Thread: Functions, stack

Hi,

I have the following code:

Code:

#include <stdio.h>

char * returnString () {
	
	char *string;
	
	string = "Blah";
	
	return (string);
		
}

int main() {
	
	printf("%s\n", returnString());	
	
	return (0);	
}

First question: Is the string "Blah" stored on stack? If so, how come it can be printed in main()? Shouldn't it be removed off the stack right upon exiting function returnString()?

Second question: After compiling this code, my compiler gives me the following warning:

Call to function 'returnString' with no prototype in function main

Could you tell me why?


Thanks a lot, guys.

Originally Posted by Deckard

"Blah" is in the text segment, and the variable string is on the stack. For what it's worth, data on the stack is not erased when the stack pointer is moved to reclaim the space allocated during the call.

So the string (the actual text) is not stored on the stack? Sorry, I'm just trying to understand this.

Originally Posted by itsme86

Regarding the "no prototype" warning message, are you compiling your C code as C++? Which compiler are you using?

I'm using Borland's free C/C++ compiler. The file's extension is .c if that means anything, I'm new to this compiler so I don't know if that's enough information for it to compile as C, not C++.

I wrote a few programs where the function definition was before where it was being called, and it compiled without any warnings. This is the first time I got this warning.


Thanks for your replies.

To add to itsme86's answer, it is the C standard which requires that a string literal will be valid for the lifetime of a program.

http://dev.unicals.com/papers/c89-draft.html#3.1.4

A character string literal has static storage duration and type ``array of char ,'' and is initialized with the given characters.

http://dev.unicals.com/papers/c89-draft.html#3.1.2.4

An object declared with external or internal linkage, or with the storage-class specifier static has static storage duration. For such an object, storage is reserved and its stored value is initialized only once, prior to program startup. The object exists and retains its last-stored value throughout the execution of the entire program.

Second question: After compiling this code, my compiler gives me the following warning:

Call to function 'returnString' with no prototype in function main

Could you tell me why?

Code:

char * returnString ()

In C, this is not a complete function definition.

Empty parameter lists

C distinguishes between a function declared with an empty parameter list and a function declared with a parameter list consisting of only void. The former is an unprototyped function taking an unspecified number of arguments, while the latter is a prototyped function taking no arguments.

To define a function that takes no arguments, you must use the keyword void:

Code:

char * returnString (void) {

int main(void) {

Originally Posted by anonytmouse

Code:

char * returnString ()

In C, this is not a complete function definition.

To define a function that takes no arguments, you must use the keyword void:

Code:

char * returnString (void) {

int main(void) {

Thanks for the tip, I get no warnings now.