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authoraliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>2009-04-05 17:40:34 +0000
committeraliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>2009-04-05 17:40:34 +0000
commite68b98dc7237d76fdef5c5d403d0613b443102da (patch)
tree0f8cab3b76be8068e940268cbc5f1e45c2a5236d /CODING_STYLE
parent8eca6b1bc770982595db2f7207c65051572436cb (diff)
Document QEMU coding style (v2) (Avi Kivity)
With the help of some Limoncino I noted several aspects of the QEMU coding style, particularly where it differs from the Linux coding style as many contributors work on both projects. Signed-off-by: Avi Kivity <avi@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6976 c046a42c-6fe2-441c-8c8c-71466251a162
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+Qemu Coding Style
+=================
+
+1. Whitespace
+
+Of course, the most important aspect in any coding style is whitespace.
+Crusty old coders who have trouble spotting the glasses on their noses
+can tell the difference between a tab and eight spaces from a distance
+of approximately fifteen parsecs. Many a flamewar have been fought and
+lost on this issue.
+
+QEMU indents are four spaces. Tabs are never used, except in Makefiles
+where they have been irreversibly coded into the syntax by some moron.
+Spaces of course are superior to tabs because:
+
+ - You have just one way to specify whitespace, not two. Ambiguity breeds
+ mistakes.
+ - The confusion surrounding 'use tabs to indent, spaces to justify' is gone.
+ - Tab indents push your code to the right, making your screen seriously
+ unbalanced.
+ - Tabs will be rendered incorrectly on editors who are misconfigured not
+ to use tab stops of eight positions.
+ - Tabs are rendered badly in patches, causing off-by-one errors in almost
+ every line.
+ - It is the QEMU coding style.
+
+Do not leave whitespace dangling off the ends of lines.
+
+2. Line width
+
+Lines are 80 characters; not longer.
+
+Rationale:
+ - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
+ xterms and use vi in all of them. The best way to punish them is to
+ let them keep doing it.
+ - Code and especially patches is much more readable if limited to a sane
+ line length. Eighty is traditional.
+ - It is the QEMU coding style.
+
+3. Naming
+
+Variables are lower_case_with_underscores; easy to type and read. Structured
+type names are in CamelCase; harder to type but standing out. Scalar type
+names are lower_case_with_underscores_ending_with_a_t, like the POSIX
+uint64_t and family. Note that this last convention contradicts POSIX
+and is therefore likely to be changed.
+
+Typedefs are used to eliminate the redundant 'struct' keyword. It is the
+QEMU coding style.
+
+4. Block structure
+
+Every indented statement is braced; even if the block contains just one
+statement. The opening brace is on the line that contains the control
+flow statement that introduces the new block; the closing brace is on the
+same line as the else keyword, or on a line by itself if there is no else
+keyword. Example:
+
+ if (a == 5) {
+ printf("a was 5.\n");
+ } else if (a == 6) {
+ printf("a was 6.\n");
+ } else {
+ printf("a was something else entirely.\n");
+ }
+
+An exception is the opening brace for a function; for reasons of tradition
+and clarity it comes on a line by itself:
+
+ void a_function(void)
+ {
+ do_something();
+ }
+
+Rationale: a consistent (except for functions...) bracing style reduces
+ambiguity and avoids needless churn when lines are added or removed.
+Furthermore, it is the QEMU coding style.