学步园

原文地址：http://www.gnu.org/software/emacs/manual/html_node/emacs/Specifying-File-Variables.html

有空再翻译一下，一个简单的应用的例子，编译一个简单的opencv程序：

#include <opencv2/opencv.hpp>
#include <stdio.h>
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char **argv)
{
  Mat image;
  image = imread(argv[1],1);
 
  if(argc != 2 || !image.data)
    {
      printf("No image data\n");
      return -1;
    }

  String winName = "Image";
  namedWindow(winName, CV_WINDOW_AUTOSIZE);
  imshow(winName,image);

  waitKey(0);
  return 0;
}

//下面这几行为emacs设定本地变量compile-command，用emacs打开此文件，并用M-x compile命令时，编译命令就会成为外我们设定的
//需要注意的是必须是相应编程语言的注释形式来包含这几句，如c语言需要/* */来包含每一行，本例是c++所以是//
//否则会出现emacs local-variables error: (error "Local variables entry is missing the suffix")错误
//另外需要放到文件第一行或文件末，放到文件末格式如下；放到文件头格式用-*-  -*-包含。
//还有就是输入后，必须重新打开一次文件或者用revert-buffer命令重新载入，才能使用，这些是在打开文件时被emacs解析的。
// Local Variables:
// compile-command: "g++ -o di DisplayImage.cpp `pkg-config --libs --cflags opencv`"
// End:

48.2.4.1 Specifying File Variables

There are two ways to specify file local variable values: in the first line, or with a local variables list. Here's how to specify them in the first line:

     -*- mode: modename; var: value; ... -*-

You can specify any number of variable/value pairs in this way, each pair with a colon and semicolon. The special variable/value pair mode: modename;,
if present, specifies a major mode. The values are used literally, and not evaluated.

You
can use M-x add-file-local-variable-prop-line instead of adding entries by hand. This command prompts for a variable and value, and adds them to the first line in the appropriate way. M-x delete-file-local-variable-prop-line prompts
for a variable, and deletes its entry from the line. The command M-x copy-dir-locals-to-file-locals-prop-line copies the current directory-local variables to the first line (see Directory
Variables).

Here is an example first line that specifies Lisp mode and sets two variables with numeric values:

     ;; -*- mode: Lisp; fill-column: 75; comment-column: 50; -*-

Aside from mode, other keywords that have special meanings as file variables are coding, unibyte,
and eval. These are described below.

In shell scripts, the first line is used to identify the script interpreter, so you cannot put any local variables there. To
accommodate this, Emacs looks for local variable specifications in the second line if the first line specifies an interpreter. The same is true for man pages which start with the magic string ‘'\"’ to specify
a list of troff preprocessors (not all do, however).

Apart from using a ‘-*-’ line, you can define file local variables using a local variables list near the end of the file. The start of the local variables list should be no more than
3000 characters from the end of the file, and must be on the last page if the file is divided into pages.

If a file has both a local variables list and a ‘-*-’ line, Emacs processes everything in the ‘-*-’ line first, and everything in the local variables list afterward.
The exception to this is a major mode specification. Emacs applies this first, wherever it appears, since most major modes kill all local variables as part of their initialization.

A local variables list starts with a line containing the string ‘Local Variables:’, and ends with a line containing the string ‘End:’. In between come the variable names and values,
one set per line, like this:

     /* Local Variables:  */
     /* mode: c           */
     /* comment-column: 0 */
     /* End:              */

In this example, each line starts with the prefix ‘/*’ and ends with the suffix ‘*/’. Emacs recognizes the prefix and suffix by finding them surrounding the magic string ‘Local
Variables:’, on the first line of the list; it then automatically discards them from the other lines of the list. The usual reason for using a prefix and/or suffix is to embed the local variables list in a comment, so it won't confuse other programs
that the file is intended for. The example above is for the C programming language, where comments start with ‘/*’ and end with ‘*/’.

Instead of typing in the local variables list directly,
you can use the command M-x add-file-local-variable. This prompts for a variable and value, and adds them to the list, adding the ‘Local Variables:’ string and start and end markers
as necessary. The command M-x delete-file-local-variable deletes a variable from the list. M-x copy-dir-locals-to-file-locals copies directory-local variables to the list (see Directory
Variables).

As with the ‘-*-’ line, the variables in a local variables list are used literally, and are not evaluated first. If you want to split a long string value across multiple lines of the file, you can use backslash-newline,
which is ignored in Lisp string constants; you should put the prefix and suffix on each line, even lines that start or end within the string, as they will be stripped off when processing the list. Here is an example:

     # Local Variables:
     # compile-command: "cc foo.c -Dfoo=bar -Dhack=whatever \
     #   -Dmumble=blaah"
     # End:

Some “variable names” have special meanings in a local variables list:

• mode enables the specified major mode.
• eval evaluates the specified Lisp expression (the value returned by that expression is ignored).
• coding specifies the coding system for character code conversion of this file. See Coding
  Systems.
• unibyte says to load or compile a file of Emacs Lisp in unibyte mode, if the value is t.
  See Disabling Multibyte.

These four keywords are not really variables; setting them in any other context has no special meaning.

Do not use the mode keyword for minor modes. To enable or disable a minor mode in a local variables list, use the eval keyword
with a Lisp expression that runs the mode command (see Minor Modes). For example, the following local variables list enables Eldoc mode
(see Lisp Doc) by calling eldoc-modewith no argument (calling
it with an argument of 1 would do the same), and disables Font Lock mode (see Font Lock) by calling font-lock-mode with
an argument of -1.

     ;; Local Variables:
     ;; eval: (eldoc-mode)
     ;; eval: (font-lock-mode -1)
     ;; End:

Note, however, that it is often a mistake to specify minor modes this way. Minor modes represent individual user preferences, and it may be inappropriate to impose your preferences on another user who might edit the file. If you wish to automatically enable
or disable a minor mode in a situation-dependent way, it is often better to do it in a major mode hook (see Hooks).

Use the command M-x normal-mode to reset the local variables and major mode of a buffer according to the file name and contents, including the local variables list if any. See Choosing
Modes.