Here is situation for my question:

main.c => is sourcecode for the program.
header.h => is header file that main.c include
|_ func1() exist in header.h but it is defined only for Prototype like this 'void func1(void);', which header.h doesn't define what func1() do,not at all.

lib/sumfunc.c => is the sourcecode for func1(), this time it define what func1() do.

-------------------

SO this is question, I want to know that how can 'main.c' use 'func1()' that defined only prototype in 'header.h' but its work is define in 'lib/sumfunc.c'.
How can we tell the compiler to know that?
I want to know the step to do that.

Thanks in advance.

in main.c and sumfunc.c you need to do

#define "header.h"

if the header files are in the build directory

or

#define <header.h>

if you have put it with the rest of your system header files.

Thanks slzckboy.