The command M-x tags-apropos rounds out the search facilities of etags. If you give it a regular expression argument, it opens a *Tags List* buffer that contains a list of all tags in the tag table (including names of files as well as functions) that match the regular expression. For example, if you want to find out the names of output routines in a multiple-file C program, you could invoke tags-apropos with the argument print or write.
Finally, you can type M-x list-tags Enter to list all the tags in the table—that is, all the functions—for a given C file. Supply the filename at the prompt, and you get a *Tags List* buffer showing the names of functions defined in that file along with their return types (if any). Note that if you move your cursor to this list, you can use M-. to look at the actual code for the function. M-. picks up the word the cursor is on as the default function name, so you can just move the cursor to the name of the function you want to see and press M-. followed by Enter to see it.
9.2.5 Fonts and Font-lock Mode
There's one last common feature to mention. The use of fonts to help present code is very popular—so popular, in fact, that it is now universal. Unlike the indentation and formatting supported by the various language modes, nothing in the code itself changes. But when you're in font-lock mode, your program certainly looks different.
You can turn on this feature for any language mode with M-x font-lock-mode to see for yourself. Keywords get a particular color; comments get a different color and are often italicized; strings and literals get yet another color. It can aid quick browsing of code. Many people come to depend on it much the way they rely on proper indentation. If you become one of those people, you'll want to make it the default for all language sessions. You can add the following line to your .emacs file to achieve this aim:
;; Turn on font-locking globally
(global-font-lock-mode t)
The colors and styles used are customizable if you don't like the defaults. M-x list-faces-display produces a list of the named faces Emacs knows about. You'll see something similar to the screen shown in Figure 9-1.
Figure 9-1. Fonts available for customization in Emacs
Of course, in real life, the colors and bold and whatnot should be more pronounced. You'll also see quite a few more faces. You can modify any of those faces with either M-x modify-face (a simple prompted "wizard" approach) or M-x customize-face (the big fancy interactive approach). You can also add lines to your .emacs file for your favorite customizations. Here's an example:
'(font-lock-comment-face
((((class color) (background light))
(:foreground "Firebrick" :slant italic)))))
Note that not all displays support all of the possible variations of bold, italic, underline, colors, and so on. This is a classic case of "your mileage may vary." Still, with the ability to customize it all yourself, you should be able to find a combination that works well on your system.
The remaining sections in this chapter deal with several of the language-specific modes including JDEE, a suite of packages devoted to the world of Java development in Emacs.
You need not read all of these sections if you are interested in only one or two of the languages. If you program in another language for which Emacs has a mode, you may want to read one of the following sections to get the "flavor" of a language mode; all language modes have the same basic concepts, so this should get you off to a good start. Indeed, many language modes use another mode as a base. For example, Java mode is really just an extension of C mode.
9.3 C and C++ Support
Emacs automatically enters C mode when you visit a file whose suffix is .c, .h, .y (for yacc grammars), or .lex (lex specification files). Emacs invokes C++ mode when you visit a file whose suffix is .C, .H, .cc, .hh, .cpp, .cxx, .hxx, .c++, or .h++. You can also put any file in C mode manually by typing M-x c-mode Enter. Similarly, you can use c++-mode to put a buffer into C++ mode.
Both C and C++ modes are implemented in the same Emacs Lisp package, called cc-mode,[62] which also includes a mode for the Objective-C language used in Mac OS X. C mode understands both ANSI C and the older Kernighan and Ritchie C syntax. We describe C mode functions, but you should assume that everything also applies to C++ mode. C++ mode has a small number of additional features, which we describe at the end of this section.
We should also note that the Emacs mode for Perl is derived from an older version of C mode. If you program in Perl, you will find that virtually all of the motion, indentation, and formatting commands in C mode apply equally to Perl mode, with perl- replacing c- in their names. Emacs invokes Perl mode on files with suffix .pl. (However, to be honest we prefer CPerl mode, discussed later in this chapter.)
In C mode, Emacs understands the syntax elements described earlier in this chapter. The characters semicolon (;), colon (:), comma (,) curly braces ({ and }), and pound sign (#, for C preprocessor commands) are all electric, meaning that Emacs automatically indents the current line when you type them. It also actively uses the font options when you have font-lock mode turned on.
9.3.1 Motion Commands
In addition to the standard Emacs commands for words and sentences (which are mainly useful only inside multiline comments), C mode contains advanced commands that know about statements, functions,[63] and preprocessor conditionals. A summary of these commands appears in Table 9-3.
Table 9-3. Advanced C motion commands
| Keystrokes | Command name | Action |
|---|---|---|
| M-a | c-beginning-of-statement | Move to the beginning of the current statement. |
| M-e | c-end-of-statement | Move to the end of the current statement. |
| M-q | c-fill-paragraph | If in comment, fill the paragraph, preserving indentations and decorations. |
| C-M-a | beginning-of-defun | Move to the beginning of the body of the function surrounding the point. |
| C-M-e | end-of-defun | Move to the end of the function. |
| C-M-h | c-mark-function | Put the cursor at the beginning of the function, the mark at the end. |
| C-c C-q | c-indent-defun | Indent the entire function according to indentation style. |
| C-c C-u | c-up-conditional | Move to the beginning of the current preprocessor conditional. |
| C-c C-p | c-backward-conditional | Move to the previous preprocessor conditional. |
| C-c C-n | c-forward-conditional | Move to the next preprocessor conditional. |
62
We know! There is no M-x cc-mode. It can be confusing. Just try to remember that the modes are named directly after the language they support.
63
The function commands have "defun" in their names because they are actually adaptations of analogous commands in Lisp mode; a defun is a function definition in Lisp.