~vcs-imports/busybox/trunk : revision 697

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Busybox Style Guide

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===================

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This document describes the coding style conventions used in Busybox. If you

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add a new file to Busybox or are editing an existing file, please format your

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code according to this style. If you are the maintainer of a file that does

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not follow these guidelines, please -- at your own convenience -- modify the

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file(s) you maintain to bring them into conformance with this style guide.

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Please note that this is a low priority task.

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To help you format the whitespace of your programs, an ".indent.pro" file is

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included in the main Busybox source directory that contains option flags to

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format code as per this style guide. This way you can run GNU indent on your

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files by typing 'indent myfile.c myfile.h' and it will magically apply all the

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right formatting rules to your file. Please _do_not_ run this on all the files

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in the directory, just your own.

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Declaration Order

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-----------------

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Here is the order in which code should be laid out in a file:

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- commented author name and email address(es)

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- commented GPL boilerplate

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- commented description of program

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- #includes and #defines

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- const and globals variables

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- function declarations (if necessary)

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- function implementations

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Whitespace

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----------

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Tabs vs Spaces in Line Indentation: The preference in Busybox is to indent

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lines with tabs. Do not indent lines with spaces and do not indents lines

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using a mixture of tabs and spaces. (The indentation style in the Apache and

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Postfix source does this sort of thing: \s\s\s\sif (expr) {\n\tstmt; --ick.)

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The only exception to this rule is multi-line comments that use an asterisk at

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the beginning of each line, i.e.:

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/t/*

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/t * This is a block comment.

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/t * Note that it has multiple lines

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/t * and that the beginning of each line has a tab plus a space

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/t * except for the opening '/*' line where the slash

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/t * is used instead of a space.

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/t */

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Furthermore, The preference is that tabs be set to display at four spaces

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wide, but the beauty of using only tabs (and not spaces) at the beginning of

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lines is that you can set your editor to display tabs at *watever* number of

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spaces is desired and the code will still look fine.

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Operator Spacing: Put spaces between terms and operators. Example:

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Don't do this:

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for(i=0;i<num_items;i++){

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Do this instead:

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for (i = 0; i < num_items; i++) {

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While it extends the line a bit longer, the spaced version is more

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readable. An allowable exception to this rule is the situation where

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excluding the spacing makes it more obvious that we are dealing with a

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single term (even if it is a compund term) such as:

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if (str[idx] == '/' && str[idx-1] != '\\')

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or

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if ((argc-1) - (optind+1) > 0)

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Bracket Spacing: If an opening bracket starts a function, it should be on the

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next line with no spacing before it. However, if a bracet follows an opening

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control block, it should be on the same line with a single space (not a tab)

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between it and the opening control block statment. Examples:

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Don't do this:

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while (!done){

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do{

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Do this instead:

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while (!done) {

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do {

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Also, please "cuddle" your else statments by putting the else keyword on the

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same line after the right bracket that closes an 'if' statment.

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Don't do this:

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if (foo) {

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stmt;

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}

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else {

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stmt;

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}

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Do this instead:

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if (foo) {

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stmt;

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} else {

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stmt;

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}

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Paren Spacing: Put a space between C keywords and left parens, but not between

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function names and the left paren that starts it's parameter list (whether it

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is being declared or called). Examples:

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Don't do this:

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while(foo) {

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for(i = 0; i < n; i++) {

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Do this instead:

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while (foo) {

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for (i = 0; i < n; i++) {

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Do functions like this:

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static int my_func(int foo, char bar)

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...

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baz = my_func(1, 2);

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Variable and Function Names

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---------------------------

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Use the K&R style with names in all lower-case and underscores occasionally

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used to seperate words (e.g. "variable_name" and "numchars" are both

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acceptable). Using underscores makes variable and function names more readable

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because it looks like whitespace; using lower-case is easy on the eyes.

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Note: The Busybox codebase is very much a mixture of code gathered from a

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variety of locations. This explains why the current codebase contains such a

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plethora of different naming styles (Java, Pascal, K&R, just-plain-weird,

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etc.). The K&R guideline explained above should therefore be used on new files

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that are added to the repository. Furthermore, the maintainer of an existing

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file that uses alternate naming conventions should -- at his own convenience

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-- convert those names over to K&R style; converting variable names is a very

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low priority task. Perhaps in the future we will include some magical Perl

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script that can go through and convert files--left as an exersize to the

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reader.

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Tip and Pointers

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----------------

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The following are simple coding guidelines that should be followed:

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- Don't use a '#define var 80' when you can use 'static const int var 80'

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instead. This makes the compiler do typechecking for you (rather than

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relying on the more error-prone preprocessor) and it makes debugging

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programs much easier since the value of the variable can be easily queried.

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- If a const variable is used in only one function, do not make it global to

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the file. Instead, declare it inside the function body.

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- Inside applet files, all functions should be declared static so as to keep

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the global namespace clean. The only exception to this rule is the

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"applet_main" function which must be declared extern.

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- If you write a function that performs a task that could be useful outside

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the immediate file, turn it into a general-purpose function with no ties to

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any applet and put it in the utility.c file instead.

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- Put all help/usage messages in usage.c. Put other strings in messages.c

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(Side Note: we might want to use a single file instead of two, food for

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thought).

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- Do not use old-style function declarations that declare variable types

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between the parameter list and opening bracket. Example:

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Don't do this:

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int foo(parm1, parm2)

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char parm1;

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float parm2;

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{

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....

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Do this instead:

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int foo(char parm1, float parm2)

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{

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....

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- Please use brackets on all if and else statements, even if it is only one

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line. Example:

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Don't do this:

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if (foo)

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stmt;

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else

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stmt;

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Do this instead:

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if (foo) {

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stmt;

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} else {

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stmt;

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}

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The "bracketless" approach is error prone because someday you might add a

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line like this:

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if (foo)

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stmt;

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new_line();

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else

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stmt;

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And the resulting behavior of your program would totally bewilder you.

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(Don't laugh, it happens to us all.) Remember folks, this is C, not

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Python.