.c: In function 'passfunction':
main.c:33:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

It barks about the return because I didn't compile with C99 or anything. This is what C89 would say about your code.