[821] | 1 | Busybox Style Guide
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| 2 | ===================
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| 3 |
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| 4 | This document describes the coding style conventions used in Busybox. If you
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| 5 | add a new file to Busybox or are editing an existing file, please format your
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| 6 | code according to this style. If you are the maintainer of a file that does
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| 7 | not follow these guidelines, please -- at your own convenience -- modify the
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| 8 | file(s) you maintain to bring them into conformance with this style guide.
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| 9 | Please note that this is a low priority task.
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| 10 |
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| 11 | To help you format the whitespace of your programs, an ".indent.pro" file is
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| 12 | included in the main Busybox source directory that contains option flags to
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| 13 | format code as per this style guide. This way you can run GNU indent on your
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| 14 | files by typing 'indent myfile.c myfile.h' and it will magically apply all the
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| 15 | right formatting rules to your file. Please _do_not_ run this on all the files
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| 16 | in the directory, just your own.
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| 17 |
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| 18 |
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| 19 |
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| 20 | Declaration Order
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| 21 | -----------------
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| 22 |
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[1765] | 23 | Here is the preferred order in which code should be laid out in a file:
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[821] | 24 |
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| 25 | - commented program name and one-line description
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| 26 | - commented author name and email address(es)
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| 27 | - commented GPL boilerplate
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| 28 | - commented longer description / notes for the program (if needed)
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| 29 | - #includes of .h files with angle brackets (<>) around them
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| 30 | - #includes of .h files with quotes ("") around them
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| 31 | - #defines (if any, note the section below titled "Avoid the Preprocessor")
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| 32 | - const and global variables
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| 33 | - function declarations (if necessary)
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| 34 | - function implementations
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| 35 |
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| 36 |
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| 37 |
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| 38 | Whitespace and Formatting
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| 39 | -------------------------
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| 40 |
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| 41 | This is everybody's favorite flame topic so let's get it out of the way right
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| 42 | up front.
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| 43 |
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| 44 |
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| 45 | Tabs vs. Spaces in Line Indentation
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| 46 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 47 |
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| 48 | The preference in Busybox is to indent lines with tabs. Do not indent lines
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| 49 | with spaces and do not indents lines using a mixture of tabs and spaces. (The
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| 50 | indentation style in the Apache and Postfix source does this sort of thing:
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| 51 | \s\s\s\sif (expr) {\n\tstmt; --ick.) The only exception to this rule is
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| 52 | multi-line comments that use an asterisk at the beginning of each line, i.e.:
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| 53 |
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[1765] | 54 | \t/*
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| 55 | \t * This is a block comment.
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| 56 | \t * Note that it has multiple lines
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| 57 | \t * and that the beginning of each line has a tab plus a space
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| 58 | \t * except for the opening '/*' line where the slash
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| 59 | \t * is used instead of a space.
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| 60 | \t */
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[821] | 61 |
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| 62 | Furthermore, The preference is that tabs be set to display at four spaces
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| 63 | wide, but the beauty of using only tabs (and not spaces) at the beginning of
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| 64 | lines is that you can set your editor to display tabs at *whatever* number of
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| 65 | spaces is desired and the code will still look fine.
