The EM_EXLINEFROMCHAR message determines which line contains the specified character in a rich edit control.
EM_EXLINEFROMCHAR
wParam = 0;
lParam = (LPARAM) (DWORD) ichCharPos;
Returns the zero-based index of the line.
Windows NT: Requires version 3.51 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in richedit.h.
Rich Edit Controls Overview, Rich Edit Messages