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1Qemu Coding Style
2=================
3
4Please use the script checkpatch.pl in the scripts directory to check
5patches before submitting.
6
71. 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
16where they have been irreversibly coded into the syntax.
17Spaces 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
46Variables are lower_case_with_underscores; easy to type and read. Structured
47type names are in CamelCase; harder to type but standing out. Scalar type
48names are lower_case_with_underscores_ending_with_a_t, like the POSIX
49uint64_t and family. Note that this last convention contradicts POSIX
50and is therefore likely to be changed.
51
52When wrapping standard library functions, use the prefix qemu_ to alert
53readers that they are seeing a wrapped version; otherwise avoid this prefix.
54
554. Block structure
56
57Every indented statement is braced; even if the block contains just one
58statement. The opening brace is on the line that contains the control
59flow statement that introduces the new block; the closing brace is on the
60same line as the else keyword, or on a line by itself if there is no else
61keyword. Example:
62
63 if (a == 5) {
64 printf("a was 5.\n");
65 } else if (a == 6) {
66 printf("a was 6.\n");
67 } else {
68 printf("a was something else entirely.\n");
69 }
70
71An exception is the opening brace for a function; for reasons of tradition
72and clarity it comes on a line by itself:
73
74 void a_function(void)
75 {
76 do_something();
77 }
78
79Rationale: a consistent (except for functions...) bracing style reduces
80ambiguity and avoids needless churn when lines are added or removed.
81Furthermore, it is the QEMU coding style.