Cmake Output/Build Directory

CMake how to set the build directory to be different than source directory

There's little need to set all the variables you're setting. CMake sets them to reasonable defaults. You should definitely not modify CMAKE_BINARY_DIR or CMAKE_CACHEFILE_DIR. Treat these as read-only.

First remove the existing problematic cache file from the src directory:

cd src
rm CMakeCache.txt
cd ..

Then remove all the set() commands and do:

cd Compile && rm -rf *
cmake ../src

As long as you're outside of the source directory when running CMake, it will not modify the source directory unless your CMakeList explicitly tells it to do so.

Once you have this working, you can look at where CMake puts things by default, and only if you're not satisfied with the default locations (such as the default value of EXECUTABLE_OUTPUT_PATH), modify only those you need. And try to express them relative to CMAKE_BINARY_DIR, CMAKE_CURRENT_BINARY_DIR, PROJECT_BINARY_DIR etc.

If you look at CMake documentation, you'll see variables partitioned into semantic sections. Except for very special circumstances, you should treat all those listed under "Variables that Provide Information" as read-only inside CMakeLists.

How to make cmake output to the build directory?

The usual way to do this, rather than changing variables to set the path, is simply to create the output directory, change to it, and run cmake from there. So instead of cmake . you usually have cmake .. or similar.

I understand the initial impulse to say "But I expect my build system to write output somewhere else." But CMake is not usually used in the way you were initially expecting, and other people who run your CMake build won't expect what you were expecting, so it's probably best to just use the built-in, default behavior, which is to put the output wherever cmake was run.

Put another way: You are fighting against the tool. Don't do that.

How do I make CMake output into a 'bin' dir?

As in Oleg's answer, I believe the correct variable to set is CMAKE_RUNTIME_OUTPUT_DIRECTORY. We use the following in our root CMakeLists.txt:

set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

You can also specify the output directories on a per-target basis:

set_target_properties( targets...
    PROPERTIES
    ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib"
    LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib"
    RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
)

In both cases you can append _[CONFIG] to the variable/property name to make the output directory apply to a specific configuration (the standard values for configuration are DEBUG, RELEASE, MINSIZEREL and RELWITHDEBINFO).

Specifying build directory within CMakeLists file

Afaik, with CMake the build directory is always the directory from where you invoke the cmake or ccmake command. So if you want to change the build directory, you have to change directories before running CMake.

To control the location where executables, static and shared libraries are placed once finished, you can modifiy CMAKE_RUNTIME_OUTPUT_DIRECTORY, CMAKE_ARCHIVE_OUTPUT_DIRECTORY, and CMAKE_LIBRARY_OUTPUT_DIRECTORY respectively.

CMake output directory by platform

One way would be to set the bin directories for the project:

math(EXPR platform_bits "${CMAKE_SIZEOF_VOID_P} * 8")
set(platform_dir ${CMAKE_SYSTEM_NAME}${platform_bits}-${CMAKE_CXX_COMPILER_ID}${CMAKE_CXX_COMPILER_VERSION})

foreach(config DEBUG RELEASE RELWITHDEBINFO MINSIZEREL)

    foreach(var CMAKE_ARCHIVE_OUTPUT_DIRECTORY_${config} CMAKE_LIBRARY_OUTPUT_DIRECTORY_${config} CMAKE_RUNTIME_OUTPUT_DIRECTORY_${config})
        set(${var} "${CMAKE_BINARY_DIR}/${platform_dir}-${config}")
        string(TOLOWER "${${var}}" ${var})
    endforeach()

endforeach()

This won't give you the exact directory names you are looking for, but is a good start. You can look at the CMake variables list for a list of platform specific configuration information. You would then need to apply some logic that will transform the CMake defined values into the specific ones you are looking for.

How to tell CMake where to put build files?

You can use the undocumented command line options -B and -H to specify your build directory and source directory respectively. So, from your project's root, you can do:

cmake -Bbuild -H.

(Where build is your build directory path.)

How best to set output directory for a CMake C++ project built by Visual Studio 2017?

I think the answer for my question is to modify buildRoot in CmakeSettings.json:

"buildRoot": "${workspaceRoot}\\build\\${name}"

Build system output folder structuring

You can do whatever you want with makefiles, but since you ask about cmake, the only way to do it is to run the build from the build folder. In other words, you do this (assuming that you have SolutionDir/CMakeLists.txt):

cd SolutionDir
mkdir Builds
cd Builds
cmake ..
make -j8

(or whatever make command that you want). The Builds directory can be anywhere you want, it doesn't have to be within SolutionDir. You pass the directory containing the CMakeLists.txt file to cmake.

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