If you build a library with conan and set compiler.cppstd setting to e.g. 20 and call conan install, the libraries are still built with the default standard for the given compiler.
The docs say:
The value of compiler.cppstd provided by the consumer is used by the build helpers:
- The CMake build helper will set the CONAN_CMAKE_CXX_STANDARD and CONAN_CMAKE_CXX_EXTENSIONS definitions that will be converted to the corresponding CMake variables to activate the standard automatically with the conan_basic_setup() macro.
So it looks like you need to call conan_basic_setup() to activate this setting. But how do I call it? By patching a library's CMakeLists.txt? I sure don't want to do that just to have the proper standard version used. I can see some recipes that manually set the CMake definition based on the setting, e.g.:
But this feels like a hack either. So what is the proper way to make sure libraries are built with the compiler.cppstd I specified?
Avoid patching, it's ugly and fragile, for each new release you will need an update due upstream's changes.
The main approach is a CMakeLists.txt as wrapper, as real example: https://github.com/conan-io/conan-center-index/blob/5f77986125ee05c4833b0946589b03b751bf634a/recipes/proposal/all/CMakeLists.txt and there many others.
cmake_minimum_required(VERSION 3.1)
project(cmake_wrapper)
include(conanbuildinfo.cmake)
conan_basic_setup(KEEP_RPATHS)
add_subdirectory(source_subfolder)
The important thing here is including conanbuildinfo.cmake which is generated by cmake Conan generator, then the CMake helper will do the rest.
The source_subfolder here is project source folder, then the main CMakeLists.txt will be loaded after configuring all Conan settings.