[CMake] Stray backslash appearing when CMAKE_CXX_FLAGS_RELEASE used in custom command
On 1 November at 10:02, Stephen Morris wrote:
> My approach is basically to set up a custom command thus:
> set(CXX_FLAGS ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_DEBUG}) .. or whatever,
> depending on the current configuration..
> get_target_property(compile_options, mytarget, COMPILE_OPTIONS)
> add_custom_command(OUTPUT myheader.h.gch
> COMMAND ${CMAKE_CXX_COMPILER}
> ${CXX_FLAGS} ${compile_options} -fPIC -std=gnu++17 -c myheader.h -o
> myheader.h.gch
> DEPENDS myheader.h)
> add_custom_target(BuildMyPCH
> DEPENDS myheader.h.gch)
> add_dependencies(mytarget, BuildMyPCH)
My earlier question still stands, but at the time I wrote it I had only tested
it for Debug builds where ${CMAKE_CXX_FLAGS_DEBUG} consisted of a single item,
'-g'.
I've since tried doing the same thing for a Release build, and this failed
because ${CMAKE_CXX_FLAGS_RELEASE} has two items, '-O3 -DNDEBUG'. When the
custom command is executed, this somehow becomes "-O3\ -DNDEBUG" on the command
line, and the presence of the stray backslash causes the compilation to fail
with the message,
"cc1plus: error: argument to '-O' should be a non-negative integer. 'g', 's' or
'fast'"
So why isn't the cmake variable placed properly onto the command line, and what
can I do to prevent this behaviour?
--
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[CMake] Accessing -fPIC and -std settings within CMake definitions
I'm setting up a custom build step to build a precompiled header in gcc (yes I
know that native support is coming with CMake 3.16, but I need to get something
working on an older version).
My approach is basically to set up a custom command thus:
set_target_properties(mytarget PRIVATE CXX_STANDARD 17)
set_target_properties(mytarget PRIVATE POSITION_INDEPENDENT CODE_1)
set(CMAKE_VERBOSE_MAKEFILE TRUE)
...
...
set(CXX_FLAGS ${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_DEBUG}) .. or whatever,
depending on the current configuration..
get_target_property(compile_options, mytarget, COMPILE_OPTIONS)
add_custom_command(OUTPUT myheader.h.gch
COMMAND ${CMAKE_CXX_COMPILER}
${CXX_FLAGS} ${compile_options} -fPIC -std=gnu++17 -c myheader.h -o
myheader.h.gch
DEPENDS myheader.h)
add_custom_target(BuildMyPCH
DEPENDS myheader.h.gch)
add_dependencies(mytarget, BuildMyPCH)
You'll note that in my custom command I've had to specify -fPIC and
-std-gnu++17 explicitly, because they aren't included among either CXX_FLAGS or
COMPILE_OPTIONS. I've looked for them among the COMPILE_DEFINITIONS,
COMPILE_FEATURES and COMPILE_FLAGS properties of my target as well, but there's
no sign of them. And yet if I look at the verbose output when gcc builds other
files using the CMake-generated makefile, I see that they are being included
automatically.
So, my question: where is CMake storing these settings, and how can I apply
them in my custom command without having to do so manually?
--
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