Duplicate Symbol Error from C functions in Objective-C

Question

First off, I have only really used Objective-c methods in my programming. I decided to do a couple of quick math calculations as c functions and then ended up needing them for multiple classes. So then I stuck the c functions in a separate .h file. This works fine until I try and import the .h file into more than one class. Then I get this error:

Duplicate Symbol *_myFunction* blah blah blah Linker command failed with exit code 1 (use -v to see invocation)

How can I use a c function in more than one class without this link error. I've tried just defining the functions in the classes I need them in, but it seems that even if they are different classes, I get this error if the function name is the same. I'm probably crazy here, but some help understanding would be great.

Answer 1

You should put declarations in the .h file, make them extern, and move definitions into a .c or .m file.

From this

myfunctions.h

int max(int a, int b) {
    return a>b ? a : b;
}

Move to this:

myfunctions.h

extern int max(int a, int b); // declaration

myfunctions.c

int max(int a, int b) {
    return a>b ? a : b;
}