TextInput Backspace on Win32


I use SDL 2.0.9 to build my win32 program.
I need input Chinese character, but my input method’s Candidate List not shown.
So, I found a way on web forums which to fix it with Compiling SDL with #define SDL_DISABLE_WINDOWS_IME in SDL_windowskeyboard.c

I follow the link:

Sure, it works!
But there is another problem, the Backspace event.

When user typing Chinese characters, first character will be display on the input method’s composition box.
If user satisfactory, he press space bar, the Chinese character will be to the input box.
If user not satisfactory, he can use Backspace to erase the character which input to composition box.

But, when the user use Backspace to erase the characters in composition box, my program also can receive the Backspace key event, so the characters already in input box will be erase.

I question is how to distinction the Backspace key for input method’s composition or for keyboard event just.