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Annotation of qemu/CODING_STYLE, revision 1.1.1.5

1.1.1.5 ! root        1: QEMU Coding Style
1.1       root        2: =================
                      3: 
1.1.1.3   root        4: Please use the script checkpatch.pl in the scripts directory to check
                      5: patches before submitting.
                      6: 
1.1       root        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
1.1.1.5 ! root       47: type names are in CamelCase; harder to type but standing out.  Enum type
        !            48: names and function type names should also be in CamelCase.  Scalar type
1.1       root       49: names are lower_case_with_underscores_ending_with_a_t, like the POSIX
                     50: uint64_t and family.  Note that this last convention contradicts POSIX
                     51: and is therefore likely to be changed.
                     52: 
1.1.1.2   root       53: When wrapping standard library functions, use the prefix qemu_ to alert
                     54: readers that they are seeing a wrapped version; otherwise avoid this prefix.
                     55: 
1.1       root       56: 4. Block structure
                     57: 
                     58: Every indented statement is braced; even if the block contains just one
                     59: statement.  The opening brace is on the line that contains the control
                     60: flow statement that introduces the new block; the closing brace is on the
                     61: same line as the else keyword, or on a line by itself if there is no else
                     62: keyword.  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: 
1.1.1.4   root       72: Note that 'else if' is considered a single statement; otherwise a long if/
                     73: else if/else if/.../else sequence would need an indent for every else
                     74: statement.
                     75: 
1.1       root       76: An exception is the opening brace for a function; for reasons of tradition
                     77: and clarity it comes on a line by itself:
                     78: 
                     79:     void a_function(void)
                     80:     {
                     81:         do_something();
                     82:     }
                     83: 
                     84: Rationale: a consistent (except for functions...) bracing style reduces
                     85: ambiguity and avoids needless churn when lines are added or removed.
                     86: Furthermore, it is the QEMU coding style.

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