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# Q3SyntaxHighlighter Class Reference
[Qt3Support module]

The Q3SyntaxHighlighter class is a base class for implementing Q3TextEdit syntax highlighters. More...

     #include <Q3SyntaxHighlighter>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

- List of all members, including inherited members

### Public Functions

- Q3SyntaxHighlighter ( Q3TextEdit * textEdit )
- virtual ~Q3SyntaxHighlighter ()
- int currentParagraph () const
- virtual int highlightParagraph ( const QString & text, int endStateOfLastPara ) = 0
- void rehighlight ()
- void setFormat ( int start, int count, const QFont & font, const QColor & color )
- void setFormat ( int start, int count, const QColor & color )
- void setFormat ( int start, int count, const QFont & font )
- Q3TextEdit * textEdit () const

## Detailed Description

The Q3SyntaxHighlighter class is a base class for implementing Q3TextEdit syntax highlighters.

A syntax highligher automatically highlights parts of the text in a Q3TextEdit. Syntax highlighters are often used when the user is entering text in a specific format (for example, source code) and help the user to read the text and identify syntax errors.

To provide your own syntax highlighting for Q3TextEdit, you must subclass Q3SyntaxHighlighter and reimplement highlightParagraph().

When you create an instance of your Q3SyntaxHighlighter subclass, pass it the Q3TextEdit that you want the syntax highlighting to be applied to. After this your highlightParagraph() function will be called automatically whenever necessary. Use your highlightParagraph() function to apply formatting (e.g. setting the font and color) to the text that is passed to it.

## Member Function Documentation

### Q3SyntaxHighlighter::Q3SyntaxHighlighter ( Q3TextEdit * textEdit )

Constructs the Q3SyntaxHighlighter and installs it on textEdit. Ownership of the Q3SyntaxHighlighter is transferred to the textEdit

### Q3SyntaxHighlighter::~Q3SyntaxHighlighter () `[virtual]`

Destructor. Uninstalls this syntax highlighter from the textEdit()

### int Q3SyntaxHighlighter::currentParagraph () const

Returns the id of the paragraph which is highlighted, or -1 of no paragraph is currently highlighted.

Usually this function is called from within highlightParagraph().

### int Q3SyntaxHighlighter::highlightParagraph ( const QString & text, int endStateOfLastPara ) `[pure virtual]`

This function is called when necessary by the rich text engine, i.e. on paragraphs which have changed.

In your reimplementation you should parse the paragraph's text and call setFormat() as often as necessary to apply any font and color changes that you require. Your function must return a value which indicates the paragraph's end state: see below.

Some syntaxes can have constructs that span paragraphs. For example, a C++ syntax highlighter should be able to cope with `/``*...*``/` comments that span paragraphs. To deal with these cases it is necessary to know the end state of the previous paragraph (e.g. "in comment").

If your syntax does not have paragraph spanning constructs, simply ignore the endStateOfLastPara parameter and always return 0.

Whenever highlightParagraph() is called it is passed a value for endStateOfLastPara. For the very first paragraph this value is always -2. For any other paragraph the value is the value returned by the most recent highlightParagraph() call that applied to the preceding paragraph.

The value you return is up to you. We recommend only returning 0 (to signify that this paragraph's syntax highlighting does not affect the following paragraph), or a positive integer (to signify that this paragraph has ended in the middle of a paragraph spanning construct).

To find out which paragraph is highlighted, call currentParagraph().

For example, if you're writing a simple C++ syntax highlighter, you might designate 1 to signify "in comment". For a paragraph that ended in the middle of a comment you'd return 1, and for other paragraphs you'd return 0. In your parsing code if endStateOfLastPara was 1, you would highlight the text as a C++ comment until you reached the closing `*``/`.

### void Q3SyntaxHighlighter::rehighlight ()

Redoes the highlighting of the whole document.

### void Q3SyntaxHighlighter::setFormat ( int start, int count, const QFont & font, const QColor & color )

This function is applied to the syntax highlighter's current paragraph (the text of which is passed to the highlightParagraph() function).

The specified font and color are applied to the text from position start for count characters. (If count is 0, nothing is done.)

### void Q3SyntaxHighlighter::setFormat ( int start, int count, const QColor & color )

This is an overloaded member function, provided for convenience.

### void Q3SyntaxHighlighter::setFormat ( int start, int count, const QFont & font )

This is an overloaded member function, provided for convenience.

### Q3TextEdit * Q3SyntaxHighlighter::textEdit () const

Returns the Q3TextEdit on which this syntax highlighter is installed