The following is an example of what C-M-\ does. This example is in C, and subsequent examples refer to it. The concepts in all examples in this section are applicable to most other languages; we cover analogous Lisp and Java features in the sections on modes for those languages.
Suppose you have the following C code:
int times (x, y)
int x, y;
{
int i;
int result = 0;
for (i = 0; i < x; i++)
{
result += y;
}
}
If you set mark at the beginning of this code, put the cursor at the end, and type C-M-\, Emacs formats it like this:
int times (x, y)
int x, y;
{
int i;
int result = 0;
for (i = 0; i < x; i++)
{
result += y;
}
}
C-M-\ is also handy for indenting an entire file according to your particular indentation style: you can just type C-x h (for mark-whole-buffer) followed by C-M-\.
M-m is handy for moving to the beginning of the actual code on a line. For example, assume your cursor is positioned like this:
int result = 0;
If you type M-m, it moves to the beginning of the int:
int result = 0;
As an example of M-^, let's say you want the opening curly brace for the for statement to appear on the same line as the for. Put the cursor anywhere on the line with the opening curly brace, type M-^, and the code looks like this:
for (i = 0; i < x; i++) {
result += y;
}
Language modes usually provide additional indentation commands that relate to specific features of the language. Having covered the general language mode concepts, we want to show you a few other general utilities: etags and font-lock mode. The etags facility helps programmers who work on large, multifile programs. All language modes can also take advantage of font-lock mode to make development more efficient.
9.2.4 etags
Another general feature of Emacs that applies to programmers is the etags facility.[61] etags works with code in many other languages as well, including Fortran, Java, Perl, Pascal, LATEX,, Lisp, and many assembly languages. If you work on large, multifile projects, you will find etags to be an enormous help.
etags is basically a multifile search facility that knows about C and Perl function definitions as well as searching in general. With it, you can find a function anywhere in an entire directory without having to remember in which file the function is defined, and you can do searches and query-replaces that span multiple files. etags uses tag tables, which contain lists of function names for each file in a directory along with information on where the functions' definitions are located within the files. Many of the commands associated with etags involve regular expressions (see Chapter 11) in search strings.
To use etags, you must first invoke the separate etags program in your current directory to create the tag table. Its arguments are the files for which you want tag information. The usual way to invoke it is etags *.[ch], that is, building a tag table from all files ending in .c or .h. (That's for you C programmers; other languages would use their appropriate extensions, of course.) You can run etags from shell mode or with the command M-! (for shell-command). The output of etags is the file TAGS, which is the tag table. When you are writing code, you can update your tag table to reflect new files and function definitions by invoking etags again.
After you have created the tag table, you need to make it known to Emacs. To do this, type M-x visit-tags-table Enter. This prompts you for the name of the tag table file; the default is TAGS in the current directory, as you would expect. After you execute this step, you can use the various Emacs tags commands.
The most important tag command is M-. (for find-tag). This command prompts you for a string to use in searching the tag table for a function whose name contains the string. Supply the search string, and Emacs visits the file containing the matching function name in the current window and goes to the first line of the function's definition. A variation of M-. is C-x 4 . (for find-tag-other-window), which uses another window instead of replacing the text in your current window.
A nice feature of M-. is that it picks up the word the cursor is on and uses it as the default search string. For example, if your cursor is anywhere on the string my_function, M-. uses my_function as the default. Thus, when you are looking at a C statement that calls a function, you can type M-. to see the code for that function.
If you have multiple functions with the same name, M-. finds the function in the file whose name comes first in alphabetical order. To find the others, you can use the command M-, (for tags-loop-continue) to find the next one (or complain if there are no more). This feature is especially useful if your directory contains more than one program, that is, if there is more than one function called main. M-, also has other uses, as we will see.
You can use the tag table to search for more than just function definitions. The command M-x tags-search Enter prompts for a regular expression; it searches through all files listed in the tag table (such as, all .c and .h files) for any occurrence of the regular expression, whether it is a function name or not. This capability is similar to the grep facility discussed earlier in this chapter. After you have invoked tags-search, you can find additional matches by typing M-,.
There is also an analogous query-replace capability. The command M-x tags-query-replace Enter does a regular expression query-replace (see Chapter 3) on all files listed in the tag table. As with the regular query-replace-regexp command, if you precede tags-query-replace with a prefix argument (i.e., C-u M-x tags-query-replace Enter), Emacs replaces only matches that are whole words. This feature is useful, for example, if you want to replace occurrences of printf without disturbing occurrences of fprintf. If you exit a tags-query-replace with Esc or C-g, you can resume it later by typing M-,.
61
etags is also a platform-specific feature. The etags facility is available on Unix platforms, including Mac OS X.