Detecting C 11 Support in Compilers with CMake

One of the challenges in software development is ensuring compatibility with different compiler versions and their feature sets. In particular, determining whether a compiler supports C 11 can be crucial for projects relying on newer language features.

CMake provides a convenient way to address this issue. With CMake version 3.1.0 and later, it offers the CMAKE_CXX_COMPILE_FEATURES variable, which lists the C features supported by the active compiler.

In practice, instead of relying directly on this variable, CMake provides more structured mechanisms for specifying C language standards and features.

Specifying the C Standard Explicitly

One option is to set the CXX_STANDARD and CXX_STANDARD_REQUIRED properties for your CMake target. This explicitly specifies the desired C standard and whether it is mandatory (if the compiler does not support it, the build will fail).

For example:

add_executable(prog main.cc)
set_property(TARGET prog PROPERTY CXX_STANDARD 11)
set_property(TARGET prog PROPERTY CXX_STANDARD_REQUIRED ON)

Specifying Required C Features

Alternatively, you can use the target_compile_features command to specify the C features used by your target. CMake will then deduce the appropriate C standard from these features.

The CMAKE_CXX_KNOWN_FEATURES global property lists the available C features for consideration.

For example:

add_executable(foobar main.cc)
set(needed_features
    cxx_strong_enums
    cxx_constexpr
    cxx_auto_type)
target_compile_features(foobar PRIVATE ${needed_features})

Checking for Supported Features

To verify the supported C features of your compiler:

cmake_minimum_required(VERSION 3.1.0 FATAL_ERROR)
project(foobar CXX)
message("Your C   compiler supports these C   features:")
foreach(feature in ${CMAKE_CXX_COMPILE_FEATURES})
    message(feature)
endforeach()

These methods give you flexibility and control over the C language standard and features used in your CMake projects.