int LineIndex( int nLine = -1 ) const;
nLine
Contains the index value for the desired character in the text of the edit control, or contains -1. If nLine is -1, it specifies the current line, i.e., the line that contains the caret.
Retrieves the character index of a line within a multiple-line edit control. The character index is the number of characters from the beginning of the edit control to the specified line.
This member function is only processed by multiple-line edit controls.
The character index of the line specified in nLine, or -1 if the specified line number is greater then the number of lines in the edit control.
CEdit::LineFromChar, EM_LINEINDEX