Cannot used functions defined in header file

Question

My source file starts with:

#include "foo.h"

I am able to use all of my global variables, types, and structs from my header file. In my header file i started with a couple of includes:

#include<file.h>

Then move on to global variables:

#define GLOBAL

Then structs:

#typedef struct boo;

Then types. Then i go to function declarations. I.E:

size_t foo(int*r, size_t nitems);

What am I doing wrong that i am getting linker errors>

The #define global is just a global varibale definition, I have written: #define Global 5 But i am getting a LNK2001 — Matt
– Matt, Commented Jul 15, 2011 at 15:29
Please distill your program to a minimal, complete sample the demonstrates the problem and post that here, along with whatever compiler and linker errors it produces. For information about how to do that, and why it is important, see sscce.org. — Robᵩ
– Robᵩ, Commented Jul 15, 2011 at 17:00
You are including the header files, so the objects compile. But you need to include libraries for the objects to link to for the system (<>) header files with a -l compiler switch. — UncleO
– UncleO, Commented Jul 16, 2011 at 4:26

Bruce Stephens · Accepted Answer · 2011-07-15 15:25:17Z

1

The problem's presumably in how you're linking.

answered Jul 15, 2011 at 15:25

Bruce Stephens

7,5111 gold badge19 silver badges7 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Nigel Harper · Accepted Answer · 2011-07-15 15:56:15Z

1

The header file provides the function declaration to your source code. As you've found that's enough to get your code to compile but not to get it to link.

To get it to link you have to provide the linker with a file containing the actual compiled function - the function declaration is effectively a promise to the compiler that you will do this.

Exactly how you do it depends on what tools you're using and what form the compiled function is in.

answered Jul 15, 2011 at 15:56

Nigel Harper

1,2509 silver badges13 bronze badges

Comments

pmg · Accepted Answer · 2011-07-15 16:02:36Z

0

#define for simple substitution identifiers works exactly like a copy/paste.

After you do

#define GLOBAL 5

the following code

int GLOBAL;
GLOBAL = 13;
putchar(GLOBAL);

gets transformed to

int 5;
5 = 13;
putchar(5);

which obviously does not compile.

answered Jul 15, 2011 at 16:02

pmg

109k14 gold badges132 silver badges203 bronze badges

Collectives™ on Stack Overflow

Cannot used functions defined in header file

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related