Apparently, command line to link executable is quite different from a
shared library (Modules/CMakeCXXInformation.cmake):
if(NOT CMAKE_CXX_LINK_EXECUTABLE)
set(CMAKE_CXX_LINK_EXECUTABLE
"<CMAKE_CXX_COMPILER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS>
<OBJECTS> -o <TARGET> <LINK_LIBRARIES>")
endif()
set(CMAKE_CXX_CREATE_SHARED_LIBRARY
"<CMAKE_CXX_COMPILER> <CMAKE_SHARED_LIBRARY_CXX_FLAGS>
<LANGUAGE_COMPILE_FLAGS> <LINK_FLAGS>
<CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS> <SONAME_FLAG><TARGET_SONAME>
-o <TARGET> <OBJECTS> <LINK_LIBRARIES>")
CMAKE_CXX_FLAGS/CMAKE_C_FLAGS which are filled into
<LANGUAGE_COMPILE_FLAGS> don't go into a linker command for
executable.
2015-01-22 19:11 GMT+03:00 Paul Smith <p...@mad-scientist.net>:
> I didn't get a response to the question below. I've since reproduced
> this with a simple test case; maybe someone can let me know why this
> difference appears and how I should handle it? I'm using cmake 3.1.0:
>
> Sample CMakeLists.txt:
>
> $ cat >CMakeLists.txt <<EOF
> cmake_minimum_required(VERSION 3.1.0)
> project(FlagTest)
> set(CMAKE_CXX_FLAGS -pthread)
> add_executable(foo foo.cpp)
> EOF
>
> $ echo 'int main(int argc, char**argv) { return 0; }' > foo.cpp
>
> On MacOSX with Xcode installed, I see the following behavior:
>
> $ cmake -G Xcode . && cmake --build . 2>&1 | tee xc.out
>
> In the output I see that the "-pthread" flag DOES appear on the compile
> line for "foo.o", but DOES NOT appear in the link line for "foo":
>
> $ grep pthread xc.out
> /.../clang -x c++ ... -pthread ... -c /.../foo.cpp -o /.../foo.o
>
> This is correct for clang, which does not want -pthread on the link line
> (unlike GCC, which wants it in both places). Now, I clean that up and
> try with the Makefile generator, and I see the following behavior:
>
> $ cmake -G 'Unix Makefiles' . && cmake --build . -- VERBOSE=1 2>&1 | tee
> mk.out
> clang: warning: argument unused during compilation: '-pthread'
>
> Now in this case we can see that the -pthread flag was added to BOTH the
> compile and the link line:
>
> $ grep pthread mk.out
> /usr/bin/c++ -pthread -o .../foo.cpp.o -c .../foo.cpp
> /usr/bin/c++ -pthread .../foo.cpp.o -o foo
> clang: warning: argument unused during compilation: '-pthread'
>
> This warning is totally bogus: it really means "unused during LINKING",
> but anyway: I'm not sure what to do to get rid of this warning: I need
> to support both Xcode and Makefiles on MacOSX (and Makefiles on Linux as
> well as both GCC and Clang).
>
> Is the intent that CMAKE_CXX_FLAGS only ever appear on the compile line?
> Or should it appear on both the compile and link lines? Is there an
> equivalent flag to CMAKE_EXE_LINKER_FLAGS that always applies only to
> compile lines, in all generators? Do we just have to continue to
> bastardize add_definitions() for this, maybe?
>
>
> On Thu, 2015-01-08 at 18:52 -0500, Paul Smith wrote:
>> If I'm on OSX, then when I set CMAKE_CXX_FLAGS and do not set
>> CMAKE_EXE_LINKER_FLAGS, for example, and I use the Xcode generator,
>> then
>> I see:
>> * CMAKE_CXX_FLAGS show up on the compilation line
>> * CMAKE_CXX_FLAGS do NOT show up in the linker line
>>
>> On the other hand if I'm on OSX and I use the Unix Makefiles
>> generator,
>> then I see:
>> * CMAKE_CXX_FLAGS show up on the compilation line
>> * CMAKE_CXX_FLAGS ALSO show up in the linker line
>>
>> I assume the Xcode output is correct and the makefile output (with
>> CMAKE_CXX_FLAGS in both) is not correct... but there's nothing I can
>> find in the docs that says this explicitly.
>>
>> I've printed the contents of the CMAKE_CXX_FLAGS and
>> CMAKE_EXE_LINKER_FLAGS at the end of my CMakeLists.txt and they're
>> just
>> what I expect. It's just that the link line has extra flags, when
>> invoked from make.
>
>
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