The C standard library makes widespread use of characters and character sequences that follow a few uniform conventions:
A letter is any of the 26 lowercase or 26 uppercase letters in the basic execution character set.168
The decimal-point character is the (single-byte) character used by functions that convert between a (single-byte) character sequence and a value of one of the floating-point types. It is used in the character sequence to denote the beginning of a fractional part. It is represented in Clauses [language.support] through [thread] and Annex [depr] by a period, '.', which is also its value in the "C" locale, but may change during program execution by a call to setlocale(int, const char*),169 or by a change to a locale object, as described in Clauses [locales] and [input.output].
A character sequence is an array object ([dcl.array]) A that can be declared as T A[N], where T is any of the types char, unsigned char, or signed char ([basic.fundamental]), optionally qualified by any combination of const or volatile. The initial elements of the array have defined contents up to and including an element determined by some predicate. A character sequence can be designated by a pointer value S that points to its first element.
Note that this definition differs from the definition in ISO C 7.1.1.
declared in <clocale> ([c.locales]).
A null-terminated byte string, or ntbs, is a character sequence whose highest-addressed element with defined content has the value zero (the terminating null character); no other element in the sequence has the value zero.170
The length of an ntbs is the number of elements that precede the terminating null character. An empty ntbs has a length of zero.
The value of an ntbs is the sequence of values of the elements up to and including the terminating null character.
Many of the objects manipulated by function signatures declared in <cstring> ([c.strings]) are character sequences or ntbss. The size of some of these character sequences is limited by a length value, maintained separately from the character sequence.
A string literal, such as "abc", is a static ntbs.
A null-terminated multibyte string, or ntmbs, is an ntbs that constitutes a sequence of valid multibyte characters, beginning and ending in the initial shift state.172
An ntbs that contains characters only from the basic execution character set is also an ntmbs. Each multibyte character then consists of a single byte.