Add a function globally to use throughout an iPhone App

I want to add a simple function to a central place so that I ca开发者_开发百科n use it without having to include the header files over and over again. How do I accomplish it?

Consider the function

void foo() {
    printf("Bar");
}

I tried adding this to a foo.h file and then including it in the prefix.pch file. But a compilation error occurs saying duplicate symbol.

You need to use inclusion guards, like this:

#ifndef FOO_H
#define FOO_H

void foo(); //declaration

#endif

And in Foo.m:

void foo() {
   printf("Bar");
}

Or, even easier, you can simply use the #import directive:

#import "Foo.h"

If you did all of the above, then the only way this could've happened is if you explicitly declared a new function with the same name inside another file

header (foo.h):

void foo();

implementation file (foo.m)

void foo() {
// blah
} 

Stick your foo.h in your PCH and away you go.

Include your function in a separate class.
And include the header of that class to all of your classes.