CMake on UberMongoose

CMake Platform Specific Actions

Sun, 22 Dec 2013 10:13:40 +0530

Sometimes you need to link one library on Windows and another on Linux (or vice versa). CMake has a number of variables that allow you to do this easily:


UNIX	TRUE on all UNIX-like OS’s including Apple OS X and CygWin
WIN32	TRUE on Windows including CygWin
APPLE	TRUE on Apple systems. **
MINGW	TRUE when using the MinGW compiler in Windows
MSYS	TRUE when using the MSYS developer environment in Windows
CYGWIN	TRUE on Windows when using the CygWin version of cmake

** Note this does not imply the system is Mac OS X only that APPLE is #defined in C/C++ header files. Obtain more specific system information via CMAKE_SYSTEM_VERSION. I.e. IF(${CMAKE_SYSTEM_NAME} MATCHES “Darwin”) then it’s Mac OS X

CMake find_package

Wed, 04 Dec 2013 10:05:36 +0530

In the last scroll on CMake we discussed adding libraries that you write to your own code. This time, we look at using third party libraries out of the box. This turns out to be fairly easy with CMake - though there are exceptions (alternatively spelled “bugs”). Adding a third party package such as the precious Boost libraries for C++ is fairly easy with CMake. In your CMakeLists.txt file add a call to FIND_PACKAGE like so:

CMake add_library

Mon, 29 Jul 2013 09:57:52 +0530

In the last post we built an executable from a source file and a header only library. However, sometimes we need to build shared library binaries that can be linked into an executable. This is fairly simple with CMake. Instead of using add_executable like the last time we now simply need to use add_library like so:

# Sources 
file(GLOB Library_SOURCES *.cpp)
file(GLOB Library_HEADER *.hpp) 

# Executable
add_library(LibProject ${Library_SOURCES} ${Library_HEADERS})

CMake will now get the build system that you choose to create a shared library that can be linked into an executable one. You would end up with .lib files with Visual Studio and typically .a files with Unix make. Note that the name Library_SOURCES is chosen for clarities sake. The variable can be named anything.

CMake Include Directories

Sat, 20 Jul 2013 11:19:39 +0530

To do almost anything today with C++ requires the use of a number of different third party libraries. Some of these come in the form of header only libraries containing only include files (.h and .hpp). The references to these libraries are easy to resolve with CMake, let’s contrive an example.

Consider the following folder structure.

[CMakeHome] [CMakeHome]\src
Contains all the source code for the project

[CMakeHome]\headerlib\
Contains a small header only library with a number of different applications

CMake The Beautiful Beast

Wed, 17 Jul 2013 09:17:29 +0530

CMake is a mix of things. It’s a cross platform makefile generator that makes porting your C/C++ code from one OS to another or from one compiler to another inside the same OS really simple. However it complicates things a bit as well as now you need to write an extra “CMakeLists.txt” file for each of your code directories in order to allow CMake to generate those files for you. It doesn’t really help that the CMake documentation is rather dense and that there are a number of caveats that you really don’t see until you get to actually implementing it. Learning CMake therefore can be a harrowing experience and sometimes you might be tempted to give up half way and stick to the warm consolation of the Visual Studio IDE. That’s where this guide will hopefully help you as a starting point in your CMake journey that is not too steep to learn.

CMake Trickery - Platform Specific Linking

Wed, 26 Jun 2013 08:52:57 +0530

Quite often when your working on cross platform code you need to build applications that use one set of libraries when compiled under Microsoft Windows and another set when compiled under Unix/Linux. Fortunately CMake is a cunning tool to help you on your way. It has a bunch of predefined constants that you can use to switch libraries based on the platform like so:

# SomeCoolLibrary
IF (WIN32)
   message(STATUS "Building on Microsoft Windows.")
   set (SomeCoolLibrary someCoolWindows.lib)
ELSEIF (UNIX AND NOT MINGW)
   message(STATUS "Building on Linux/Unix.")
   set (SomeCoolLibrary someCoolLinux.so)
ENDIF()

Notice we check for the enviorenment being Unix but not MinGW. This is because CMake reports the enviorenment as Unix even if it’s MinGW running on Windows (which I suppose makes sense), but it pays to be specific. Finally you can target the generic link library that you’ve mentioned here: