[SOLVED] CMAKE_WARN_DEPRECATED does not disable deprecated warnings

Issue

I run cmake as follows:

cmake . -G Ninja -D CMAKE_PREFIX_PATH=~/libs/QT6.5d -DCMAKE_WARN_DEPRECATED=OFF

but get the following warning while building my project with GCC12:

  /usr/include/c++/12/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. [-Wcpp]
     32 | #warning \
        |  ^~~~~~~

why doesn't CMAKE_WARN_DEPRECATED take an effect?

Running cmake with -Wno-deprecated also does not help.

cmake . -G Ninja -D CMAKE_PREFIX_PATH=~/libs/QT6.5d -Wno-deprecated

Solution

CMAKE_WARN_DEPRECATED controls CMake warnings (those emitted by message(DEPRECATION ...)), and passing -Wno-deprecated to CMake is an alias for setting this variable to OFF.

Your deprecation warning is issued by the compiler, and you need to pass the -Wno-deprecated flag to the compiler. One way to do this is to use target_compile_options:

target_compile_options(<target> [PRIVATE|PUBLIC] "-Wno-deprecated")

Answered By - You

Answer Checked By - Willingham (WPSolving Volunteer)