File:  [Qemu by Fabrice Bellard] / qemu / CODING_STYLE
Revision 1.1.1.4 (vendor branch): download - view: text, annotated - select for diffs
Tue Apr 24 19:18:03 2018 UTC (3 years, 1 month ago) by root
Branches: qemu, MAIN
CVS tags: qemu1001, HEAD
qemu 1.0.1

    1: Qemu Coding Style
    2: =================
    3: 
    4: Please use the script checkpatch.pl in the scripts directory to check
    5: patches before submitting.
    6: 
    7: 1. Whitespace
    8: 
    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
   13: lost on this issue.
   14: 
   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:
   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: 
   30: Do not leave whitespace dangling off the ends of lines.
   31: 
   32: 2. Line width
   33: 
   34: Lines are 80 characters; not longer.
   35: 
   36: Rationale:
   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: 
   44: 3. Naming
   45: 
   46: Variables are lower_case_with_underscores; easy to type and read.  Structured
   47: type names are in CamelCase; harder to type but standing out.  Scalar type
   48: names are lower_case_with_underscores_ending_with_a_t, like the POSIX
   49: uint64_t and family.  Note that this last convention contradicts POSIX
   50: and is therefore likely to be changed.
   51: 
   52: When wrapping standard library functions, use the prefix qemu_ to alert
   53: readers that they are seeing a wrapped version; otherwise avoid this prefix.
   54: 
   55: 4. Block structure
   56: 
   57: Every indented statement is braced; even if the block contains just one
   58: statement.  The opening brace is on the line that contains the control
   59: flow statement that introduces the new block; the closing brace is on the
   60: same line as the else keyword, or on a line by itself if there is no else
   61: keyword.  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: 
   71: Note that 'else if' is considered a single statement; otherwise a long if/
   72: else if/else if/.../else sequence would need an indent for every else
   73: statement.
   74: 
   75: An exception is the opening brace for a function; for reasons of tradition
   76: and clarity it comes on a line by itself:
   77: 
   78:     void a_function(void)
   79:     {
   80:         do_something();
   81:     }
   82: 
   83: Rationale: a consistent (except for functions...) bracing style reduces
   84: ambiguity and avoids needless churn when lines are added or removed.
   85: Furthermore, it is the QEMU coding style.

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