C语言编程规范_Linux

Linux kernel coding style

This is a short document describing the preferred coding style for the linux kernel. Coding style is very personal, and I won't _force_ my views on anybody, but this is what goes for anything that I have to be able to maintain, and I'd prefer it for most other things too. Please at least consider the points made here.

First off, I'd suggest printing out a copy of the GNU coding standards, and NOT read it. Burn them, it's a great symbolic gesture.

Anyway, here goes:

Chapter 1: Indentation

Tabs are 8 characters, and thus indentations are also 8 characters. There are heretic movements that try to make indentations 4 (or even 2!) characters deep, and that is akin to trying to define the value of PI to be 3.

Rationale: The whole idea behind indentation is to clearly define where a block of control starts and ends. Especially when you've been looking at your screen for 20 straight hours, you'll find it a lot easier to see how the indentation works if you have large indentations.

Now, some people will claim that having 8-character indentations makes the code move too far to the right, and makes it hard to read on a 80-character terminal screen. The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program.

In short, 8-char indents make things easier to read, and have the added benefit of warning you when you're nesting your functions too deep. Heed that warning.

The preferred way to ease multiple indentation levels in a switch statement is

to align the "switch" and its subordinate "case" labels in the same column instead of "double-indenting" the "case" labels. E.g.:

switch (suffix) {

case 'G':

case 'g':

mem <<= 30;

break;

case 'M':

case 'm':

mem <<= 20;

break;

case 'K':

case 'k':

mem <<= 10;

/* fall through */

default:

break;

}

Don't put multiple statements on a single line unless you have something to hide:

if (condition) do_this;

do_something_everytime;

Don't put multiple assignments on a single line either. Kernel coding style

is super simple. Avoid tricky expressions.

Outside of comments, documentation and except in Kconfig, spaces are never used for indentation, and the above example is deliberately broken.

Get a decent editor and don't leave whitespace at the end of lines.

Chapter 2: Breaking long lines and strings

Coding style is all about readability and maintainability using commonly available tools.

The limit on the length of lines is 80 columns and this is a strongly preferred limit.

Statements longer than 80 columns will be broken into sensible chunks. Descendants are always substantially shorter than the parent and are placed

substantially to the right. The same applies to function headers with a long

argument list. Long strings are as well broken into shorter strings. The only exception to this is where exceeding 80 columns significantly increases

readability and does not hide information.

void fun(int a, int b, int c)

{

if (condition)

printk(KERN_WARNING "Warning this is a long printk with "

"3 parameters a: %u b: %u "

"c: %u \n", a, b, c); else

next_statement;

}

Chapter 3: Placing Braces and Spaces

The other issue that always comes up in C styling is the placement of braces. Unlike the indent size, there are few technical reasons to choose one placement strategy over the other, but the preferred way, as shown to us by the prophets Kernighan and Ritchie, is to put the opening brace last on the line, and put the closing brace first, thusly:

if (x is true) {

we do y

}

This applies to all non-function statement blocks (if, switch, for, while, do). E.g.:

switch (action) {

case KOBJ_ADD:

return "add";

case KOBJ_REMOVE:

return "remove";

case KOBJ_CHANGE:

return "change";

default:

return NULL;

}

However, there is one special case, namely functions: they have the

opening brace at the beginning of the next line, thus:

int function(int x)

{

body of function

}

Heretic people all over the world have claimed that this inconsistency is ... well ... inconsistent, but all right-thinking people know that (a) K&R are _right_ and (b) K&R are right. Besides, functions are special anyway (you can't nest them in C).

Note that the closing brace is empty on a line of its own, _except_ in the cases where it is followed by a continuation of the same statement, ie a "while" in a do-statement or an "else" in an if-statement, like this:

do {

body of do-loop

} while (condition);

and

if (x == y) {

..

} else if (x > y) {

...

} else {

....

}

Rationale: K&R.

Also, note that this brace-placement also minimizes the number of empty (or almost empty) lines, without any loss of readability. Thus, as the supply of new-lines on your screen is not a renewable resource (think 25-line terminal screens here), you have more empty lines to put comments on.

Do not unnecessarily use braces where a single statement will do.

if (condition)

action();

This does not apply if one branch of a conditional statement is a single statement. Use braces in both branches.

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