TheWin32 API provides several messages that return information about the characters and lines in an edit control. Most of the messages return an index, usually a zero-based number, to refer to a character or line. Given this, a single-line edit control containing n characters, the line index is zero and the characters are indexed from zero to n – 1. In a multiline edit control containing m lines and n characters, the lines are indexed from zero to m – 1, and the characters are indexed from zero to n – 1. Note that character indexing ignores line breaks.
An application can determine the number of characters in an edit control by sending the WM_GETTEXTLENGTH message to the edit control. This message returns the length, in characters (not including the terminating null character), of the text in a single-line or multiline edit control. The EM_LINELENGTH message returns the length, in characters, of a line specified by the character index of a character in the line. The returned length does not include any selected characters. An application can use these messages in a single-line or multiline edit control.
The EM_GETFIRSTVISIBLELINE message returns the zero-based index of the uppermost visible line in a multiline edit control, or the zero-based index of the first visible character in a single-line edit control. An application can copy a line from an edit control to a buffer by sending the EM_GETLINE message to the edit control. The line is specified by its line index and the first word of the receiving buffer contains the maximum number of bytes to be copied to the buffer. The return value is the number of bytes copied. This message can also be used in a single-line or multiline edit control.
There are unique messages available to return the information about a line in a multiline edit control. The EM_GETLINECOUNT message returns the number of lines in an edit control. An application can determine the index of a character in a specific line by using the EM_LINEFROMCHAR and EM_LINEINDEX messages. The EM_LINEFROMCHAR message returns the index of the line containing a specified character index. This message is the reverse of the EM_LINEINDEX message, which returns the index of the first character in a specified line.