How to Set Compiler Flags in Cross-Platform CMake Projects?

Modern Ways to Set Compiler Flags in Cross-Platform CMake Projects

Using CMake Generators and Expressions

CMake provides several methods for setting compiler flags in a modern and flexible manner. One approach is to use CMake generators and expressions, such as:

<code class="cmake">string(
    APPEND _opts
    "$<IF:$<CXX_COMPILER_ID:MSVC>,"
        "/W4;$<$<CONFIG:RELEASE>:/O2>,"
        "-Wall;-Wextra;-Werror;"
            "$<$<CONFIG:RELEASE>:-O3>"
            "$<$<CXX_COMPILER_ID:Clang>:-stdlib=libc++>"
    ">"
)

add_compile_options("${_opts}")</code>

Using add_compile_options()

Another method is to use the add_compile_options() command, which allows you to add compiler flags in a more readable and consistent manner:

<code class="cmake">if(MSVC)
    add_compile_options("/W4" "$<$<CONFIG:RELEASE>:/O2>")
else()
    add_compile_options("-Wall" "-Wextra" "-Werror" "$<$<CONFIG:RELEASE>:-O3>")
    if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
        add_compile_options("-stdlib=libc++")
    else()
        # nothing special for gcc at the moment
    endif()
endif()</code>

Best Practices

When setting up cross-platform CMake projects, it is good practice to follow these guidelines:

• Use CMake generators and expressions or add_compile_options() to set compiler flags.
• Avoid manually modifying CMAKE_CXX_FLAGS and similar variables.
• Use target_compile_features() to specify C features your code depends on, as it provides better error handling than explicitly setting the C standard.
• Consider using a wrapper script or multi-configuration IDE to build multiple configurations with a single CMake configuration.

Multi-Target Build

To build multiple targets in the same directory, create separate build configurations for each compiler and configuration combination, such as:

• x86-Debug-Clang
• x86-Release-Clang
• x86-Debug-MSVC
• x86-Release-MSVC

Then, you can use make targets to build each configuration:

• make x86-Debug-Clang
• make x86-Release-Clang
• make x86-Debug-MSVC
• make x86-Release-MSVC

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