I want to bundle five static libraries into one library in CMake. How can I proceed for this?
Like library a, b, c, d, and e should bundle into alpha_lib.
If you are using Visual Studio, you can take advantage of the Microsoft Library Manager (LIB.exe) to combine your static libraries into one. Your CMake could follow these steps:
Use find_program() to have CMake locate the MSVC lib.exe tool on your system. If you run cmake from the Visual Studio Command Prompt, find_program can locate lib.exe automatically, without using the optional PATHS argument to tell it where to look.
Use CMake's add_custom_target() command to call lib.exe using the syntax for merging libraries:
lib.exe /OUT:alpha_lib.lib a.lib b.lib c.lib d.lib e.lib
You can use target-dependent generator expressions in the custom target command to have CMake resolve the locations of your built libraries. The custom target will create a Project in your Visual Studio solution that can be run separately to merge all of the built static libraries into one library.
Your CMake could look something like this:
# Create the static libraries (a, b, c, d, and e)
add_library(a STATIC ${a_SOURCES})
...
add_library(e STATIC ${e_SOURCES})
# Tell CMake to locate the lib.exe tool.
find_program(MSVC_LIB_TOOL lib.exe)
# If the tool was found, create the custom target.
if(MSVC_LIB_TOOL)
add_custom_target(CombineStaticLibraries
COMMAND ${MSVC_LIB_TOOL} /OUT:$<TARGET_FILE_DIR:a>/alpha_lib.lib
$<TARGET_FILE:a>
$<TARGET_FILE:b>
$<TARGET_FILE:c>
$<TARGET_FILE:d>
$<TARGET_FILE:e>
WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
)
endif()
Visual Studio 2017 comes with full CMake integration. To learn about this combination, I was starting with this basic sample:
# CMakeLists.txt
cmake_minimum_required(VERSION 3.8)
project(foo)
add_executable(foo foo.cpp)
and
// foo.cpp
int main() {}
This properly generates build scripts, and compiles and links with no issues. That was easy.
Trying to set compiler options, on the other hand, turned out to be anything but trivial. In my case I was attempting to set the warning level to 4.
The obvious solution
add_compile_options("/W4")
didn't pan out as expected. The command line passed to the compiler now contains both /W4 (as intended) as well as /W3 (picked up from somewhere else), producing the following warning:
cl : Command line warning D9025: overriding '/W3' with '/W4'
To work around this, I would need to replace any incompatible compiler option(s) instead of just adding one. CMake does not provide any immediate support for this, and the standard solution (as this Q&A suggests) seems to be:
if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
else()
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /W4")
endif()
This, however, has two issues:
It sets the global CMAKE_CXX_FLAGS, applying to all C++ targets. This may not be intended (not an issue for me right now).
It doesn't scale. For every compiler option to add, you would have to read up on incompatible options, and manually strip those first. This will inevitably fail1.
My question is two-fold:
Where does the CMake integration pick up default settings from, and can this be controlled?
How do you set compiler options in general? (If this is too broad a topic, I'd be happy for help on setting the warning level only.)
1 Incidentally, the solution I replicated fails to account for the /Wall option, that is incompatible with /W4 as well.
The default settings for the compiler are picked up from standard module files located in the Modules directory of the CMake installation. The actual module file used depends on both the platform and the compiler. E.g., for Visual Studio 2017, CMake will load the default settings from the file Windows-MSVC.cmake and language specific settings from Windows-MSVC-C.cmake or Windows-MSVC-CXX.cmake.
To inspect the default settings, create a file CompilerOptions.cmake in the project directory with the following contents:
# log all *_INIT variables
get_cmake_property(_varNames VARIABLES)
list (REMOVE_DUPLICATES _varNames)
list (SORT _varNames)
foreach (_varName ${_varNames})
if (_varName MATCHES "_INIT$")
message(STATUS "${_varName}=${${_varName}}")
endif()
endforeach()
Then initialize the CMAKE_USER_MAKE_RULES_OVERRIDE variable in your CMakeLists.txt:
# CMakeLists.txt
cmake_minimum_required(VERSION 3.8)
set (CMAKE_USER_MAKE_RULES_OVERRIDE "${CMAKE_CURRENT_LIST_DIR}/CompilerOptions.cmake")
project(foo)
add_executable(foo foo.cpp)
When the project is configured upon opening the directory using Open Folder in Visual Studio 2017, the following information will be shown in the IDE's output window:
...
