Changing CMake files standard location - build

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