Thread: GCC Linking against static library

I'm looking at setting up a simple development environment for an embedded project.

I want to write unit tests as I code, so I have decided to go with two trees:

/proj/target (contains project code and test files)

/proj/hosted (contains makefiles that specify rules to build for host environment)


Now lets say I develop a library, in this case call it math:

/proj/target/lib/math/math.h

Code:

/* Add two numbers */
int addition(int x, int y);

/* Subtract two numbers */
int subtraction(int x, int y);

/proj/target/lib/math/math.c

Code:

#include "math.h"

int addition(int x, int y)
{
	return x + y;
}

int subtraction(int x, int y)
{
	return x - y;
}

And now I want to create a hosted build of this on the "hosted" tree, so I have a runner that will eventually run some unit tests:

/proj/hosted/lib/math/runner.c

Code:

#include <stdio.h>
#include <math.h>

int main(void)
{
	printf("addtion(3,6)=%d\n", addition(3,6));
	printf("subtraction(8,3)=%d\n", subtraction(8,3));
}

And then a makefile that I want to:

1. Compile the math source into a static library.
2. Compile the runner and link against the math library.

The makefile looks like this...

/proj/hosted/lib/math/makefile

Code:

LIB_BASE = /proj/target/lib/
LIB_NAME = math

MATH_SOURCES = $(abspath $(wildcard $(LIB_BASE)$(LIB_NAME)/*.c))

default:
	# Compile the library code, put the built library in current directory.
	gcc -c $(MATH_SOURCES) -o ${CURDIR}/$(LIB_NAME).o

	# Compile the runner, link against the math lib.
	gcc runner.c -I$(LIB_BASE)$(LIB_NAME) -L$(CURDIR) -lmath -o runner

Library math is compiled into the local directory, then runner is compiled linking against the math library, however, something is wrong at the linking stage; when running make it can't find the math library:

Code:

[user@localhost math]$ make
# Compile the library code, put the built library in current directory.
gcc -c /proj/target/lib/math/math.c -o /proj/hosted/lib/math/math.o
# Compile the runner, link against the math lib.
gcc runner.c -I/proj/target/lib/math -L/proj/hosted/lib/math -lmath -o runner
/usr/bin/ld: cannot find -lmath
collect2: error: ld returned 1 exit status
makefile:7: recipe for target 'default' failed
make: *** [default] Error 1

Any ideas what I'm doing wrong/missing?

Cas is right here. If you were making a shared library, you wouldn't have to use the ar command I believe. But because you're creating a static library, you need to use the ar command to create the library. The c option means create archive
The r option means to replace the files in the archive, ie, insert them, regardless of whether they're already in there or not. And the u option affects the r option in a way. I believe the u option updates the files, ie, it only adds them if they're newer than the ones that are already added into the archive.

I can't remember the reason, but I want to say I remember something about having to run ranlib too or something.