Windows XP Pro 32bit
Visual studio 2008 VC Express edition.
I have installed cmake and created the CMakeLists.txt and I want to cross-platform for Linux/wind
Your CMakeLists.txt defines compile flag -Wextra for GCC and then CMake tried to use that on cl (the Microsoft compiler) too. Fix the CMakeLists.txt so that it tests for compiler before setting warning flags, i.e.
# Set default compile flags for GCC
if(CMAKE_COMPILER_IS_GNUCXX)
message(STATUS "GCC detected, adding compile flags")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++98 -pedantic -Wall -Wextra")
endif(CMAKE_COMPILER_IS_GNUCXX)