How to properly compile and link a gdbus program

Question

I am trying to learn dbus and compilation/linking of programs on Linux. I am fairly new to building and linking applications from scratch. To this end, I am creating a simple client+server applications on Ubuntu which communicate over gdbus. I am using gdbus-codegen tool to generate .c and .h files for the dbus interfaces. I have created a sample xml description file named dbus_interface.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE node PUBLIC
  "-//freedesktop//DTD D-Bus Object Introspection 1.0//EN"
  "http://standards.freedesktop.org/dbus/1.0/introspect.dtd">
<node> 
    <interface name="org.hello.world">
        <method name="get_magic_number">
            <arg type="i" name="magic_number" direction="out"/>
        </method>
   </interface>
</node>    

and I am generating the code using the following command:

gdbus-codegen --generate-c-code generated_code dbus_interface.xml

which generates the generated_code.c and generated_code.h files. I have included the generated_code.h header file inside my client application, which I am trying to compile with gcc using the following command:

    gcc -Wall -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include client.c generated_code.c -o client

However, I get the following error:

generated_code.c:17:12: fatal error: gio/gunixfdlist.h: No such file or directory
   17 | #  include <gio/gunixfdlist.h>
      |            ^~~~~~~~~~~~~~~~~~~
compilation terminated.

Why is this header file not present on my system? I have the gio directory in /usr/include/glib-2.0/gio, and it contains a bunch of header files - but not gunixfdlist.h.

As a side note:

1. I am not using pkg-config in the build command on purpose in order to better understand what pkg-config expands to during the compilation
2. I guess that I will have to provide the actual library locations to the linker as well to my build command, but I wanted to solve the issue of not resolving includes properly first

Answer 1

The header file is in /usr/include/gio-unix-2.0/gio. As noted in the documentation:

Note that <gio/gunixfdlist.h> belongs to the UNIX-specific GIO interfaces, thus you have to use the gio-unix-2.0.pc pkg-config file when using it.

So you should be using pkg-config in your project configuration, and make sure that gio-unix-2.0 is included in the invocation that gets your compile flags.