Unable to compile GTK+ application

Question

I'm trying to compile a simple GTK app for testing on a Trisquel 7 machine. The packages are derived from Ubuntu 14.04 LTS. I have libgtk2.0-dev installed, but when I try to compile, this is the result.

$ gcc -Wall -Wextra -std=c11 `pkg-config --libs --cflags gtk+-2.0` main.c
a_out-main.o: In function `main':
/home/mac/c/main.c:7: undefined reference to `gtk_init'
/home/mac/c/main.c:9: undefined reference to `gtk_window_new'
/home/mac/c/main.c:10: undefined reference to `gtk_window_get_type'
/home/mac/c/main.c:10: undefined reference to `g_type_check_instance_cast'
/home/mac/c/main.c:10: undefined reference to `gtk_window_set_title'
/home/mac/c/main.c:11: undefined reference to `g_type_check_instance_cast'
/home/mac/c/main.c:11: undefined reference to `gtk_window_set_default_size'
/home/mac/c/main.c:12: undefined reference to `g_type_check_instance_cast'
/home/mac/c/main.c:12: undefined reference to `gtk_window_set_position'
/home/mac/c/main.c:13: undefined reference to `gtk_widget_show'
/home/mac/c/main.c:15: undefined reference to `g_type_check_instance_cast'
/home/mac/c/main.c:15: undefined reference to `gtk_main_quit'
/home/mac/c/main.c:15: undefined reference to `g_signal_connect_data'
/home/mac/c/main.c:18: undefined reference to `gtk_main'

I have checked the output of pkg-config --libs --cflags gtk+-2.0, and it looks correct, but for some reason, it's not being correctly linked.

Answer 1

Put the backticks containing the pkg-config command at the end of the line. For some reason, gcc only reads it correctly if it's last. I had the exact same problem today trying to build examples from the GTK repo. The line in their makefiles,

$(CC) -o $(@F) $(LIBS) $(OBJS)

ought to be

$(CC) -o $(@F) $(OBJS) $(LIBS)

instead.

Answer 2

I believe the problem is that the linker is single-pass. I.e., it must see a reference before it finds its definition. Thus, the pkg-config bit, where the definitions are pointed out, must come after main.c, where the references are.