Debra Cameron - Learning GNU Emacs, 3rd Edition

Because }is a parenthesis-type character, Emacs attempts to "flash" a matching {when you type }. If the matching {is outside of the text displayed in your window, Emacs instead prints the line containing the {in the minibuffer. Furthermore, if only whitespace (blanks or tabs) follows the {on its line, Emacs also prints a ^J(for C-j) followed by the next line, thus giving a better idea of the context of the {.

Recall the "times" example earlier in this chapter. Let's say you are typing in a }to end the function, and the {that begins the function body is off-screen. There is no code on the line following the beginning {, so you see the following in the minibuffer after you type }:

Matches {^J int i;

Coding style in C—or any programming language for that matter—is a very personal thing. C programmers learn from various books or by referring to various different pieces of other people's code; eventually they evolve a personal style that may or may not conform to those that they learned from.

C mode provides a rich set of features for customizing its indentation behavior that mirrors this way of learning the language. At the simplest level, you can choose a coding style by name. Then, if you're not satisfied, you can customize your chosen style or even create your own from scratch. The latter tasks, however, require a fair amount of Emacs Lisp programming knowledge (see Chapter 11) and perhaps a bit of bravery.

You can choose a named coding style with the command M-x c-set-style. This command prompts you for the name of the style you want. The easiest thing to do at this point is to type Tab, the completion character (see Chapter 14 Chapter 14. The Help System Emacs has the most comprehensive help facility of any text editor—and one of the best such facilities of any program at all. In fact, the Emacs help facilities probably cut down the time it took for us to write this book by an order of magnitude, and they can help you immeasurably in your ongoing quest to learn more about Emacs. In this chapter, we describe Emacs help in the following areas: • The tutorial. • The help key ( C-h ) and Help menu, which allow you to get help on a wide variety of topics. • The help facilities of complex commands like query-replace and dired . • Navigating Emacs manuals and using the info documentation reader. • Completion , in which Emacs helps you finish typing names of functions, variables, filenames, and more. Completion not only saves you time and helps you complete names of functions you know about but can help you discover new commands and variables. ), which brings up a *Completions*window that lists all of the choices. Type one of them and press Enterto select it.

By default, Emacs comes loaded with the styles shown in Table 9-4.

Table 9-4. Built-in cc-mode indentation styles

To show how some of these styles work, let's start with the C function example from earlier in this chapter:

int times (x, y)

int x, y;

{

int i;

int result = 0;

for (i = 0; i < x; i++)

{

result += y;

}

}

If you define a region around this code and you type C-M-\(for indent-region), Emacs reformats the code in the default style like this:

int times (x, y)

int x, y;

{

int i;

int result = 0;

for (i = 0; i < x; i++)

{

result += y;

}

}

If you type C-c. (for c-set-style), enter k&r, and then repeat the reformatting, the code looks like this:

int times (x, y)

int x, y;

{

int i;

int result = 0;

for (i = 0; i < x; i++)

{

result += y;

}

}

Or, if you want to switch to GNU-style indentation, choose the style gnuand reformat. The result is:

int times (x, y)

int x, y;

{

int i;

int result = 0;

for (i = 0; i < x; i++)

{

result += y;

}

}

Once you decide on a coding style, you can set it up permanently by putting a line in your .emacs file that looks like this:

(add-hook 'c-mode-hook

'(lambda ( )

(c-set-style " stylename ")))

Unfortunately, we'll have to wait until Chapter 11to understand exactly what this code does. For now, make sure that you insert a single quote (') before the (lambdain the second line.

Each coding style contains subtleties that makes it nontrivial for Emacs to implement. Older versions of Emacs did this by defining several variables that controlled various indentation levels; these were not easy to work with and, frankly, did not really cover 100 percent of the nuances of each style. The current version of C mode, in contrast, uses a considerably larger set of variables—too large, in fact, for anyone other than hardy Emacs Lisp hackers to deal with.

Therefore, C mode keeps track of groups of these variables and their values under named styles. One huge variable, called c-style-alist, contains all of the styles and their associated information. You can customize this beast either by changing values of variables within existing styles or by adding a style of your own. For further details, look in the file cc-mode.el in your system's Emacs Lisp directory (see Chapter 11).

C mode contains a number of other useful features, ranging from the generally useful to the arcanely obscure. Perhaps the most interesting of these are two ways of adding additional electric functionality to certain keystrokes, called auto-newline and hungry-delete-key . [64]