4. Names

name length

Names should be unique in their first 31 characters. Don't bother with 6-character uniqueness as required for strict C89 compliance.

macros

Macros without parameters and function-like macros that evaluate their arguments multiple times or that have unsafe side effects should have names in all capitals (including the prefix). Well-behaved function-like macros should have their names in lowercase.

Macro parameters should have all-uppercase names.

number

Prefer singular nouns to plural in names. In particular, arrays should have singular names.

qualifiers

Qualifiers such as ttl, sum, avg, min, max, ... go at the end of names following an underscore. (See the table of abbreviations below.)

Do not use num as a qualifier, since it can mean "number of the current item" or "number of items". Use cur or idx for the former meaning, cnt for the latter.

keywords in other languages

When writing a parser, compiler, etc., for a language, write that language's reserved words in all capitals in names; e.g., parse_DATA_LIST() as a function to parse a PSPP DATA LIST construct. Do not use such a capitalized keyword as the only component of a name.

status variables

Name status variables and Boolean variables for their meaning: done, error, found, success, .... There is an implied, unwritten "is": (is_)done, etc.

negative names

Avoid negative names such as not_found.

numbers in names

Names that contain digits should usually be restricted to ranges. Use 0 and 1 for range endpoints, not 1 and 2: x0 and x1.

size versus length

A size is a count of bytes, a length is a count of characters. A buffer has size, but a string has length. The length of a string does not include the null terminator, but the size of the buffer that contains the string does.

reserved names

Avoid names reserved by ANSI C89 and C99 and by POSIX.

p-convention

A _p suffix indicates a boolean test for the condition described by the rest of the name. (This comes from Lisp.)

abbreviations

Consistently use the following standard abbreviations for English words in C names:

amount	amt
average	avg
buffer	buf
calculate	calc
command	cmd
compare	cmp
count	cnt
current	cur
decrement	dec
destination	dst
enumeration	enum
expression	expr
function	func
increment	inc
index	idx
length	len
lexical	lex
maximum	max
minimum	min
number	--	Don't use. Substitute cur or idx for an index, cnt for a count.
pointer	ptr	Don't use in names of actual C pointers, only in the names of array indexes, etc., that act as pointers.
previous	prev
procedure	proc
quantity	qty
record	--	Don't use.
source	src
statement	stmt
structure	--	Don't use.
table	tbl
target	--	Use "destination" (dst) instead.
temporary	tmp
variable	var

Otherwise, try to avoid abbreviations.