C header issue: #include and “undefined reference”

Question

Alright, I\'ve been trying to work with this for the longest time, and I simply can\'t seem to get it to work right. I have three files, main.c, hello_world.c

Answer 1

gcc main.c hello_world.c -o main

Also, always use header guards:

#ifndef HELLO_WORLD_H
#define HELLO_WORLD_H

/* header file contents go here */

#endif /* HELLO_WORLD_H */

Answer 2

You should link object file compled from your second .c file hello_world.c with your main.o

try this

cc -c main.c
cc -c hello_world.c
cc *.o -o hello_world

Answer 3

You are not including hello_world.c in compilation.

   gcc hello_world.c main.c   -o main

Answer 4

Ya it seems you have forgotten to link hello_world.c. I will be gcc hello_world.c main.c -o main. If the number of files are less we can use this approach but in larger projects better to use Make files or some compilation scripts.

Answer 5

You are not linking against hello_world.c.

An easy way to do this is to run this compilation command:

cc -o main main.c hello_world.c

More complicated projects often use build scripts or make files that separate the compilation and linking commands, but the above command (combining both steps) should do fine for small projects.