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| 66 |
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| 67 |
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| 68 | Operator Spacing
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| 69 | ~~~~~~~~~~~~~~~~
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| 70 |
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| 71 | Put spaces between terms and operators. Example:
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| 72 |
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| 73 | Don't do this:
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| 74 |
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| 75 | for(i=0;i<num_items;i++){
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| 76 |
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| 77 | Do this instead:
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| 78 |
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| 79 | for (i = 0; i < num_items; i++) {
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| 80 |
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| 81 | While it extends the line a bit longer, the spaced version is more
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| 82 | readable. An allowable exception to this rule is the situation where
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| 83 | excluding the spacing makes it more obvious that we are dealing with a
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| 84 | single term (even if it is a compound term) such as:
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| 85 |
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| 86 | if (str[idx] == '/' && str[idx-1] != '\\')
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| 87 |
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| 88 | or
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| 89 |
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| 90 | if ((argc-1) - (optind+1) > 0)
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| 91 |
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| 92 |
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| 93 | Bracket Spacing
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| 94 | ~~~~~~~~~~~~~~~
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| 95 |
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| 96 | If an opening bracket starts a function, it should be on the
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| 97 | next line with no spacing before it. However, if a bracket follows an opening
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| 98 | control block, it should be on the same line with a single space (not a tab)
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| 99 | between it and the opening control block statement. Examples:
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| 100 |
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| 101 | Don't do this:
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| 102 |
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| 103 | while (!done)
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| 104 | {
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| 105 |
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| 106 | do
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| 107 | {
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| 108 |
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| 109 | Don't do this either:
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| 110 |
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| 111 | while (!done){
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| 112 |
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| 113 | do{
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| 114 |
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| 115 | And for heaven's sake, don't do this:
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| 116 |
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| 117 | while (!done)
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| 118 | {
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| 119 |
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| 120 | do
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| 121 | {
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| 122 |
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| 123 | Do this instead:
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| 124 |
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| 125 | while (!done) {
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| 126 |
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| 127 | do {
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| 128 |
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[1765] | 129 | If you have long logic statements that need to be wrapped, then uncuddling
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| 130 | the bracket to improve readability is allowed. Generally, this style makes
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| 131 | it easier for reader to notice that 2nd and following lines are still
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| 132 | inside 'if':
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[821] | 133 |
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[1765] | 134 | if (some_really_long_checks && some_other_really_long_checks
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| 135 | && some_more_really_long_checks
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| 136 | && even_more_of_long_checks
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| 137 | ) {
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[821] | 138 | do_foo_now;
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| 139 |
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| 140 | Spacing around Parentheses
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| 141 | ~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 142 |
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| 143 | Put a space between C keywords and left parens, but not between function names
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| 144 | and the left paren that starts it's parameter list (whether it is being
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| 145 | declared or called). Examples:
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| 146 |
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| 147 | Don't do this:
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| 148 |
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| 149 | while(foo) {
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| 150 | for(i = 0; i < n; i++) {
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| 151 |
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| 152 | Do this instead:
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| 153 |
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| 154 | while (foo) {
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| 155 | for (i = 0; i < n; i++) {
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| 156 |
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| 157 | But do functions like this:
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| 158 |
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| 159 | static int my_func(int foo, char bar)
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| 160 | ...
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| 161 | baz = my_func(1, 2);
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| 162 |
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| 163 | Also, don't put a space between the left paren and the first term, nor between
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| 164 | the last arg and the right paren.
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| 165 |
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| 166 | Don't do this:
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| 167 |
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| 168 | if ( x < 1 )
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| 169 | strcmp( thisstr, thatstr )
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| 170 |
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| 171 | Do this instead:
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| 172 |
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| 173 | if (x < 1)
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| 174 | strcmp(thisstr, thatstr)
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| 175 |
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| 176 |
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| 177 | Cuddled Elses
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| 178 | ~~~~~~~~~~~~~
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| 179 |
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| 180 | Also, please "cuddle" your else statements by putting the else keyword on the
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| 181 | same line after the right bracket that closes an 'if' statement.
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| 182 |
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| 183 | Don't do this:
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| 184 |
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| 185 | if (foo) {
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| 186 | stmt;
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| 187 | }
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| 188 | else {
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| 189 | stmt;
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| 190 | }
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| 191 |
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| 192 | Do this instead:
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| 193 |
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| 194 | if (foo) {
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| 195 | stmt;
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| 196 | } else {
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| 197 | stmt;
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| 198 | }
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| 199 |
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| 200 | The exception to this rule is if you want to include a comment before the else
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| 201 | block. Example:
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| 202 |
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| 203 | if (foo) {
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| 204 | stmts...
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| 205 | }
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| 206 | /* otherwise, we're just kidding ourselves, so re-frob the input */
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| 207 | else {
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| 208 | other_stmts...
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| 209 | }
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| 210 |
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| 211 |
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[1765] | 212 | Labels
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| 213 | ~~~~~~
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[821] | 214 |
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[1765] | 215 | Labels should start at the beginning of the line, not indented to the block
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| 216 | level (because they do not "belong" to block scope, only to whole function).
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| 217 |
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| 218 | if (foo) {
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| 219 | stmt;
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| 220 | label:
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| 221 | stmt2;
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| 222 | stmt;
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| 223 | }
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| 224 |
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| 225 | (Putting label at position 1 prevents diff -p from confusing label for function
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| 226 | name, but it's not a policy of busybox project to enforce such a minor detail).
