[CMake] Overriding CFLAGS/CXXFLAGS

[Paolo Zani]

I'm trying to set the CFLAGS/CXXFLAGS for a project to values that depend on
the compiler (and relative version) in use and the system CPU, detected
through the kwsys facilities, like this:


cmake_minimum_required (VERSION 2.6)

project(Dummy)

SET(KWSYS_NAMESPACE sys_info)
SET(KWSYS_USE_FundamentalType 1)
SET(KWSYS_USE_Process 1)
SET(KWSYS_USE_SystemInformation 1)
SUBDIRS(kwsys)

INCLUDE_DIRECTORIES(${CMAKE_BINARY_DIR}/kwsys)

TRY_RUN(COMPILE_RESULT RUN_RESULT
        ${PROJECT_BINARY_DIR}/CMakeTmp
        ${PROJECT_SOURCE_DIR}/flags_main.cpp
        CMAKE_FLAGS -DINCLUDE_DIRECTORIES:STRING=${CMAKE_BINARY_DIR}/kwsys
-DLINK_DIRECTORIES:STRING=${PROJECT_BINARY_DIR}/kwsys
-DLINK_LIBRARIES:STRING=${KWSYS_NAMESPACE}
        RUN_OUTPUT_VARIABLE RUN_OUTPUT)

[...]    # <---- OVERRIDE CFLAGS HERE

SUBDIRS(project_src)


with flags_main.cpp producing the appropriate flags line.

The problem with this approach is that TRY_RUN only gets executed when make
is invoked, and so far I haven't found a decent way of setting the flags so
that the contents of project_src gets built with the correct flags straight
away: using

SET(CMAKE_CXX_FLAGS_RELEASE ${RUN_OUTPUT} CACHE STRING blah FORCE)

won't work since it requires a (re)configuration to propagate the change,
while splitting the project in two, with a binary that generates a default
cache file to import with CMAKE_USER_MAKE_RULES_OVERRIDE doesn't seem an
option either (too bloated as an approach, and it requires different scripts
on different platforms).

Any suggestions?




-- 
Paolo Zani, PhD
VisLab.it - Artificial Vision and Intelligent Systems Lab.
Dipartimento di Ingegneria dell'Informazione
Università di Parma
via G.P. Usberti 181/A
I-43100  Parma - ITALY
web http://www.vislab.it/zani/
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