Question

I have been using a makefile that I inherited from the internet for long enough! It is time that I learn to compile my own projects once and for all. So I’ve read some tutorials and thrown together a mock-up. It doesn’t work, and I am at my wits end now (which is usually when I come to YOU).

As usual, thank you all in advance for being so knowledgeable.

lib.h

#ifndef LIB_H
#define LIB_H

/** returns the integer zero (0), because the 
 * 0 key on my keyboard is broken. 
 * @pre my keyboard is broken 
 * @post nope, still broken
 * @returns 0 */
int zero();

#endif

lib.cpp

#include "lib.h"

int zero() {

  return 0;
}

project.cpp

#include "lib.h"

int main () {

  int i = zero();

  return 0;
}

makefile
(the arrows are tab characters)

project: lib.o project.o
-->g++ lib.o project.o -o project

project.o: project.cpp lib.h
-->g++ -c project.cpp

lib.o: lib.cpp lib.h
-->g++ -c lib.cpp

When, from the command line, I run

$ make

I get the following error:

g++ project.cpp
/tmp/ccWCSqSx.o: In function 'main':
project.cpp:(.text+0x9): undefined reference to 'zero()'
collect2: ld returned 1 exit status
make: *** [project.o] Error 1

This is clearly a case of me having missed some crucial piece of information somewhere along the lines. I’ve googled this a bunch, but most of the results have been people with real problems, and I haven’t been able to learn what’s missing. Looking forward to being tremendously embarrassed by the answer,

Thanks!

Answer 1

The error message gives the command line:

g++ project.cpp

Note the lack of -c. That’s apparently not in your makefile, in spite of what you think.