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| 227 |
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| 228 |
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| 229 |
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[821] | 230 | Variable and Function Names
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| 231 | ---------------------------
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| 232 |
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| 233 | Use the K&R style with names in all lower-case and underscores occasionally
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| 234 | used to separate words (e.g., "variable_name" and "numchars" are both
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| 235 | acceptable). Using underscores makes variable and function names more readable
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| 236 | because it looks like whitespace; using lower-case is easy on the eyes.
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| 237 |
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| 238 | Frowned upon:
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| 239 |
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| 240 | hitList
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| 241 | TotalChars
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| 242 | szFileName
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| 243 | pf_Nfol_TriState
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| 244 |
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| 245 | Preferred:
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| 246 |
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| 247 | hit_list
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| 248 | total_chars
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| 249 | file_name
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| 250 | sensible_name
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| 251 |
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| 252 | Exceptions:
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| 253 |
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| 254 | - Enums, macros, and constant variables are occasionally written in all
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[1765] | 255 | upper-case with words optionally seperatedy by underscores (i.e. FIFO_TYPE,
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[821] | 256 | ISBLKDEV()).
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| 257 |
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| 258 | - Nobody is going to get mad at you for using 'pvar' as the name of a
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| 259 | variable that is a pointer to 'var'.
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| 260 |
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| 261 |
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| 262 | Converting to K&R
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| 263 | ~~~~~~~~~~~~~~~~~
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| 264 |
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| 265 | The Busybox codebase is very much a mixture of code gathered from a variety of
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| 266 | sources. This explains why the current codebase contains such a hodge-podge of
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| 267 | different naming styles (Java, Pascal, K&R, just-plain-weird, etc.). The K&R
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| 268 | guideline explained above should therefore be used on new files that are added
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| 269 | to the repository. Furthermore, the maintainer of an existing file that uses
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| 270 | alternate naming conventions should, at his own convenience, convert those
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| 271 | names over to K&R style. Converting variable names is a very low priority
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| 272 | task.
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| 273 |
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| 274 | If you want to do a search-and-replace of a single variable name in different
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| 275 | files, you can do the following in the busybox directory:
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| 276 |
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| 277 | $ perl -pi -e 's/\bOldVar\b/new_var/g' *.[ch]
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| 278 |
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| 279 | If you want to convert all the non-K&R vars in your file all at once, follow
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| 280 | these steps:
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| 281 |
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| 282 | - In the busybox directory type 'examples/mk2knr.pl files-to-convert'. This
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| 283 | does not do the actual conversion, rather, it generates a script called
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| 284 | 'convertme.pl' that shows what will be converted, giving you a chance to
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| 285 | review the changes beforehand.
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| 286 |
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| 287 | - Review the 'convertme.pl' script that gets generated in the busybox
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| 288 | directory and remove / edit any of the substitutions in there. Please
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| 289 | especially check for false positives (strings that should not be
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| 290 | converted).
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| 291 |
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| 292 | - Type './convertme.pl same-files-as-before' to perform the actual
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| 293 | conversion.
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| 294 |
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| 295 | - Compile and see if everything still works.
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| 296 |
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| 297 | Please be aware of changes that have cascading effects into other files. For
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| 298 | example, if you're changing the name of something in, say utility.c, you
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| 299 | should probably run 'examples/mk2knr.pl utility.c' at first, but when you run
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| 300 | the 'convertme.pl' script you should run it on _all_ files like so:
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| 301 | './convertme.pl *.[ch]'.
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| 302 |
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| 303 |
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| 304 |
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| 305 | Avoid The Preprocessor
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| 306 | ----------------------
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| 307 |
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| 308 | At best, the preprocessor is a necessary evil, helping us account for platform
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| 309 | and architecture differences. Using the preprocessor unnecessarily is just
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| 310 | plain evil.
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| 311 |
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| 312 |
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| 313 | The Folly of #define
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| 314 | ~~~~~~~~~~~~~~~~~~~~
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| 315 |
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| 316 | Use 'const <type> var' for declaring constants.
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| 317 |
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| 318 | Don't do this:
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| 319 |
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[1765] | 320 | #define CONST 80
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[821] | 321 |
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| 322 | Do this instead, when the variable is in a header file and will be used in
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| 323 | several source files:
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| 324 |
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[1765] | 325 | enum { CONST = 80 };
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[821] | 326 |
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[1765] | 327 | Although enum may look ugly to some people, it is better for code size.
