[CMake] Removing compiler flags for GCC for specific target (3 methods that don't work right)

[Ryan Pavlik]

On 5/11/2010 9:52 AM, Alok Govil wrote:
> Hi all,
>
> I am setting CMAKE_CXX_FLAGS to "-Wall -ansi -pedantic" but would like 
> to remove these flags for compilation
> of UnitTest++.  I tried three methods of doing this with some issue 
> with each:
>
> 1.   string (REPLACE "-Wall" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
>      # And likewise for -ansi and -pedantic
>
> 2.   set (CMAKE_CXX_FLAGS "")
>
> 3.   unset (CMAKE_CXX_FLAGS CACHE)
>
> I am doing the above for both CMAKE_CXX_FLAGS and CMAKE_C_FLAGS.
>
> The problem with 1 and 2 is that they are not working.  GCC 
> (MinGW-W32) still gives the concerned warnings.  I do not get these 
> warnings if I do not set these flags at all to begin with.
>
> Method 3 does work.  The problem however is that it removes 
> CMAKE_CXX_FLAGS globally, not just from CMakeList.txt for UnitTest++.  
> I could in principle recreate CMAKE_CXX_FLAGS but would like to 
> understand what's going on first.
>
> Method 1 worked well for MSVC (using different flags than for GCC).
>
> Here are all my files with relevant lines (shown only for 
> CMAKE_CXX_FLAGS but done also for CMAKE_C_FLAGS):
>
> _CXX_Flag_Overrides.cmake_:
>     # ...
>     if (CMAKE_COMPILER_IS_GNUCXX)
>         # message ("CMAKE_COMPILER_IS_GNUCXX")
>         set(CMAKE_CXX_FLAGS_INIT "${CMAKE_CXX_FLAGS_INIT} -Wall -ansi 
> -pedantic")
>     endif()
>     # ...
>
> _CMakeLists.txt (top-level)_
>     # ...
>     set(CMAKE_USER_MAKE_RULES_OVERRIDE_CXX 
> ${CMAKE_CURRENT_SOURCE_DIR}/CXX_Flag_Overrides.cmake)
>     project (projectname)
>     # ...
>     add_subdirectory (UnitTest++)
>     # ...
>
> _CMakeLists.txt (UnitTest++)_
>     # ...
>     if (CMAKE_COMPILER_IS_GNUCXX) # 
> http://www.cmake.org/cmake/help/cmake-2-8-docs.html#variable:CMAKE_COMPILER_IS_GNULANG
>         message ("CMAKE_COMPILER_IS_GNUCXX")
> #string (REPLACE "-Wall" ""     CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
>         #string (REPLACE "-ansi" ""     CMAKE_CXX_FLAGS 
> ${CMAKE_CXX_FLAGS})
>         #string (REPLACE "-pedantic" "" CMAKE_CXX_FLAGS 
> ${CMAKE_CXX_FLAGS})
>         #unset (CMAKE_CXX_FLAGS CACHE)
>         set (CMAKE_CXX_FLAGS "")
>         message ("${CMAKE_CXX_FLAGS}")
>     endif()
>     # ...
>     add_library (UnitTest++ ${Sources})
>
> Thanks,
>
> Alok


You might consider using the target property COMPILE_FLAGS as a more 
fine-grained way to control the flags, instead of the build-wide 
variable.  See the help for more info.

Ryan
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