cmake_multi generator

cmake_multi generator is intended for CMake multi-configuration environments, like Visual Studio and Xcode IDEs that do not configure for a specific build_type, like Debug or Release, but rather can be used for both and switch among Debug and Release configurations with a combo box or similar control. The project configuration for cmake is different, in multi-configuration environments, the flow would be:

$ cmake .. -G "Visual Studio 14 Win64"
# Now open the IDE (.sln file) or
$ cmake --build . --config Release

While in single-configuration environments (Unix Makefiles, etc):

$ cmake .. -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
# Build from your IDE, launching make, or
$ cmake --build .

The CMAKE_BUILD_TYPE default, if not specified is Debug.

With the regular conan cmake generator, only 1 configuration at a time can be managed. Then, it is a universal, homogeneous solution for all environments. This is the recommended way, using the regular cmake generator, and just go to the command line and switch among configurations:

$ conan install . -s build_type=Release ...
# Work in release, then, to switch to Debug dependencies
$ conan install . -s build_type=Debug ...

However, end consumers with heavy usage of the IDE, might want a multi-configuration build. The cmake_multi experimental generator is able to do that. First, both Debug and Release dependencies have to be installed:

$ conan install . -g cmake_multi -s build_type=Release ...
$ conan install . -g cmake_multi -s build_type=Debug  ...

These commands will generate 3 files: conanbuildinfo_release.cmake, conanbuildinfo_debug.cmake, and conanbuildinfo_multi.cmake, which includes the other two, and enables its use.

Warning

The cmake_multi generator is designed as a helper for consumers, but not for creating packages. If you also want to create a package, see Creating packages section.

Global variables approach

The consumer project might write a CMakeLists.txt like:

project(MyHello)
cmake_minimum_required(VERSION 2.8.12)

include(${CMAKE_BINARY_DIR}/conanbuildinfo_multi.cmake)
conan_basic_setup()

add_executable(say_hello main.cpp)
foreach(_LIB ${CONAN_LIBS_RELEASE})
    target_link_libraries(say_hello optimized ${_LIB})
endforeach()
foreach(_LIB ${CONAN_LIBS_DEBUG})
    target_link_libraries(say_hello debug ${_LIB})
endforeach()

Targets approach

Or, if using the modern cmake syntax with targets (where Hello1 is an example package name that the executable say_hello depends on):

project(MyHello)
cmake_minimum_required(VERSION 2.8.12)

include(${CMAKE_BINARY_DIR}/conanbuildinfo_multi.cmake)
conan_basic_setup(TARGETS)

add_executable(say_hello main.cpp)
target_link_libraries(say_hello CONAN_PKG::Hello1)

There’s also a convenient macro for linking to all libraries:

project(MyHello)
cmake_minimum_required(VERSION 2.8.12)

include(${CMAKE_BINARY_DIR}/conanbuildinfo_multi.cmake)
conan_basic_setup()

add_executable(say_hello main.cpp)
conan_target_link_libraries(say_hello)

With this approach, the end user can open the generated IDE project and switch among both configurations, building the project, or from the command line:

$ cmake --build . --config Release
# And without having to conan install again, or do anything else
$ cmake --build . --config Debug

Creating packages

The cmake_multi generator is just for consumption. It cannot be used to create packages. If you want to be able to both use the cmake_multi generator to install dependencies and build your project but also to create packages from that code, you need to specify the regular cmake generator for package creation, and prepare the CMakeLists.txt accordingly, something like:

project(MyHello)
cmake_minimum_required(VERSION 2.8.12)

if(EXISTS ${CMAKE_BINARY_DIR}/conanbuildinfo_multi.cmake)
    include(${CMAKE_BINARY_DIR}/conanbuildinfo_multi.cmake)
else()
    include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
endif()

conan_basic_setup()

add_executable(say_hello main.cpp)
conan_target_link_libraries(say_hello)

Then, make sure that the generator cmake_multi is not specified in the conanfiles, but the users specify it in the command line while installing dependencies:

$ conan install . -g cmake_multi

See also

Check the section Reference/Generators/cmake to read more about this generator.