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Stefan Weil6576b742012-04-07 09:23:37 +02001QEMU Coding Style
aliguorie68b98d2009-04-05 17:40:34 +00002=================
3
Blue Swirlb6469682011-01-20 20:58:56 +00004Please use the script checkpatch.pl in the scripts directory to check
5patches before submitting.
6
aliguorie68b98d2009-04-05 17:40:34 +000071. Whitespace
8
9Of course, the most important aspect in any coding style is whitespace.
10Crusty old coders who have trouble spotting the glasses on their noses
11can tell the difference between a tab and eight spaces from a distance
12of approximately fifteen parsecs. Many a flamewar have been fought and
13lost on this issue.
14
15QEMU indents are four spaces. Tabs are never used, except in Makefiles
edgar_igl1cb499f2009-04-07 02:10:16 +000016where they have been irreversibly coded into the syntax.
aliguorie68b98d2009-04-05 17:40:34 +000017Spaces of course are superior to tabs because:
18
19 - You have just one way to specify whitespace, not two. Ambiguity breeds
20 mistakes.
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
23 unbalanced.
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
27 every line.
28 - It is the QEMU coding style.
29
30Do not leave whitespace dangling off the ends of lines.
31
322. Line width
33
34Lines are 80 characters; not longer.
35
36Rationale:
37 - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
38 xterms and use vi in all of them. The best way to punish them is to
39 let them keep doing it.
40 - Code and especially patches is much more readable if limited to a sane
41 line length. Eighty is traditional.
42 - It is the QEMU coding style.
43
443. Naming
45
Anthony Liguoric227f092009-10-01 16:12:16 -050046Variables are lower_case_with_underscores; easy to type and read. Structured
Peter Maydelle3c52bf2012-01-13 20:29:49 +000047type names are in CamelCase; harder to type but standing out. Enum type
48names and function type names should also be in CamelCase. Scalar type
Anthony Liguoric227f092009-10-01 16:12:16 -050049names are lower_case_with_underscores_ending_with_a_t, like the POSIX
50uint64_t and family. Note that this last convention contradicts POSIX
51and is therefore likely to be changed.
52
Avi Kivity77ac4862010-03-11 16:48:43 +020053When wrapping standard library functions, use the prefix qemu_ to alert
54readers that they are seeing a wrapped version; otherwise avoid this prefix.
55
aliguorie68b98d2009-04-05 17:40:34 +0000564. Block structure
57
58Every indented statement is braced; even if the block contains just one
59statement. The opening brace is on the line that contains the control
60flow statement that introduces the new block; the closing brace is on the
61same line as the else keyword, or on a line by itself if there is no else
62keyword. Example:
63
64 if (a == 5) {
65 printf("a was 5.\n");
66 } else if (a == 6) {
67 printf("a was 6.\n");
68 } else {
69 printf("a was something else entirely.\n");
70 }
71
Avi Kivity5f070c52011-07-25 18:55:53 +030072Note that 'else if' is considered a single statement; otherwise a long if/
73else if/else if/.../else sequence would need an indent for every else
74statement.
75
aliguorie68b98d2009-04-05 17:40:34 +000076An exception is the opening brace for a function; for reasons of tradition
77and clarity it comes on a line by itself:
78
79 void a_function(void)
80 {
81 do_something();
82 }
83
84Rationale: a consistent (except for functions...) bracing style reduces
85ambiguity and avoids needless churn when lines are added or removed.
86Furthermore, it is the QEMU coding style.