Adding compiler flags to CMakeLists.txt
Solution 1
CMake has native support for all the things you're trying to solve by explicit flag specification, so you should use that instead:
cmake_minimum_required (VERSION 3.0)
project (foo)
add_executable (first first.cpp)
target_compile_options (first PRIVATE -std=c++11)
target_compile_definitions (first PRIVATE BOOST_ERROR_CODE_HEADER_ONLY)
target_link_libraries (first pthread)
If you can increase your minimum CMake version requirement to 3.1, you can replace the hard-coded std
flag with native CMake too:
cmake_minimum_required (VERSION 3.1)
project (foo)
add_executable (first first.cpp)
set_target_properties (first PROPERTIES
CXX_STANDARD 11
CXX_STANDARD_REQUIRED TRUE
CXX_EXTENSIONS FALSE
)
target_compile_definitions (first PRIVATE BOOST_ERROR_CODE_HEADER_ONLY)
target_link_libraries (first pthread)
The advatange is that not all compilers express "use C++11 without extensions" the same way, and CMake will translate the requirement to the correct flags for you.
If you're going to need the same C++11 setup for many executables, you can instead set CMake variables which prepopulate the properties. Note that the variables must be set before the executables are created:
set (CMAKE_CXX_STANDARD 11)
set (CMAKE_CXX_STANDARD_REQUIRED TRUE)
set (CMAKE_CXX_EXTENSIONS FALSE)
add_executable (first first.cpp)
target_compile_definitions (first PRIVATE BOOST_ERROR_CODE_HEADER_ONLY)
target_link_libraries (first pthread)
add_executable (second second.cpp)
target_compile_definitions (second PRIVATE BOOST_ERROR_CODE_HEADER_ONLY)
target_link_libraries (second pthread)
# ... and so on
Solution 2
In general, one should specify libraries using target_link_libraries
instead of overriding linker flags directly.
In this case, you can do it differently:
add_executable (first first.cpp)
find_package(Threads REQUIRED)
target_link_libraries(first PRIVATE Threads::Threads)
Threads::Threads
above stands for threading library for your system. This has the advantage of being cross platform - when you want to compile your project on, e. g. Windows, linker won't complain about unknown pthread
library.
For the same reason, setting C++ version the way @Angew does in theirs answer is preferred - it just works, without having to manually adjust flags for each compiler.
user6646922
Updated on June 04, 2022Comments
-
user6646922 over 1 year
I want to use the newest version of Boost library and have the following contents of a
CMakeLists.txt
file:cmake_minimum_required (VERSION 3.0) project (foo) set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -DBOOST_ERROR_CODE_HEADER_ONLY -lpthread") # set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -lpthread") add_executable (first first.cpp)
With that I keep getting the following linker error:
undefined reference to `pthread_detach
However, if I compile my code without the use of CMake, with the following command:
g++ foo.cpp -std=c++11 -DBOOST_ERROR_CODE_HEADER_ONLY -lpthread
It works fine.
The question is how to get it to work using CMake. Why doesn't it work when I specify the compiler flags via setting
CMAKE_CXX_FLAGS
? I thought I might have to specifyCMAKE_EXE_LINKER_FLAGS
instead, but doing that doesn't help at all. -
joe_chip over 5 yearsAdditionally, starting with CMake 3.8, it's possible to do:
target_compile_features(first PUBLIC cxx_std_11)
to set C++ standard. This way targets that depend onfirst
will automagically be built with C++11 flags.