function in a function in C compiling with gcc

joel2001k · 06-22-2007, 02:12 PM

I would like to write in C compiling with gcc a function in a function and call it within it, it might look like

Code:

#include <stdio.h>

void
func_a(){
  int value;
  void func_b();

  value = 0;
  func_b();

  void func_b(){
    fprintf(stdout, "%d\n\0", value);
  }
}

int
main(int argc, char **argv){
  func_a();
}

I have tried it, but i got errors like

Code:

error: invalid storage class for function "func_b"
error: invalid storage class for function "func_b"
warning: conflicting types for "func_b"
error: static declaration of "func_b" follows non-static declaration
error: previous implicit declaration of "func_b" was here

card-suse · 06-22-2007, 02:53 PM

You can't do it. It violates the C standard. All function declarations are considered external, so you can't define a function within another function.

You would have to do something like:

Code:

#include <stdio.h>

void 
func_b(int value){
    fprintf(stdout, "%d\n\0", value);
}

void
func_a(){
  int value;

  value = 0;
  func_b(value);

}

int
main(int argc, char **argv){
  func_a();
}

nc3b · 06-23-2007, 02:47 AM

I agree to card-suse. But most people like to place the prototypes of their functions at the top and define the functions after main.

PHP Code:



#include <stdio.h>

void func_a(int);
void func_b(int);

int main(int argc, char **argv)
{
  func_a();
}

void func_a()
{
  int value;

  value = 0;
  func_b(value);
}

func_b(int value)
{
    fprintf(stdout, "%d\n\0", value);
}

(It doesn't matter in which way you declare and define the functions this way).

taylor_venable · 06-23-2007, 09:40 AM

Nested functions are supported in GCC: http://gcc.gnu.org/onlinedocs/gcc-4....sted-Functions

And so is lexical scoping, so what you're trying to do makes perfect sense.

As far as the "invalid storage class" errors go, I think your particular version of GCC may be too old. Which one are you using? (These errors do not appear in 4.1.2 which is what I used with your code.) Or perhaps some of the command-line arguments you pass to GCC inhibit the GNU extensions? (I compiled with no options.)

For the conflicting declarations, I got it to work by making the declaration and definition in the same line, and placing it before the call, like so:

Code:

void
func_a(){
  int value;
  void func_b(){
    fprintf(stdout, "%d\n\0", value);
  }

  value = 0;
  func_b();

}

And it works exactly as expected.

card-suse · 06-23-2007, 08:16 PM

Will that be portable? I was referencing Ritchie's book on C when I posted. Is this part of the ANSI standard? Thanks.

taylor_venable · 06-23-2007, 08:18 PM

Quote:

Originally Posted by card-suse

Will that be portable? I was referencing Ritchie's book on C when I posted. Is this part of the ANSI standard? Thanks.

Nope, it's a GNU extension. But the OP mentions GCC, so I said it.