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| 328 | With "const int" compiler may fail to optimize it out and will reserve
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| 329 | a real storage in rodata for it! (Hopefully, newer gcc will get better
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| 330 | at it...). With "define", you have slight risk of polluting namespace
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| 331 | (#define doesn't allow you to redefine the name in the inner scopes),
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| 332 | and complex "define" are evaluated each time they uesd, not once
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| 333 | at declarations like enums. Also, the preprocessor does _no_ type checking
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| 334 | whatsoever, making it much more error prone.
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[821] | 335 |
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| 336 |
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| 337 | The Folly of Macros
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| 338 | ~~~~~~~~~~~~~~~~~~~
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| 339 |
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| 340 | Use 'static inline' instead of a macro.
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| 341 |
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| 342 | Don't do this:
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| 343 |
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| 344 | #define mini_func(param1, param2) (param1 << param2)
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| 345 |
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| 346 | Do this instead:
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| 347 |
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| 348 | static inline int mini_func(int param1, param2)
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| 349 | {
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| 350 | return (param1 << param2);
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| 351 | }
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| 352 |
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| 353 | Static inline functions are greatly preferred over macros. They provide type
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| 354 | safety, have no length limitations, no formatting limitations, have an actual
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| 355 | return value, and under gcc they are as cheap as macros. Besides, really long
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| 356 | macros with backslashes at the end of each line are ugly as sin.
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| 357 |
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| 358 |
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| 359 | The Folly of #ifdef
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| 360 | ~~~~~~~~~~~~~~~~~~~
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| 361 |
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| 362 | Code cluttered with ifdefs is difficult to read and maintain. Don't do it.
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| 363 | Instead, put your ifdefs at the top of your .c file (or in a header), and
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| 364 | conditionally define 'static inline' functions, (or *maybe* macros), which are
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| 365 | used in the code.
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| 366 |
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| 367 | Don't do this:
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| 368 |
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| 369 | ret = my_func(bar, baz);
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| 370 | if (!ret)
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| 371 | return -1;
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| 372 | #ifdef CONFIG_FEATURE_FUNKY
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| 373 | maybe_do_funky_stuff(bar, baz);
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| 374 | #endif
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| 375 |
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| 376 | Do this instead:
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| 377 |
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| 378 | (in .h header file)
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| 379 |
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[1765] | 380 | #if ENABLE_FEATURE_FUNKY
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| 381 | static inline void maybe_do_funky_stuff(int bar, int baz)
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[821] | 382 | {
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| 383 | /* lotsa code in here */
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| 384 | }
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| 385 | #else
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[1765] | 386 | static inline void maybe_do_funky_stuff(int bar, int baz) {}
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[821] | 387 | #endif
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| 388 |
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| 389 | (in the .c source file)
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| 390 |
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| 391 | ret = my_func(bar, baz);
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| 392 | if (!ret)
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| 393 | return -1;
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| 394 | maybe_do_funky_stuff(bar, baz);
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| 395 |
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| 396 | The great thing about this approach is that the compiler will optimize away
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| 397 | the "no-op" case (the empty function) when the feature is turned off.
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| 398 |
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| 399 | Note also the use of the word 'maybe' in the function name to indicate
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| 400 | conditional execution.
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| 401 |
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| 402 |
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| 403 |
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| 404 | Notes on Strings
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| 405 | ----------------
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| 406 |
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| 407 | Strings in C can get a little thorny. Here's some guidelines for dealing with
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| 408 | strings in Busybox. (There is surely more that could be added to this
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| 409 | section.)
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| 410 |
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| 411 |
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| 412 | String Files
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| 413 | ~~~~~~~~~~~~
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| 414 |
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| 415 | Put all help/usage messages in usage.c. Put other strings in messages.c.
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| 416 | Putting these strings into their own file is a calculated decision designed to
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| 417 | confine spelling errors to a single place and aid internationalization
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| 418 | efforts, if needed. (Side Note: we might want to use a single file - maybe
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| 419 | called 'strings.c' - instead of two, food for thought).
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| 420 |
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| 421 |
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| 422 | Testing String Equivalence
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| 423 | ~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 424 |
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| 425 | There's a right way and a wrong way to test for sting equivalence with
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| 426 | strcmp():
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| 427 |
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| 428 | The wrong way:
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| 429 |
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| 430 | if (!strcmp(string, "foo")) {
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| 431 | ...
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| 432 |
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| 433 | The right way:
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| 434 |
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| 435 | if (strcmp(string, "foo") == 0){
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| 436 | ...
