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RequireCXX17.cmake
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RequireCXX17.cmake
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# Detect if compiler version is sufficient for supporting C++17.
# If it is, CMAKE_CXX_FLAGS are modified appropriately and HAVE_CXX17
# is set to a true value. Else, CMake exits with a fatal error message.
# This currently only works for GCC and Clang compilers.
# In Cmake 3.8+, CMAKE_CXX_STANDARD_REQUIRED should be able to replace
# all the logic below.
if (DEFINED HAVE_CXX17)
return()
endif ()
set(required_gcc_version 8.0)
set(required_clang_version 9.0)
set(required_msvc_version 19.14)
set(required_apple_clang_version 11.4)
if (MSVC)
if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${required_msvc_version})
message(
FATAL_ERROR
"MSVC version must be at least "
"${required_gcc_version} for C++17 support, detected: "
"${CMAKE_CXX_COMPILER_VERSION}")
endif ()
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /std:c++17")
set(HAVE_CXX17 true)
return()
endif ()
include(CheckCXXSourceCompiles)
set(cxx17_testcode "#include <optional>
int main() { std::optional<int> a; }")
check_cxx_source_compiles("${cxx17_testcode}" cxx17_already_works)
if (cxx17_already_works)
# Nothing to do. Flags already select a suitable C++ version.
set(HAVE_CXX17 true)
return()
endif ()
set(cxx17_flag "-std=c++17")
if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${required_gcc_version})
message(
FATAL_ERROR
"GCC version must be at least "
"${required_gcc_version} for C++17 support, detected: "
"${CMAKE_CXX_COMPILER_VERSION}")
endif ()
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${required_clang_version})
message(
FATAL_ERROR
"Clang version must be at least "
"${required_clang_version} for C++17 support, detected: "
"${CMAKE_CXX_COMPILER_VERSION}")
endif ()
if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5)
set(cxx17_flag "-std=c++1z")
endif ()
elseif (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS ${required_apple_clang_version})
message(
FATAL_ERROR
"Apple Clang version must be at least "
"${required_apple_clang_version} for C++17 support, detected: "
"${CMAKE_CXX_COMPILER_VERSION}")
endif ()
else ()
# Unrecognized compiler: fine to be permissive of other compilers as long
# as they are able to support C++17 and can compile the test program, but
# we just won't be able to give specific advice on what compiler version a
# user needs in the case it actually doesn't support C++17.
endif ()
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${cxx17_flag}")
check_cxx_source_compiles("${cxx17_testcode}" cxx17_works)
if (NOT cxx17_works)
message(FATAL_ERROR "failed using C++17 for compilation")
endif ()
set(HAVE_CXX17 true)