Compiling: undefined reference to

Question

I'm struggling with compiling multiple files into a common program. I'm getting an error:

undefined reference to 'pi'

Here's the skeleton of my code and Makefile. What am I doing wrong? Thanks!

File: calcPi.c

#include <stdlib.h>
#include <stdio.h>
#include <sched.h>
#include <string.h>

#include "pi.h"

int main(int argc, char* argv[]) {
    long iterations = 1000000;
    int policy = 2;
    int numChildren = 3;
    pi(iterations, policy, numChildren);
    return 0;
}

File: pi.h

void pi(long iterations, int policy, int numChildren);

File: pi.c

#include "pi.h"

void pi(long iterations, int policy, int numChildren) {
    //lots of code here
}

I'm compiling this using a Makefile:

CC = gcc
CFLAGS = -c -g -Wall -Wextra
LFLAGS = -g -Wall -Wextra

all: calcPi pi

calcPi: calcPi.o
    $(CC) $(LFLAGS) $^ -o $@ -lm

pi: pi.o
    $(CC) $(LFLAGS) $^ -o $@ -lm

calcPi.o: calcPi.c
    $(CC) $(CFLAGS) $<

pi.o: pi.c
    $(CC) $(CFLAGS) $<

clean:
    rm -f pi calcPi
    rm -f *.o
    rm -f *~

EDIT: In response to the request for the entire error message:

In function 'main'" calcPi.c:55: undefined reference to 'pi' collect2: error: ld returned 1 exit status make: * [calcPi.o] error 1

Please edit your question to include the complete console output from your build process (especially the line where things are being linked). — Oliver Charlesworth
– Oliver Charlesworth, Commented Mar 12, 2013 at 19:20
Your CFLAGS should not contain -c IIRC. and you probably want to link all your object files calcPi.o and pi.o together (unless you have two different main-s in them...) — Basile Starynkevitch
– Basile Starynkevitch, Commented Mar 12, 2013 at 19:20
@BasileStarynkevitch: I'd think -c would be appropriate if you want to separate the compilation and linking phases, which appears to be the case here. — cHao
– cHao, Commented Mar 12, 2013 at 19:24
Run make -p; it will shows you the default COMPILE.c and the rule using it — Basile Starynkevitch
– Basile Starynkevitch, Commented Mar 12, 2013 at 19:26

cHao · Accepted Answer · 2013-03-13 12:33:31Z

3

First of all, is pi really supposed to be a separate application?

You're referring the pi() function from calcPi, but it's only been compiled into pi.o, so you need to add it as a dependency.

What I think you want to do, is to create calcPi using the calcPi.o and pi.o object files.

CC = gcc
CFLAGS = -c -g -Wall -Wextra
LFLAGS = -g -Wall -Wextra

all: calcPi

calcPi: calcPi.o pi.o
    $(CC) $(LFLAGS) $^ -o $@ -lm

calcPi.o: calcPi.c
    $(CC) $(CFLAGS) $<

pi.o: pi.c
    $(CC) $(CFLAGS) $<

clean:
    rm -f calc
    rm -f *.o
    rm -f *~

edited Mar 13, 2013 at 12:33

cHao

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answered Mar 12, 2013 at 19:26

brain

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2 Comments

cHao Over a year ago

Might want to remove pi from all as well.

AndroidDev Over a year ago

That's it. Thanks! That helps me to understand this process a bit better.

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