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5.1 Font Locking Preliminaries

The font locking for most of the CC Mode languages were provided directly by the Font Lock package prior to version 5.30 of CC Mode. In the transition to CC Mode the patterns have been reworked completely and are applied uniformly across all the languages except AWK mode, just like the indentation rules (although each language still has some peculiarities of its own, of course). Since the languages previously had completely separate font locking patterns, this means that it’s a bit different in most languages now.

The main goal for the font locking in CC Mode is accuracy, to provide a dependable aid in recognizing the various constructs. Some, like strings and comments, are easy to recognize while others, like declarations and types, can be very tricky. CC Mode can go to great lengths to recognize declarations and casts correctly, especially when the types aren’t recognized by standard patterns. This is a fairly demanding analysis which can be slow on older hardware, and it can therefore be disabled by choosing a lower decoration level with the variable font-lock-maximum-decoration (see Font Lock in GNU Emacs Manual).

The decoration levels are used as follows:

  1. Minimal font locking: Fontify only comments, strings and preprocessor directives (in the languages that use cpp).
  2. Fast font locking: In addition to level 1, fontify keywords, simple types and declarations that are easy to recognize. The variables *-font-lock-extra-types (where ‘*’ is the name of the language) are used to recognize types (see below). Documentation comments like Javadoc are fontified according to c-doc-comment-style (see Documentation Comments).

    Use this if you think the font locking is too slow. It’s the closest corresponding level to level 3 in the old font lock patterns.

  3. Accurate font locking: Like level 2 but uses a different approach that can recognize types and declarations much more accurately. The *-font-lock-extra-types variables are still used, but user defined types are recognized correctly anyway in most cases. Therefore those variables should be fairly restrictive and not contain patterns that are uncertain.

    This level is designed for fairly modern hardware and a font lock support mode like Lazy Lock or Just-in-time Lock mode that only fontifies the parts that are actually shown. Fontifying the whole buffer at once can easily get bothersomely slow even on contemporary hardware. See Font Lock in GNU Emacs Manual.

Since user defined types are hard to recognize you can provide additional regexps to match those you use:

User Option: c-font-lock-extra-types
User Option: c++-font-lock-extra-types
User Option: objc-font-lock-extra-types
User Option: java-font-lock-extra-types
User Option: idl-font-lock-extra-types
User Option: pike-font-lock-extra-types

For each language there’s a variable *-font-lock-extra-types, where ‘*’ stands for the language in question. It contains a list of regexps that matches identifiers that should be recognized as types, e.g., ‘\\sw+_t’ to recognize all identifiers ending with ‘_t’ as is customary in C code. Each regexp should not match more than a single identifier.

The default values contain regexps for many types in standard runtime libraries that are otherwise difficult to recognize, and patterns for standard type naming conventions like the ‘_t’ suffix in C and C++. Java, Objective-C and Pike have as a convention to start class names with capitals, so there are patterns for that in those languages.

Despite the names of these variables, they are not only used for fontification but in other places as well where CC Mode needs to recognize types.

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