How to prevent multiple definitions in C?

Question

I\'m a C newbie and I was just trying to write a console application with Code::Blocks. Here\'s the (simplified) code: main.c:

#include 
#incl         


        

Answer 1

Including the implementation file (test.c) causes it to be prepended to your main.c and complied there and then again separately. So, the function test has two definitions -- one in the object code of main.c and once in that of test.c, which gives you a ODR violation. You need to create a header file containing the declaration of test and include it in main.c:

/* test.h */
#ifndef TEST_H
#define TEST_H
void test(); /* declaration */
#endif /* TEST_H */