Word and Line Breaks - Win32 Programmer's Reference

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Word and Line Breaks

A rich edit control calls a function called a word break procedure to find breaks between words and to determine where it can break lines. The control uses this information when performing word wrap operations and when processing the CTRL+LEFT and CTRL+RIGHT key combinations. An application can send messages to a rich edit control to replace the default word break procedure, to retrieve word break information, and to determine what line a given character falls on.

Word break procedures for rich edit controls are similar to those for edit controls, but they have additional capabilities. Word break procedures for both kinds of controls can determine whether a character is a delimiter and can find the nearest word break before or after the specified position. A delimiter is a character that marks the end of a word, such as a space. In an edit control, word breaks occur only after delimiters.

Word break procedures for rich edit controls also group characters into character classes, each identified by a value in the range 0x00 through 0x0F. Word breaks occur either after delimiters or between characters of different classes. Thus, a word break procedure with different classes for alphanumeric and punctuation characters would find two word breaks in the string "WIN.COM".

A character's class can be combined with zero or more word break flags to form an eight-bit value. When performing word wrap operations, a rich edit control uses word break flags to determine where it can break lines. There are the following word break flags.

WBF_BREAKAFTER	Lines may be broken after the character.
WBF_BREAKLINE	The character is a delimiter. Delimiters mark the ends of words. Lines may be broken after delimiters.
WBF_ISWHITE	The character is a white space character. Trailing white space characters are not included in the length of a line when wrapping.

The WBF_BREAKAFTER value is used to allow wrapping after a character that does not mark the end of a word, such as a hyphen.

You can replace a rich edit control's default word break procedure with your own by using the EM_SETWORDBREAKPROC message. For more information about word break procedures, see the description of the EditWordBreakProc function.

Alternately, you can use the EM_SETWORDBREAKPROCEX message to replace the default extended word break procedure with an EditWordBreakProcEx function. This function provides additional information about the text, such as the character set. You can use the EM_GETWORDBREAKPROCEX message to retrieve the address of the current extended word break procedure.

You can use the EM_FINDWORDBREAK message to find word breaks or to determine a character's class and word break flags. In turn, the control calls its word break procedure to get the requested information.

To determine which line a given character falls on, you can use the EM_EXLINEFROMCHAR message.

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