Thread: printf without include??

Originally Posted by quzah

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

asun, prepare to do A LOT of copying and pasting ;P lol

I could see people scrolling down the screen and saying themselves: "Where's the red!?" lol.

Code:

int printf(const char *format, ... );

int main(void)
{
   printf("a");
   return 0;
}

this code does work.
but i don't understand about

Code:

int printf(const char *format, ... );

what is this code do??
what does the format do??

thx dave_sinkula

Approximately? As far as printf() is concerned, isnt that all it would do?

Originally Posted by asun

Code:

int printf(const char *format, ... );

what is this code do??
what does the format do??

thx dave_sinkula

>What does this code do?
It's called a prototype function. It lets int main know there is a function called int printf(const char *) somewhere. If you put the full printf function on top of the int main, then you don't need a prototype function. You could do this:

Code:

#include <stdlib.h>
#include <stdio.h>

void bird(void) {
	puts("*whistle sound*");
}

int main(void) {
	bird();
	return 0;
}

OR

Code:

#include <stdlib.h>
#include <stdio.h>

void bird(void);

int main(void) {
	bird();
	return 0;
}

void bird(void) {
	puts("*whistle sound*");
}

But you CAN'T do this

Code:

#include <stdlib.h>
#include <stdio.h>

int main(void) {
	bird();
	return 0;
}

void bird(void) {
	puts("*whistle sound*");
}

Because you get this on compiling:

Code:

kleid@Shiva:~/Programming/Laboratory$ gcc prototype.c
prototype.c:9: warning: type mismatch with previous implicit declaration
prototype.c:5: warning: previous implicit declaration of `bird'
prototype.c:9: warning: `bird' was previously implicitly declared to return `int'

Because int main does not know where the void bird(void) function is.
>What does the format do?
The const char *format says that the function printf() has an argument that's a char array that won't be changed (hence the const). format is a string filled with %i's %d's %g's %f's %s's. The %whatever is a way of formatting your string output. That's why the char array is named format. You could even like this:

Code:

int printf(const char *JDFLkjserjsdflJER, ... );

There's my 2 cents.