[character.seq] # 16 Library introduction [[library]](./#library) ## 16.3 Method of description [[description]](description#character.seq) ### 16.3.3 Other conventions [[conventions]](conventions#character.seq) #### 16.3.3.3 Type descriptions [[type.descriptions]](type.descriptions#character.seq) #### 16.3.3.3.4 Character sequences [character.seq] #### [16.3.3.3.4.1](#general) General [[character.seq.general]](character.seq.general) [1](#general-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L720) The C standard library makes widespread useof characters and character sequences that follow a few uniform conventions: - [(1.1)](#general-1.1) Properties specified as [*locale-specific*](#def:locale-specific "16.3.3.3.4.1 General [character.seq.general]") may change during program execution by a call to setlocale(int, const char*) ([[clocale.syn]](clocale.syn "28.3.5.1 Header synopsis")), or by a change to a locale object, as described in [[locales]](locales "28.3.3 Locales") and [[input.output]](input.output "31 Input/output library")[.](#general-1.1.sentence-1) - [(1.2)](#general-1.2) The [*execution character set*](#def:character_set,execution "16.3.3.3.4.1 General [character.seq.general]") and the [*execution wide-character set*](#def:wide-character_set,execution "16.3.3.3.4.1 General [character.seq.general]") are supersets of the basic literal character set ([[lex.charset]](lex.charset "5.3.1 Character sets"))[.](#general-1.2.sentence-1) The encodings of the execution character sets and the sets of additional elements (if any) are locale-specific[.](#general-1.2.sentence-2) Each element of the execution wide-character set is encoded as a single code unit representable by a value of type wchar_t[.](#general-1.2.sentence-3) [*Note [1](#general-note-1)*: The encodings of the execution character sets can be unrelated to any literal encoding[.](#general-1.2.sentence-4) — *end note*] - [(1.3)](#general-1.3) A [*letter*](#def:letter "16.3.3.3.4.1 General [character.seq.general]") is any of the 26 lowercase or 26uppercase letters in the basic character set[.](#general-1.3.sentence-1) - [(1.4)](#general-1.4) The[*decimal-point character*](#def:character,decimal-point "16.3.3.3.4.1 General [character.seq.general]") is the locale-specific (single-byte) character used by functions that convert between a (single-byte) character sequence and a value of one of the floating-point types[.](#general-1.4.sentence-1) It is used in the character sequence to denote the beginning of a fractional part[.](#general-1.4.sentence-2) It is represented in [[support]](support "17 Language support library") through [[exec]](exec "33 Execution control library") and [[depr]](depr "Annex D (normative) Compatibility features") by a period,'.', which is also its value in the "C" locale[.](#general-1.4.sentence-3) - [(1.5)](#general-1.5) A[*character sequence*](#def:character_sequence "16.3.3.3.4.1 General [character.seq.general]") is an [array object](dcl.array "9.3.4.5 Arrays [dcl.array]") *A* that can be declared as*T A*[*N*], where *T* is any of the typeschar,unsigned char, orsigned char ([[basic.fundamental]](basic.fundamental "6.9.2 Fundamental types")), optionally qualified by any combination ofconst orvolatile[.](#general-1.5.sentence-1) The initial elements of the array have defined contents up to and including an element determined by some predicate[.](#general-1.5.sentence-2) A character sequence can be designated by a pointer value*S* that points to its first element[.](#general-1.5.sentence-3) #### [16.3.3.3.4.2](#byte.strings) Byte strings [[byte.strings]](byte.strings) [1](#byte.strings-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L788) A [*null-terminated byte string*](#def:ntbs "16.3.3.3.4.2 Byte strings [byte.strings]"), or ntbs, is a character sequence whose highest-addressed element with defined content has the value zero (the [*terminating null character*](#def:character,terminating_null "16.3.3.3.4.2 Byte strings [byte.strings]")); no other element in the sequence has the value zero[.](#byte.strings-1.sentence-1)[139](#footnote-139 "Many of the objects manipulated by function signatures declared in 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.") [2](#byte.strings-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L803) The [*length of an ntbs*](#def:ntbs,length "16.3.3.3.4.2 Byte strings [byte.strings]") is the number of elements that precede the terminating null character[.](#byte.strings-2.sentence-1) An [*empty ntbs*](#def:ntbs,empty "16.3.3.3.4.2 Byte strings [byte.strings]") has a length of zero[.](#byte.strings-2.sentence-2) [3](#byte.strings-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L810) The [*value of an ntbs*](#def:ntbs,value "16.3.3.3.4.2 Byte strings [byte.strings]") is the sequence of values of the elements up to and including the terminating null character[.](#byte.strings-3.sentence-1) [4](#byte.strings-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L815) A [*static ntbs*](#def:ntbs,static "16.3.3.3.4.2 Byte strings [byte.strings]") is an ntbs with static storage duration[.](#byte.strings-4.sentence-1)[140](#footnote-140 "A string-literal, such as "abc", is a static ntbs.") [139)](#footnote-139)[139)](#footnoteref-139) Many of the objects manipulated by function signatures declared in[](cstring.syn#header:%3ccstring%3e "27.5.1 Header synopsis [cstring.syn]") are character sequences or ntbss[.](#footnote-139.sentence-1) The size of some of these character sequences is limited by a length value, maintained separately from the character sequence[.](#footnote-139.sentence-2) [140)](#footnote-140)[140)](#footnoteref-140) A [*string-literal*](lex.string#nt:string-literal "5.13.5 String literals [lex.string]"), such as"abc", is a static ntbs[.](#footnote-140.sentence-1) #### [16.3.3.3.4.3](#multibyte.strings) Multibyte strings [[multibyte.strings]](multibyte.strings) [1](#multibyte.strings-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L827) A [*multibyte character*](#def:character,multibyte "16.3.3.3.4.3 Multibyte strings [multibyte.strings]") is a sequence of one or more bytes representing the code unit sequence for an encoded character of the execution character set[.](#multibyte.strings-1.sentence-1) [2](#multibyte.strings-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L834) A [*null-terminated multibyte string*](#def:ntmbs "16.3.3.3.4.3 Multibyte strings [multibyte.strings]"), or ntmbs, is an ntbs that constitutes a sequence of valid multibyte characters, beginning and ending in the initial shift state[.](#multibyte.strings-2.sentence-1)[141](#footnote-141 "An ntbs that contains characters only from the basic literal character set is also an ntmbs. Each multibyte character then consists of a single byte.") [3](#multibyte.strings-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L847) A [*static ntmbs*](#def:ntmbs,static "16.3.3.3.4.3 Multibyte strings [multibyte.strings]") is an ntmbs with static storage duration[.](#multibyte.strings-3.sentence-1) [141)](#footnote-141)[141)](#footnoteref-141) An ntbs that contains characters only from the basic literal character set is also an ntmbs[.](#footnote-141.sentence-1) Each multibyte character then consists of a single byte[.](#footnote-141.sentence-2)