Changing CMake files standard location

Question

I have a source directory with a folder called "phantom-dir/" where I put all generated files I don't need. I want to put all generated files by CMake inside this phantom directory (together with other generated and "ugly" files).

A mini example:

$ mkdir cmake-test $ cd cmake-test $ echo 'message("Hello World!")' > CMakeLists.txt $ cmake . | grep "Hello" Hello World! $ tree . ├── CMakeCache.txt ├── CMakeFiles │   ├── CMakeCCompiler.cmake │   ├── cmake.check_cache │   ├── CMakeCXXCompiler.cmake │   ├── CMakeDetermineCompilerABI_C.bin │   ├── CMakeDetermineCompilerABI_CXX.bin │   ├── CMakeDirectoryInformation.cmake │   ├── CMakeOutput.log │   ├── CMakeSystem.cmake │   ├── CMakeTmp │   ├── CompilerIdC │   │   ├── a.out │   │   └── CMakeCCompilerId.c │   ├── CompilerIdCXX │   │   ├── a.out │   │   └── CMakeCXXCompilerId.cpp │   ├── Makefile2 │   ├── Makefile.cmake │   ├── progress.marks │   └── TargetDirectories.txt ├── cmake_install.cmake ├── CMakeLists.txt └── Makefile  4 directories, 20 files 

By default, all CMake files (CMakeCache.txt, cmake_install.cmake, Makefile, CMakeFiles) are written in the working directory. But, I want something like that:

$ mkdir cmake-test $ cd cmake-test $ mkdir phantom-dir $ echo 'message("Hello World!")' > CMakeLists.txt $ // editing CMakeLists.txt to set some cmake variables. $ cmake . | grep "Hello" Hello World! $ tree . ├── phantom-dir │   ├── CMakeCache.txt │   ├── CMakeFiles │   │   ├── CMakeCCompiler.cmake │   │   ├── cmake.check_cache │   │   ├── CMakeCXXCompiler.cmake │   │   ├── CMakeDetermineCompilerABI_C.bin │   │   ├── CMakeDetermineCompilerABI_CXX.bin │   │   ├── CMakeDirectoryInformation.cmake │   │   ├── CMakeOutput.log │   │   ├── CMakeSystem.cmake │   │   ├── CMakeTmp │   │   ├── CompilerIdC │   │   │   ├── a.out │   │   │   └── CMakeCCompilerId.c │   │   ├── CompilerIdCXX │   │   │   ├── a.out │   │   │   └── CMakeCXXCompilerId.cpp │   │   ├── Makefile2 │   │   ├── Makefile.cmake │   │   ├── progress.marks │   │   └── TargetDirectories.txt │   ├── cmake_install.cmake ├── CMakeLists.txt └── Makefile  4 directories, 20 files 

That means: the Makefile in the current directory (to make, "cmake . && make"), but the remaining generated files inside the "phantom" directory.

I know I can make it with:

$ cd phantom-dir/ $ cmake ../ 

But it's a little tiresome for me to do it each time I want to re-compiling or remake cmake, above all taking into account that I'm modifying many times my CMakeLists.txt.

Which variables I have to set in the CMakeLists.txt file in order to achieve it?

Answer 1

You could make use of the undocumented CMake options -H and -B to avoid leaving your source dir. -H specifies the path to the main CMakeLists.txt file, and -B specifies the path to your desired build directory.

cmake -H. -Bphantom-dir 

Note that these are undocumented and so I suppose could change at any time the Kitware guys feel like.

To build your project without leaving your source dir, you can make use of the (official) option --build This is a cross-platform way to invoke your chosen build tool, and you can pass whatever flags you want to this tool. e.g.

cmake --build phantom-dir -- -j3