c void prototype and function

[Grenage]

I'm dabbling with C, and am a little flustered over the use of a void function. Let's say I have a basic menu, and depending on which option is selected, a function is called:


#include <stdio.h>

void networkfail(void);

int main() {

int menuselection;

printf("\n\nYadda Yadda:\n\n");
printf("1) Option 1.\n");
printf("2) Option 2.\n");
printf("3)\n");
printf("4)\n");
printf("5) Quit.\n\n");
scanf("%d", &menuselection);

switch (menuselection) {
case 1:
networkfail();
break;
case 2:
break;
case 3:
break;
case 4:
break;
case 5:
break;
default:
printf("That wasn't an option.");
break;
}

void networkfail() {
printf("Shame.");
}
return 0;
}

The compilation error is:

undefined reference to `networkfail'

What I don't understand, is why. As far as I am aware, the prototype is valid, and no parameters are required for the function. If I include 'void' in the function call, I'm informed that I have supplied too many parameters.

[r-senior]

You are creating a nested function (a function inside a function), which is not standard C.

Did you have a reason for doing so? Or did you mean to do this:


#include <stdio.h>

void networkfail();

int main() {
int menuselection;

printf("\n\nYadda Yadda:\n\n");
printf("1) Option 1.\n");
printf("2) Option 2.\n");
printf("3)\n");
printf("4)\n");
printf("5) Quit.\n\n");
scanf("%d", &menuselection);

switch (menuselection) {
case 1:
networkfail();
break;
case 2:
break;
case 3:
break;
case 4:
break;
case 5:
break;
default:
printf("That wasn't an option.");
break;
}
networkfail();
return 0;
}

void networkfail() {
printf("Shame.");
}

[Grenage]

Oh God, I knew it would end up being a stupid mistake; thank you for the correction.

[trent.josephsen]

You are creating a nested function (a function inside a function), which is not standard C.

Your analysis is correct, but I'm puzzled by the fact that you removed "void" from the parentheses of the function declaration, making it not a function prototype and preventing the compiler from catching the error if the function is later mistakenly called with arguments. void networkfail(void); was better.

[r-senior]

No puzzle, just a mistake on my part. The declarations would be better with void.