I can achieve this by gcc :
gcc -mwindows -o simple simple.c
But only find this in cmake:
add_executable(simple WIN32 simple.c)
But it's not exactly the same as -mwindows,
this will require the entry point to be WinMain,
while gcc -mwindows doesn't require this(can be main).
How should I do it properly?
If you use:
add_executable(simple WIN32 simple.c)
then you must provide a WinMain function. That's what the WIN32 flag to add_executable means: it means you're going to make it a Windows program, and provide a WinMain function.
I would recommend doing it this way if you're really writing a Windows application. It's what makes the most sense and fits most naturally with the underlying OS.
However, if you still want to pass gcc the "-mwindows" flag, but use a "main" anyway, then simply add "-mwindows" to the CMAKE_CXX_FLAGS and/or CMAKE_C_FLAGS value. You can do this in the cmake-gui program by adjusting those variables interactively to include "-mwindows" or you can do it with command line CMake, like this:
cmake -DCMAKE_C_FLAGS="-mwindows"
As DLRdave has said saying that the executable will be a win32 one means it will have WinMain as the entry point and be a windows application.
If the application is to be cross platform still then the usual means to suppress the console window but still allow use of main is to write a stub WinMain as found in the SDL or SFML libraries which simply calls the main function with the global variables __argc and __argv as arguments and returns its result.
This prevents the application from having a console window but reduces the disruption to the code of having to use WinMain as the entry point.
You can add target link option (for new versions of Cmake)
target_link_options(simple PRIVATE -mwindows)
https://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/i386-and-x86_002d64-Windows-Options.html