-- CMAKE_CXX_FLAGS_DEBUG_INIT= /MDd /Zi /Ob0 /Od /RTC1
-- CMAKE_CXX_FLAGS_INIT= /DWIN32 /D_WINDOWS /W3 /GR /EHsc
-- CMAKE_CXX_FLAGS_MINSIZEREL_INIT= /MD /O1 /Ob1 /DNDEBUG
-- CMAKE_CXX_FLAGS_RELEASE_INIT= /MD /O2 /Ob2 /DNDEBUG
-- CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT= /MD /Zi /O2 /Ob1 /DNDEBUG
...
So the warning setting /W3 is picked up from the CMake variable CMAKE_CXX_FLAGS_INIT which then applies to all CMake targets generated in the project.
To control the warning level on the CMake project or target level, one can alter the CMAKE_CXX_FLAGS_INIT variable in the CompilerOptions.cmake by adding the following lines to the file:
if (MSVC)
# remove default warning level from CMAKE_CXX_FLAGS_INIT
string (REGEX REPLACE "/W[0-4]" "" CMAKE_CXX_FLAGS_INIT "${CMAKE_CXX_FLAGS_INIT}")
endif()
The warning flags can then be controlled by setting the target compile options in CMakeLists.txt:
...
add_executable(foo foo.cpp)
target_compile_options(foo PRIVATE "/W4")
For most CMake projects it makes sense to control the default compiler options in a rules override file instead of manually tweaking variables like CMAKE_CXX_FLAGS.
When making changes to the CompilerOptions.cmake file, it is necessary to recreate the build folder. When using Visual Studio 2017 in Open Folder mode, choose the command Cache ... -> Delete Cache Folders from the CMake menu and then Cache ... -> Generate from the CMake menu to recreate the build folder.
Turning my comment into an answer
CMake does come with some compiler switches preset. For visual studio those are mainly standard link libraries, warning levels, optimization levels, exception handling, debug information and platform specific defines.
What you now have to differentiate when you want to change a CMake generated compiler settings are the following use cases:
Additional compiler flags CMake does not define vs. changing CMake's preset settings
Project default settings vs. project user defined settings
So let's discuss common solutions for those cases.
User changes/adds to Project/CMake Compiler Flags Defaults
The standard way would be to modify the cached compiler flags variables by using tools shipped with CMake like cmake-gui and ccmake.
To achieve this in Visual Studio you would have to:
CMake / Cache / View CMakeCache
Manually change e.g. CMAKE_CXX_FLAGS to /Wall
CMakeCache.txt
//Flags used by the compiler during all build types.
CMAKE_CXX_FLAGS:STRING= /DWIN32 /D_WINDOWS /Wall /GR /EHsc
CMake / Cache / Generate
Or you preset the CMAKE_CXX_FLAGS cache variable via a CMakeSettings.json file:
CMake / Change CMake Settings
Force the cache entry with -DCMAKE_CXX_FLAGS:STRING=... in cmakeCommandArgs
CMakeSettings.json
{
// See https://go.microsoft.com//fwlink//?linkid=834763 for more information about this file.
"configurations": [
{
"name": "x86-Debug (all warnings)",
"generator": "Visual Studio 15 2017",
"configurationType": "Debug",
"buildRoot": "${env.LOCALAPPDATA}\\CMakeBuild\\${workspaceHash}\\build\\${name}",
"cmakeCommandArgs": "-DCMAKE_CXX_FLAGS:STRING=\"/DWIN32 /D_WINDOWS /Wall /GR /EHsc\"",
"buildCommandArgs": "-m -v:minimal"
}
]
}
If you deliver this CMakeSettings.json file with your CMake project it gets permanent
Project changes to CMake Compiler Flags Defaults
If you want to keep most of CMake's compiler flags in place, #sakra's answer is definitely the way to go.
