File:  [Qemu by Fabrice Bellard] / qemu / CODING_STYLE
Revision 1.1.1.1 (vendor branch): download - view: text, annotated - select for diffs
Tue Apr 24 17:21:30 2018 UTC (3 years, 3 months ago) by root
Branches: qemu, MAIN
CVS tags: qemu0125, qemu0124, qemu0123, qemu0122, qemu0121, qemu0120, qemu0111, qemu0110, HEAD
qemu 0.11.0

    1: Qemu Coding Style
    2: =================
    3: 
    4: 1. Whitespace
    5: 
    6: Of course, the most important aspect in any coding style is whitespace.
    7: Crusty old coders who have trouble spotting the glasses on their noses
    8: can tell the difference between a tab and eight spaces from a distance
    9: of approximately fifteen parsecs.  Many a flamewar have been fought and
   10: lost on this issue.
   11: 
   12: QEMU indents are four spaces.  Tabs are never used, except in Makefiles
   13: where they have been irreversibly coded into the syntax.
   14: Spaces of course are superior to tabs because:
   15: 
   16:  - You have just one way to specify whitespace, not two.  Ambiguity breeds
   17:    mistakes.
   18:  - The confusion surrounding 'use tabs to indent, spaces to justify' is gone.
   19:  - Tab indents push your code to the right, making your screen seriously
   20:    unbalanced.
   21:  - Tabs will be rendered incorrectly on editors who are misconfigured not
   22:    to use tab stops of eight positions.
   23:  - Tabs are rendered badly in patches, causing off-by-one errors in almost
   24:    every line.
   25:  - It is the QEMU coding style.
   26: 
   27: Do not leave whitespace dangling off the ends of lines.
   28: 
   29: 2. Line width
   30: 
   31: Lines are 80 characters; not longer.
   32: 
   33: Rationale:
   34:  - Some people like to tile their 24" screens with a 6x4 matrix of 80x24
   35:    xterms and use vi in all of them.  The best way to punish them is to
   36:    let them keep doing it.
   37:  - Code and especially patches is much more readable if limited to a sane
   38:    line length.  Eighty is traditional.
   39:  - It is the QEMU coding style.
   40: 
   41: 3. Naming
   42: 
   43: Variables are lower_case_with_underscores; easy to type and read.  Structured
   44: type names are in CamelCase; harder to type but standing out.  Scalar type
   45: names are lower_case_with_underscores_ending_with_a_t, like the POSIX
   46: uint64_t and family.  Note that this last convention contradicts POSIX
   47: and is therefore likely to be changed.
   48: 
   49: Typedefs are used to eliminate the redundant 'struct' keyword.  It is the
   50: QEMU coding style.
   51: 
   52: 4. Block structure
   53: 
   54: Every indented statement is braced; even if the block contains just one
   55: statement.  The opening brace is on the line that contains the control
   56: flow statement that introduces the new block; the closing brace is on the
   57: same line as the else keyword, or on a line by itself if there is no else
   58: keyword.  Example:
   59: 
   60:     if (a == 5) {
   61:         printf("a was 5.\n");
   62:     } else if (a == 6) {
   63:         printf("a was 6.\n");
   64:     } else {
   65:         printf("a was something else entirely.\n");
   66:     }
   67: 
   68: An exception is the opening brace for a function; for reasons of tradition
   69: and clarity it comes on a line by itself:
   70: 
   71:     void a_function(void)
   72:     {
   73:         do_something();
   74:     }
   75: 
   76: Rationale: a consistent (except for functions...) bracing style reduces
   77: ambiguity and avoids needless churn when lines are added or removed.
   78: Furthermore, it is the QEMU coding style.

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