CloseHandle

HANDLE hCom;
// but cCom didn't init by CreateFile
if (hCom == INVALID_HANDLE_VALUE)
CloseHandle(hCom);
Ref:
http://support.microsoft.com/kb/184352/zh-tw
http://www.aspfree.com/c/a/Code-Examples/Writing-a-Serial-Communication-Library-for-Windows/