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| 437 |
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| 438 | The use of the "equals" (==) operator in the latter example makes it much more
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| 439 | obvious that you are testing for equivalence. The former example with the
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| 440 | "not" (!) operator makes it look like you are testing for an error. In a more
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| 441 | perfect world, we would have a streq() function in the string library, but
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| 442 | that ain't the world we're living in.
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| 443 |
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| 444 |
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| 445 | Avoid Dangerous String Functions
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| 446 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 447 |
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| 448 | Unfortunately, the way C handles strings makes them prone to overruns when
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| 449 | certain library functions are (mis)used. The following table offers a summary
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| 450 | of some of the more notorious troublemakers:
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| 451 |
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[1765] | 452 | function overflows preferred
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| 453 | -------------------------------------------------
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| 454 | strcpy dest string safe_strncpy
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| 455 | strncpy may fail to 0-terminate dst safe_strncpy
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| 456 | strcat dest string strncat
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| 457 | gets string it gets fgets
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| 458 | getwd buf string getcwd
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| 459 | [v]sprintf str buffer [v]snprintf
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| 460 | realpath path buffer use with pathconf
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| 461 | [vf]scanf its arguments just avoid it
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[821] | 462 |
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| 463 |
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| 464 | The above is by no means a complete list. Be careful out there.
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| 465 |
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| 466 |
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| 467 |
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| 468 | Avoid Big Static Buffers
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| 469 | ------------------------
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| 470 |
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[1765] | 471 | First, some background to put this discussion in context: static buffers look
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[821] | 472 | like this in code:
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| 473 |
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| 474 | /* in a .c file outside any functions */
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| 475 | static char buffer[BUFSIZ]; /* happily used by any function in this file,
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| 476 | but ick! big! */
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| 477 |
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| 478 | The problem with these is that any time any busybox app is run, you pay a
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| 479 | memory penalty for this buffer, even if the applet that uses said buffer is
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| 480 | not run. This can be fixed, thusly:
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| 481 |
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| 482 | static char *buffer;
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| 483 | ...
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| 484 | other_func()
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| 485 | {
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| 486 | strcpy(buffer, lotsa_chars); /* happily uses global *buffer */
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| 487 | ...
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| 488 | foo_main()
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| 489 | {
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| 490 | buffer = xmalloc(sizeof(char)*BUFSIZ);
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| 491 | ...
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| 492 |
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| 493 | However, this approach trades bss segment for text segment. Rather than
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| 494 | mallocing the buffers (and thus growing the text size), buffers can be
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| 495 | declared on the stack in the *_main() function and made available globally by
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| 496 | assigning them to a global pointer thusly:
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| 497 |
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| 498 | static char *pbuffer;
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| 499 | ...
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| 500 | other_func()
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| 501 | {
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| 502 | strcpy(pbuffer, lotsa_chars); /* happily uses global *pbuffer */
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| 503 | ...
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| 504 | foo_main()
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| 505 | {
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| 506 | char *buffer[BUFSIZ]; /* declared locally, on stack */
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| 507 | pbuffer = buffer; /* but available globally */
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| 508 | ...
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| 509 |
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| 510 | This last approach has some advantages (low code size, space not used until
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| 511 | it's needed), but can be a problem in some low resource machines that have
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| 512 | very limited stack space (e.g., uCLinux).
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| 513 |
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| 514 | A macro is declared in busybox.h that implements compile-time selection
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| 515 | between xmalloc() and stack creation, so you can code the line in question as
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| 516 |
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| 517 | RESERVE_CONFIG_BUFFER(buffer, BUFSIZ);
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| 518 |
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| 519 | and the right thing will happen, based on your configuration.
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| 520 |
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[1765] | 521 | Another relatively new trick of similar nature is explained
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| 522 | in keep_data_small.txt.
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[821] | 523 |
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| 524 |
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[1765] | 525 |
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[821] | 526 | Miscellaneous Coding Guidelines
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| 527 | -------------------------------
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| 528 |
|
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| 529 | The following are important items that don't fit into any of the above
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| 530 | sections.
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| 531 |
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| 532 |
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| 533 | Model Busybox Applets After GNU Counterparts
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| 534 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 535 |
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| 536 | When in doubt about the proper behavior of a Busybox program (output,
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| 537 | formatting, options, etc.), model it after the equivalent GNU program.
