How to use pkg-config in Make

Question

I want to compile the simplest GTK program. I can compile it using the command line:

gcc $(pkg-config --cflags --libs gtk+-3.0)  main.c -o main.o

However, if I use Make it doesnt work:

CFLAGS=-g -Wall -Wextra $(pkg-config --cflags)
LDFLAGS=$(pkg-config --libs gtk+-3.0)
CC=gcc

SOURCES=$(wildcard *.c)
EXECUTABLES=$(patsubst %.c,%,$(SOURCES))

all: $(EXECUTABLES)

It tells me this:

gcc -g -Wall -Wextra    -c -o main.o main.c
main.c:1:21: fatal error: gtk/gtk.h: No such file or directory
 #include <gtk/gtk.h>
                     ^
compilation terminated.
<builtin>: recipe for target 'main.o' failed
make: *** [main.o] Error 1

Where do I stick $(pkg-config --cflags --libs gtk+-3.0) in the Makefile to make it compile?

Thanks very much in advance for your kind help.

Answered [here](http://stackoverflow.com/questions/20145132/makefiles-how-can-i-use-them/20146082#20146082) — Basile Starynkevitch, Feb 16 '15 at 01:04
Not quite; this does show a fix if you look hard enough. Keep this comment anyway. — andlabs, Feb 16 '15 at 01:55
More an alternative than an answer, but maybe you can consider using CMake instead of plain Makefiles. It has a much better syntax and is cross-platform. — SukkoPera, Feb 16 '15 at 09:27

score 53 · Answer 1 · answered Feb 16 '15 at 01:59

There are two issues.

First, your CFLAGS line is wrong: you forgot to say gtk+-3.0 in the pkg-config part, so pkg-config will spit out an error instead:

CFLAGS=-g -Wall -Wextra $(pkg-config --cflags gtk+-3.0)

Second, and more important, $(...) is intercepted by make itself for variable substitution. In fact, you've seen this already:

SOURCES=$(wildcard *.c)
EXECUTABLES=$(patsubst %.c,%,$(SOURCES))

all: $(EXECUTABLES)

is all done by make.

There are two things you can do.

First, you can use `...` instead, which does the same thing ($(...) is newer shell syntax).

CFLAGS=-g -Wall -Wextra `pkg-config --cflags gtk+-3.0`
LDFLAGS=`pkg-config --libs gtk+-3.0`

Second, since you seem to be using GNU make, you can use the shell substitution command, which was shown in the answer Basile Starynkevitch linked above:

CFLAGS=-g -Wall -Wextra $(shell pkg-config --cflags gtk+-3.0)
LDFLAGS=$(shell pkg-config --libs gtk+-3.0)

And make helpfully doesn't warn about undefined variables/functions :) Cost me an hour thinking I new how to write a simple makefile ^^ — olejorgenb, Jan 24 '17 at 00:26
Another way is to escape the `$` character: `$$(pkg-config --libs module)`. — nebel, Sep 22 '20 at 12:37

How to use pkg-config in Make

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