How do I change order of Libs in a cmake file?

Link order matters. I have observed that when I compile my program with:

gcc `pkg-config --cflags --libs gtk+-2.0` program.cpp -o program

which produces a number of linker errors: "undefined reference to `_gtk_init_abi_check' ", and others. This can be remedied by specificying the input file before the libraries.

gcc program.cpp `pkg-config --cflags --libs gtk+-2.0` -o program

My Question:

How can I fix a problem of this nature when I am using a Cmake file? Here are the contents of a simple cmake file I am currently using.

cmake_minimum_required(VERSION 2.6)

project(program)

add_executable(program
program.cpp
)

EXEC_PROGRAM(pkg-config ARGS --cflags --libs gtk+-2.0 
             OUTPUT_VARIABLE GTK2_PKG_FLAGS)
SET(GTK2_PKG_FLAGS CACHE STRING "GTK2 Flags" "${GTK2_PKG_FLAGS}")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${GTK2_PKG_FLAGS}")

Now when I do a cmake followed by a make I get the same linker errors that the first line above gives me, so I know my linker problems are strictly related to order. So how do I change the link order when using pkg-config in a cmake file? I've tried reordering parts of my cmake file, but I don't seem to be finding the right order.

Solution

You have passed both the arguments --cflags and --libs in the command which will give both -I and -L parts of the .pc file in one variable.

Try running message("${GTK2_PKG_FLAGS}") to print the contents.

Hence it may not be prudent to link the complete variable $GTK2_PKG_FLAGS using target_link_libraries().

You may also want to try below steps

    INCLUDE(FindPkgConfig)
    pkg_check_modules(GTK REQUIRED gtk+-2.0)  

#include  
    include_directories(${GTK_INCLUDE_DIRS})  

#link  
    link_directories(${GTK_LIBRARY_DIRS})  
    target_link_libraries(program ${GTK_LIBRARIES})

Refer question