Question

The Background

I have the following source code

#include <libubuntuone-1.0/u1-music-store.h>
#include <libsyncdaemon-1.0/libsyncdaemon/libsyncdaemon.h>

static void
get_credentials (U1MusicStore *music_store,
                                 gchar **oauth_consumer_token,
                                 gchar **oauth_consumer_secret,
                                 gchar **oauth_token,
                                 gchar **oauth_token_secret)
{
    SyncdaemonCredentials *credentials;
    *oauth_consumer_token = *oauth_consumer_secret = *oauth_token = *oauth_token_secret = NULL;

    *oauth_consumer_token = g_strdup (syncdaemon_credentials_get_consumer_key (credentials));
    *oauth_consumer_secret = g_strdup (syncdaemon_credentials_get_consumer_secret (credentials));
    *oauth_token = g_strdup (syncdaemon_credentials_get_token (credentials));
    *oauth_consumer_secret = g_strdup (syncdaemon_credentials_get_token_secret (credentials));
}

int main() 
{
    return 0;
}

and I am compiling it with the following makefile

main: main.o
    g++ main.o -o main

main.o: main.cpp
    g++ -c main.cpp `pkg-config --cflags --libs gtk+-2.0`

I need to include the pkg-config option since the u1-music-store.h header tried to included gtk/gtk.h, but the compiler isn’t able to find it on it’s own.

libsyncdaemon.h is a meta-header whose only purpose is to include a larger list of headers, which can be seen below

#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-authentication.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-config-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-credentials.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-daemon.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-events-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-file-info.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-filesystem-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-folder-info.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-folders-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-publicfiles-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-share-info.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-status-info.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-status-interface.h>
#include <libsyncdaemon-1.0/libsyncdaemon/syncdaemon-transfer-info.h>

My problem

Whenever I try to compile my code, I get the following error:

main.o: In function `get_credentials(_U1MusicStore*, char**, char**, char**, char**)':
main.cpp:(.text+0x34): undefined reference to `syncdaemon_credentials_get_consumer_key'
main.cpp:(.text+0x3c): undefined reference to `g_strdup'
main.cpp:(.text+0x4e): undefined reference to `syncdaemon_credentials_get_consumer_secret'
main.cpp:(.text+0x56): undefined reference to `g_strdup'
main.cpp:(.text+0x68): undefined reference to `syncdaemon_credentials_get_token'
main.cpp:(.text+0x70): undefined reference to `g_strdup'
main.cpp:(.text+0x82): undefined reference to `syncdaemon_credentials_get_token_secret'
main.cpp:(.text+0x8a): undefined reference to `g_strdup'
collect2: ld returned 1 exit status
make: *** [main] Error

Using grep, I’ve tracked down the four syncdaemon_credentials_get_* functions to syncdaemon-credentials.h, which I would expect the compiler to be able to find since it’s listed in libsyncdaemon.h, but for some reason that’s not happening. I’m assuming it’s for the reason that u1-music-store.h was unable to find gtk/gtk.h that compelled me to use the pkg-config option in my makefile, but I’m having trouble understanding why this is even the case to begin with. If the file’s #included, I would expect it to be included by the compiler.

Using grep again I was able to track down g_strdup to a number of headers, but I also discovered that when I replaced by makefile with the single command

g++ main.cpp -o main `pkg-config --cflags --libs gtk+-2.0`

I can eliminate the g_strdup warning, and I’m just left with the function errors.

My question

There are two things I’m looking to know here:

1. What should my makefile look like in order to solve my specific problem
2. What is the general solution to my problem? I’m guessing it’s something to do with daisy-chaining #include directives together, and having to use pkg-config to fix that, but I’m not sure.

Answer 1

1. You need to link against libsyncdaemon.so. Get the appropriate arguments from pkg-config ... libsyncdaemon-1.0.

2. You need to link against libraries that export the required symbols. If there is a .pc file then you can use it to get the appropriate arguments.