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An identifier (name) in C is a sequence of letters and digits, as well as ‘_’, that does not start with a digit. Most compilers also allow ‘$’. An identifier can be as long as you like; for example,
int anti_dis_establishment_arian_ism;
Letters in identifiers are case-sensitive in C; thus, a
and A
are two different identifiers.
Identifiers in C are used as variable names, function names, typedef
names, enumeration constants, type tags, field names, and labels.
Certain identifiers in C are keywords, which means they have
specific syntactic meanings. Keywords in C are reserved words,
meaning you cannot use them in any other way. For instance, you can’t
define a variable or function named return
or if
.
You can also include other characters, even non-ASCII characters, in identifiers by writing their Unicode character names, which start with ‘\u’ or ‘\U’, in the identifier name. See Unicode Character Codes. However, it is usually a bad idea to use non-ASCII characters in identifiers, and when the names are written in English, they never need non-ASCII characters. See English.
As stated above, whitespace is required to separate two consecutive identifiers, or to separate an identifier from a preceding or following numeric constant.