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| 538 | Doesn't matter how that program behaves on some other flavor of *NIX; doesn't
|
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| 539 | matter what the POSIX standard says or doesn't say, just model Busybox
|
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| 540 | programs after their GNU counterparts and it will make life easier on (nearly)
|
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| 541 | everyone.
|
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| 542 |
|
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| 543 | The only time we deviate from emulating the GNU behavior is when:
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| 544 |
|
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| 545 | - We are deliberately not supporting a feature (such as a command line
|
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| 546 | switch)
|
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| 547 | - Emulating the GNU behavior is prohibitively expensive (lots more code
|
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| 548 | would be required, lots more memory would be used, etc.)
|
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| 549 | - The difference is minor or cosmetic
|
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| 550 |
|
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[1765] | 551 | A note on the 'cosmetic' case: output differences might be considered
|
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[821] | 552 | cosmetic, but if the output is significant enough to break other scripts that
|
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| 553 | use the output, it should really be fixed.
|
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| 554 |
|
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| 555 |
|
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| 556 | Scope
|
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| 557 | ~~~~~
|
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| 558 |
|
---|
| 559 | If a const variable is used only in a single source file, put it in the source
|
---|
| 560 | file and not in a header file. Likewise, if a const variable is used in only
|
---|
| 561 | one function, do not make it global to the file. Instead, declare it inside
|
---|
| 562 | the function body. Bottom line: Make a conscious effort to limit declarations
|
---|
| 563 | to the smallest scope possible.
|
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| 564 |
|
---|
| 565 | Inside applet files, all functions should be declared static so as to keep the
|
---|
| 566 | global name space clean. The only exception to this rule is the "applet_main"
|
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| 567 | function which must be declared extern.
|
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| 568 |
|
---|
| 569 | If you write a function that performs a task that could be useful outside the
|
---|
| 570 | immediate file, turn it into a general-purpose function with no ties to any
|
---|
| 571 | applet and put it in the utility.c file instead.
|
---|
| 572 |
|
---|
| 573 |
|
---|
| 574 | Brackets Are Your Friends
|
---|
| 575 | ~~~~~~~~~~~~~~~~~~~~~~~~~
|
---|
| 576 |
|
---|
| 577 | Please use brackets on all if and else statements, even if it is only one
|
---|
| 578 | line. Example:
|
---|
| 579 |
|
---|
| 580 | Don't do this:
|
---|
| 581 |
|
---|
| 582 | if (foo)
|
---|
| 583 | stmt1;
|
---|
| 584 | stmt2
|
---|
| 585 | stmt3;
|
---|
| 586 |
|
---|
| 587 | Do this instead:
|
---|
| 588 |
|
---|
| 589 | if (foo) {
|
---|
| 590 | stmt1;
|
---|
| 591 | }
|
---|
| 592 | stmt2
|
---|
| 593 | stmt3;
|
---|
| 594 |
|
---|
| 595 | The "bracketless" approach is error prone because someday you might add a line
|
---|
| 596 | like this:
|
---|
| 597 |
|
---|
| 598 | if (foo)
|
---|
| 599 | stmt1;
|
---|
| 600 | new_line();
|
---|
[1765] | 601 | stmt2;
|
---|
[821] | 602 | stmt3;
|
---|
| 603 |
|
---|
| 604 | And the resulting behavior of your program would totally bewilder you. (Don't
|
---|
| 605 | laugh, it happens to us all.) Remember folks, this is C, not Python.
|
---|
| 606 |
|
---|
| 607 |
|
---|
| 608 | Function Declarations
|
---|
| 609 | ~~~~~~~~~~~~~~~~~~~~~
|
---|
| 610 |
|
---|
| 611 | Do not use old-style function declarations that declare variable types between
|
---|
| 612 | the parameter list and opening bracket. Example:
|
---|
| 613 |
|
---|
| 614 | Don't do this:
|
---|
| 615 |
|
---|
| 616 | int foo(parm1, parm2)
|
---|
| 617 | char parm1;
|
---|
| 618 | float parm2;
|
---|
| 619 | {
|
---|
| 620 | ....
|
---|
| 621 |
|
---|
| 622 | Do this instead:
|
---|
| 623 |
|
---|
| 624 | int foo(char parm1, float parm2)
|
---|
| 625 | {
|
---|
| 626 | ....
|
---|
| 627 |
|
---|
| 628 | The only time you would ever need to use the old declaration syntax is to
|
---|
| 629 | support ancient, antediluvian compilers. To our good fortune, we have access
|
---|
| 630 | to more modern compilers and the old declaration syntax is neither necessary
|
---|
| 631 | nor desired.
