20 Library introduction [library]

20.4 Method of description (Informative) [description]

20.4.2 Other conventions [conventions]

20.4.2.1 Type descriptions [type.descriptions]

20.4.2.1.5 Character sequences [character.seq]

The C standard library makes widespread use of characters and character sequences that follow a few uniform conventions:

(1.1)
A letter is any of the 26 lowercase or 26 uppercase letters in the basic execution character set.
(1.2)
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*),162 or by a change to a locale object, as described in Clauses [locales] and [input.output].
(1.3)
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.

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declared in <clocale> ([c.locales]).

20.4.2.1.5.1 Byte strings [byte.strings]

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.

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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.

A static ntbs is an ntbs with static storage duration.164

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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.

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A string literal, such as "abc", is a static ntbs.

20.4.2.1.5.2 Multibyte strings [multibyte.strings]

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.165

A static ntmbs is an ntmbs with static storage duration.

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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.