wiki:Developer/Coding/80_characters_per_line

80 characters per line

Code should look good for everyone under some standard width assumptions. Where a line wraps should be the same for anyone reading the code. For historical reasons, RTEMS uses 80 characters as the maximum width for each line of code.

If you find yourself with code longer than 80 characters, first ask yourself whether the nesting level is too deep, names too long, compound expressions too complicated, or if some other guideline for improving readability can help to shrink the line length. Refactoring nested blocks into functions can help to alleviate code width problems while improving code readability. Making names descriptive yet terse can also improve readability. If absolutely necessary to have a long line, follow the rules on this page to break the line up to adhere to the 80 characters per line rule.

Breaking long lines

if, while, and for loops have their condition expressions aligned and broken on separate lines. When the conditions have to be broken, none go on the first line with the if, while, or for statement, and none go on the last line with the closing parenthesis and (optional) curly brace. Long statements are broken up and indented at operators, with an operator always being the last token on a line. No blank spaces should be left at the end of any line. Here is an example with a for loop.

for ( initialization = statement; a + really + long + statement + that + evaluates + to < a + boolean; another + statement++ ) {
  z = a + really + long + statement + that + needs + two + lines + gets + indented + four + more + spaces + on + the + second + and + subsequent + lines + and + broken + up + at + operators;
}

Should be replaced with

for (
  initialization = statement;
  a + really + long + statement + that + evaluates + to <
  a + boolean;
  another + statement++
) {
  z = a + really + long + statement + that + needs +
      two + lines + gets + indented + four + more +
      spaces + on + the + second + and + subsequent +
      lines + and + broken + up + at + operators;
}

Note that indentations should add 2 nesting levels (4 space characters, not tabs).

Similarly,

if ( this + that < those && this + these < that && this + those < these && this < those && those < that ) {

should be broken up like

if (
  this + that < those &&
  this + these < that &&
  this + those < these &&
  this < those &&
  those < that
) {

Note that each expression that resolves to a boolean goes on its own line. Where you place the boolean operator is a matter of choice.

When a line is long because of a comment at the end, move the comment to just before the line, for example

#define A_LONG_MACRO_NAME (AND + EXPANSION) /* Plus + a + really + long + comment */

can be replaced with

/* Plus + a + really + long + comment */
#define A_LONG_MACRO_NAME (AND + EXPANSION)

C Preprocessor macros need to be broken up with some care, because the preprocessor does not understand that it should eat newline characters. So

#define A_LONG_MACRO_NAME (AND + EXCESSIVELY + LONG + EXPANSION + WITH + LOTS + OF + EXTRA + STUFF + DEFINED)

would become

#define A_LONG_MACRO_NAME ( \
  AND + EXCESSIVELY + LONG + EXPANSION + WITH + LOTS + OF + EXTRA + STUFF + \
  DEFINED \
)

Notice that each line is terminated by a backslash then the carriage return. The backslash tells the preprocessor to eat the newline. Of course, if you have such a long macro, you should consider not using a macro.

Function declarations can be broken up at each argument, for example

int this_is_a_function( int arg1, int arg2, int arg3, int arg4, int arg5, int arg6, int arg7, int arg8, int arg9 );

would be broken up as

int this_is_a_function(
  int arg1,
  int arg2,
  int arg3,
  int arg4,
  int arg5,
  int arg6,
  int arg7,
  int arg8,
  int arg9
);

Excessively long comments should be broken up at a word boundary or somewhere that makes sense, for example

/* Excessively long comments should be broken up at a word boundary or somewhere that makes sense, for example */

would be

/* Excessively long comments should be broken up at a word boundary or
 * somewhere that makes sense, for example */

Note that multiline comments have a single asterisk aligned with the asterisk in the opening /*. The closing */ should go at the end of the last line.

Last modified on Jun 4, 2014 at 11:23:08 PM Last modified on Jun 4, 2014, 11:23:08 PM