|
---|
| 632 |
|
---|
| 633 |
|
---|
| 634 | Emphasizing Logical Blocks
|
---|
| 635 | ~~~~~~~~~~~~~~~~~~~~~~~~~~
|
---|
| 636 |
|
---|
| 637 | Organization and readability are improved by putting extra newlines around
|
---|
| 638 | blocks of code that perform a single task. These are typically blocks that
|
---|
| 639 | begin with a C keyword, but not always.
|
---|
| 640 |
|
---|
| 641 | Furthermore, you should put a single comment (not necessarily one line, just
|
---|
| 642 | one comment) before the block, rather than commenting each and every line.
|
---|
[1765] | 643 | There is an optimal amount of commenting that a program can have; you can
|
---|
[821] | 644 | comment too much as well as too little.
|
---|
| 645 |
|
---|
| 646 | A picture is really worth a thousand words here, the following example
|
---|
| 647 | illustrates how to emphasize logical blocks:
|
---|
| 648 |
|
---|
[1765] | 649 | while (line = xmalloc_fgets(fp)) {
|
---|
[821] | 650 |
|
---|
| 651 | /* eat the newline, if any */
|
---|
| 652 | chomp(line);
|
---|
| 653 |
|
---|
| 654 | /* ignore blank lines */
|
---|
| 655 | if (strlen(file_to_act_on) == 0) {
|
---|
| 656 | continue;
|
---|
| 657 | }
|
---|
| 658 |
|
---|
| 659 | /* if the search string is in this line, print it,
|
---|
| 660 | * unless we were told to be quiet */
|
---|
| 661 | if (strstr(line, search) && !be_quiet) {
|
---|
| 662 | puts(line);
|
---|
| 663 | }
|
---|
| 664 |
|
---|
| 665 | /* clean up */
|
---|
| 666 | free(line);
|
---|
| 667 | }
|
---|
| 668 |
|
---|
| 669 |
|
---|
| 670 | Processing Options with getopt
|
---|
| 671 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
---|
| 672 |
|
---|
[1765] | 673 | If your applet needs to process command-line switches, please use getopt32() to
|
---|
[821] | 674 | do so. Numerous examples can be seen in many of the existing applets, but
|
---|
| 675 | basically it boils down to two things: at the top of the .c file, have this
|
---|
[1765] | 676 | line in the midst of your #includes, if you need to parse long options:
|
---|
[821] | 677 |
|
---|
| 678 | #include <getopt.h>
|
---|
| 679 |
|
---|
[1765] | 680 | Then have long options defined:
|
---|
| 681 |
|
---|
| 682 | static const struct option <applet>_long_options[] = {
|
---|
| 683 | { "list", 0, NULL, 't' },
|
---|
| 684 | { "extract", 0, NULL, 'x' },
|
---|
| 685 | { NULL, 0, NULL, 0 }
|
---|
| 686 | };
|
---|
| 687 |
|
---|
[821] | 688 | And a code block similar to the following near the top of your applet_main()
|
---|
| 689 | routine:
|
---|
| 690 |
|
---|
[1765] | 691 | char *str_b;
|
---|
[821] | 692 |
|
---|
[1765] | 693 | opt_complementary = "cryptic_string";
|
---|
| 694 | applet_long_options = <applet>_long_options; /* if you have them */
|
---|
| 695 | opt = getopt32(argc, argv, "ab:c", &str_b);
|
---|
| 696 | if (opt & 1) {
|
---|
| 697 | handle_option_a();
|
---|
| 698 | }
|
---|
| 699 | if (opt & 2) {
|
---|
| 700 | handle_option_b(str_b);
|
---|
| 701 | }
|
---|
| 702 | if (opt & 4) {
|
---|
| 703 | handle_option_c();
|
---|
| 704 | }
|
---|
| 705 |
|
---|
[821] | 706 | If your applet takes no options (such as 'init'), there should be a line
|
---|
| 707 | somewhere in the file reads:
|
---|
| 708 |
|
---|
| 709 | /* no options, no getopt */
|
---|
| 710 |
|
---|
| 711 | That way, when people go grepping to see which applets need to be converted to
|
---|
| 712 | use getopt, they won't get false positives.
|
---|
| 713 |
|
---|
[1765] | 714 | For more info and examples, examine getopt32.c, tar.c, wget.c etc.
|
---|