4 Please use the script checkpatch.pl in the scripts directory to check
5 patches before submitting.
9 Of course, the most important aspect in any coding style is whitespace.
10 Crusty old coders who have trouble spotting the glasses on their noses
11 can tell the difference between a tab and eight spaces from a distance
12 of approximately fifteen parsecs. Many a flamewar have been fought and
15 QEMU indents are four spaces. Tabs are never used, except in Makefiles
16 where they have been irreversibly coded into the syntax.
17 Spaces of course are superior to tabs because:
19 - You have just one way to specify whitespace, not two. Ambiguity breeds
21 - The confusion surrounding 'use tabs to indent, spaces to justify' is gone.
22 - Tab indents push your code to the right, making your screen seriously
24 - Tabs will be rendered incorrectly on editors who are misconfigured not
25 to use tab stops of eight positions.
26 - Tabs are rendered badly in patches, causing off-by-one errors in almost
28 - It is the QEMU coding style.
30 Do not leave whitespace dangling off the ends of lines.
34 Lines should be 80 characters; try not to make them longer.
36 Sometimes it is hard to do, especially when dealing with QEMU subsystems
37 that use long function or symbol names. Even in that case, do not make
38 lines much longer than 80 characters.
41 - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
42 xterms and use vi in all of them. The best way to punish them is to
43 let them keep doing it.
44 - Code and especially patches is much more readable if limited to a sane
45 line length. Eighty is traditional.
46 - The four-space indentation makes the most common excuse ("But look
47 at all that white space on the left!") moot.
48 - It is the QEMU coding style.
52 Variables are lower_case_with_underscores; easy to type and read. Structured
53 type names are in CamelCase; harder to type but standing out. Enum type
54 names and function type names should also be in CamelCase. Scalar type
55 names are lower_case_with_underscores_ending_with_a_t, like the POSIX
56 uint64_t and family. Note that this last convention contradicts POSIX
57 and is therefore likely to be changed.
59 When wrapping standard library functions, use the prefix qemu_ to alert
60 readers that they are seeing a wrapped version; otherwise avoid this prefix.
64 Every indented statement is braced; even if the block contains just one
65 statement. The opening brace is on the line that contains the control
66 flow statement that introduces the new block; the closing brace is on the
67 same line as the else keyword, or on a line by itself if there is no else
75 printf("a was something else entirely.\n");
78 Note that 'else if' is considered a single statement; otherwise a long if/
79 else if/else if/.../else sequence would need an indent for every else
82 An exception is the opening brace for a function; for reasons of tradition
83 and clarity it comes on a line by itself:
90 Rationale: a consistent (except for functions...) bracing style reduces
91 ambiguity and avoids needless churn when lines are added or removed.
92 Furthermore, it is the QEMU coding style.
96 Mixed declarations (interleaving statements and declarations within
97 blocks) are generally not allowed; declarations should be at the beginning
100 Every now and then, an exception is made for declarations inside a
101 #ifdef or #ifndef block: if the code looks nicer, such declarations can
102 be placed at the top of the block even if there are statements above.
103 On the other hand, however, it's often best to move that #ifdef/#ifndef
104 block to a separate function altogether.
106 6. Conditional statements
108 When comparing a variable for (in)equality with a constant, list the
109 constant on the right, as in:
112 /* Reads like: "If a equals 1" */
116 Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read.
117 Besides, good compilers already warn users when '==' is mis-typed as '=',
118 even when the constant is on the right.