How to Use Word and Line Break Information

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 CTRL+LEFT ARROW key and CTRL+RIGHT ARROW 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.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

Use Word and Line Break Information

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. Usually, in an edit control, a word break occurs only after delimiters. However, different rules apply to most Asian languages.

Word-break procedures for rich edit controls also group characters into character classes, each identified by a value in the range 0x00 through 0x0F. 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.doc" (before and after the period).

A character's class can be combined with zero or more word-break flags to form an 8-bit value. When performing word-wrap operations, a rich edit control uses word-break flags to determine where it can break lines. Rich Edit uses the following word-break flags.

FlagDescription
WBF_BREAKAFTERLines may be broken after the character.
WBF_BREAKLINEThe character is a delimiter. Delimiters mark the ends of words. Lines may be broken after delimiters.
WBF_ISWHITEThe 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 the default word-break procedure for a rich edit control with your own procedure by using the EM_SETWORDBREAKPROC message. For more information about word-break procedures, see the description of the EditWordBreakProc function.

Note  This replacement is not recommended for Microsoft Rich Edit 2.0 and later, due to the complexity of multilingual word breaking.
 

For Microsoft Rich Edit 1.0, 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. Note that Microsoft Rich Edit 2.0 and later do not support EditWordBreakProcEx, EM_GETWORDBREAKPROCEX, and EM_SETWORDBREAKPROCEX.

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.

Related topics

Using Rich Edit Controls
Windows common controls demo (CppWindowsCommonControls)

 

 

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