For my VS projects I've put the CXX flag settings into a toolchain file coming with the project itself. Mainly to freeze those settings and don't have a dependency the CMake version used or any environment variables set.
Taking the example from above that would look like:
VS2017Toolchain.cmake
set(CMAKE_CXX_FLAGS "/DWIN32 /D_WINDOWS /Wall /GR /EHsc" CACHE INTERNAL "")
CMakeSettings.json
{
// See https://go.microsoft.com//fwlink//?linkid=834763 for more information about this file.
"configurations": [
{
"name": "x86-Debug (all warnings)",
"generator": "Visual Studio 15 2017",
"configurationType": "Debug",
"buildRoot": "${env.LOCALAPPDATA}\\CMakeBuild\\${workspaceHash}\\build\\${name}",
"cmakeCommandArgs": "-DCMAKE_TOOLCHAIN_FILE:FILEPATH=\"${projectDir}\\VS2017Toolchain.cmake\"",
"buildCommandArgs": "-m -v:minimal"
}
]
}
References
Visual C++ Team Blog: CMake support in Visual Studio – the Visual Studio 2017 RC update
set diagnostics:caret from CMakeLists.txt
Is Cmake set variable recursive?
Passing compiler options cmake
In CMake 3.15, CMake introduced a fix for this MSVC-specific warning:
cl : Command line warning D9025: overriding '/W3' with '/W4'
and the compiler warning flags (like /W3) are no longer automatically added. So by upgrading to CMake 3.15 or greater, this warning should no longer appear. From the docs:
When using MSVC-like compilers in CMake 3.14 and below, warning flags like /W3 are added to CMAKE_<LANG>_FLAGS by default. This is problematic for projects that want to choose a different warning level programmatically. In particular, it requires string editing of the CMAKE_<LANG>_FLAGS variables with knowledge of the CMake builtin defaults so they can be replaced.
CMake 3.15 and above prefer to leave out warning flags from the value of CMAKE_<LANG>_FLAGS by default.
Along with this fix, CMake introduced policy CMP0092, which allows you to switch back to the OLD behavior (adding the warning flags by default) if necessary.
I try to use MSVC and MSVC_VERSION in toolchain file -
cmake-toolchain-file.cmake
message (STATUS "Toolchain MSVC=${MSVC} MSVC_VERSION=${MSVC_VERSION}")
CMakeLists.txt
message (STATUS "Project MSVC=${MSVC} MSVC_VERSION=${MSVC_VERSION}")
Output is
> cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake/cmake-toolchain-file.cmake
-- Toolchain MSVC= MSVC_VERSION=
-- Project MSVC=1 MSVC_VERSION=1800
-- Bulding target for: windows-x86
-- Configuring done
-- Generating done
-- Build files have been written to: D:/test/build
Is it normal behavior that I get MSVC and MSVC_VERSION from toolchain file empty?
Is it normal behavior that I get MSVC and MSVC_VERSION from toolchain file empty?
Yes. Variables initialized after project command. This is where toolchain read also. Try to add some extra messages:
cmake_minimum_required(VERSION 3.0)
message(STATUS "Before project: MSVC(${MSVC})")
project(Foo)
message(STATUS "After project: MSVC(${MSVC})")
Result:
-- Before project: MSVC()
-- Toolchain MSVC()
-- Toolchain MSVC()
...
-- After project: MSVC(1)
-- Configuring done
-- Generating done
So I guess you have one hidden question in mind:
Is it confusing?
Yes, for the Visual Studio generators. Since usually you can set some critical stuff like path to compiler in toolchain it doesn't make sense to read compiler-related variables like CMAKE_CXX_COMPILER_ID before toolchain processed, i.e. before project command. But when you set generator to Visual Studio your compiler is always MSVC. This gives you a hint for the workaround. Just check CMAKE_GENERATOR variable in toolchain instead of MSVC_VERSION (though this will not work for NMake generator of course):
if("${CMAKE_GENERATOR}" STREQUAL "Visual Studio 12 2013")
message("Toolchain: MSVC 1800")
endif()
if("${CMAKE_GENERATOR}" STREQUAL "Visual Studio 9 2008")
message("Toolchain: MSVC 1500")
endif()
I am trying to generate some Boost 1.58 libraries that I need (chrono, regex and thread) for Visual Studio 2012 and link the libraries with CMake. I have real problems for CMake and Visual Studio to find or link the libs, depending on the configuration I set.
I am finally using the following configuration:
bjam.exe --link=static --threading multi --variant=debug stage
But this doesn't seem to generate static libs.
How should I generate the libs and search them with CMake in order for Visual Studio to link them properly?
I finally came up with the solution and I think it is detailed enough to become a generic answer.
Visual Studio searches for dynamic libraries so we need to compile Boost libraries as shared, multithreaded, debug and release, and runtime-link shared. In windows using bjam.exe all commands have the prefix "--" except link, so the right way to build the libraries is:
bjam.exe link=shared --threading=multi --variant=debug --variant=release --with-chrono --with-regex --with-thread stage
This will generate the libs and DLLs in the folder Boost/stage/lib, so we need to set an environment variable Boost_LIBRARY_DIR C:/Boost/stage/lib, for example.
There are more options that may come in hand:
runtime-link = shared/static
toolset= msvc-11.0
The libraries will have a name like this for release:
boost_chrono-vc110-mt-1_58.lib
boost_chrono-vc110-mt-1_58.dll
And for debug:
boost_chrono-vc110-mt-gd-1_58.lib
boost_chrono-vc110-mt-gd-1_58.dll
In order for CMake to link them properly we need to write the following in the CMakeLists.txt:
add_definitions( -DBOOST_ALL_DYN_LINK ) //If not VS will give linking errors of redefinitions
set(Boost_USE_STATIC_LIBS OFF )
set(Boost_USE_MULTITHREADED ON)
set(Boost_USE_STATIC_RUNTIME OFF)
find_package(Boost COMPONENTS thread chrono regex REQUIRED )
INCLUDE_DIRECTORIES(${Boost_INCLUDE_DIRS})
TARGET_LINK_LIBRARIES( ${PROJ_NAME} ${Boost_LIBRARIES} )
bjam.exe --link=static --threading multi --variant=debug stage
But this doesn't seem to generate static libs.
Building the special stage target places Boost library binaries in the stage\lib\ subdirectory of the Boost tree.
More about building Boost on Windows here
CMake:
SET (CMAKE_BUILD_TYPE Debug) # in order to link with boost debug libs you may need to set that to build your program in debug mode (or do that from command line)
FIND_PACKAGE (Boost 1.58 COMPONENTS "chrono" "regex" "thread" REQUIRED)
#ADD_DEFINITIONS(-DBOOST_ALL_DYN_LINK) # make sure you don't have this as it will try to link with boost .dll's
INCLUDE_DIRECTORIES(${Boost_INCLUDE_DIRS})
LINK_DIRECTORIES(${Boost_LIBRARY_DIRS})
TARGET_LINK_LIBRARIES(${EXE_OR_LIB_NAME} ${Boost_LIBRARIES})
when I try to compile my project in MSVC2008 with the linker flag (Configuration properties>>Linker>>Command line>> Additional options) set to :
"/STACK:10000000 /machine:x64 /openmp"
it warns me that the /openmp flag is unknown.
"LINK : warning LNK4044: unrecognized option '/openmp'; ignored"
I want to know that MSVC automatically links the openmp libs when I added the compiler flag (Configuration properties>>C/C++>>Command line>>Additional options)
" /Zm1000 /EHs /MP /openmp /fp:fast"
or I should do sth else for getting rid of the warning.
The /openmp switch should be applied to the compiler, not linker. You can switch it on in C/C++ -> Language -> Open MP Support. The compiler then automatically instructs the linker to include the corresponding libraries.