21 Strings library [strings]

21.2 Character traits [char.traits]

21.2.1 Character traits requirements [char.traits.require]

In Table [tab:char.traits.require], X denotes a Traits class defining types and functions for the character container type CharT; c and d denote values of type CharT; p and q denote values of type const CharT*; s denotes a value of type CharT*; n, i and j denote values of type std::size_t; e and f denote values of type X::int_type; pos denotes a value of type X::pos_type; state denotes a value of type X::state_type; and r denotes an lvalue of type CharT. Operations on Traits shall not throw exceptions.

Table 62 — Character traits requirements
ExpressionReturn typeAssertion/noteComplexity
X::char_type charT (described in [char.traits.typedefs]) compile-time
X::int_type (described in [char.traits.typedefs]) compile-time
X::off_type (described in [char.traits.typedefs]) compile-time
X::pos_type (described in [char.traits.typedefs]) compile-time
X::state_type (described in [char.traits.typedefs]) compile-time
X::eq(c,d) bool yields: whether c is to be treated as equal to d. constant
X::lt(c,d) bool yields: whether c is to be treated as less than d. constant
X::compare(p,q,n) int yields: 0 if for each i in [0,n), X::eq(p[i],q[i]) is true; else, a negative value if, for some j in [0,n), X::lt(p[j],q[j]) is true and for each i in [0,j) X::eq(p[i],q[i]) is true; else a positive value. linear
X::length(p) std::size_t yields: the smallest i such that X::eq(p[i],charT()) is true. linear
X::find(p,n,c) const X::char_type* yields: the smallest q in [p,p+n) such that X::eq(*q,c) is true, zero otherwise. linear
X::move(s,p,n) X::char_type* for each i in [0,n), performs X::assign(s[i],p[i]). Copies correctly even where the ranges [p,p+n) and [s,s+n) overlap. yields: s. linear
X::copy(s,p,n) X::char_type* pre: p not in [s,s+n). yields: s. for each i in [0,n), performs X::assign(s[i],p[i]). linear
X::assign(r,d) (not used) assigns r=d. constant
X::assign(s,n,c) X::char_type* for each i in [0,n), performs X::assign(s[i],c). yields: s. linear
X::not_eof(e) int_type yields: e if X::eq_int_type(e,X::eof()) is false, otherwise a value f such that X::eq_int_type(f,X::eof()) is false. constant
X::to_char_type(e) X::char_type yields: if for some c, X::eq_int_type(e,X::to_int_type(c)) is true, c; else some unspecified value. constant
X::to_int_type(c) X::int_type yields: some value e, constrained by the definitions of to_char_type and eq_int_type. constant
X::eq_int_type(e,f) bool yields: for all c and d, X::eq(c,d) is equal to X::eq_int_type(X::to_int_type(c), X::to_int_type(d)); otherwise, yields true if e and f are both copies of X::eof(); otherwise, yields false if one of e and f is a copy of X::eof() and the other is not; otherwise the value is unspecified. constant
X::eof() X::int_type yields: a value e such that X::eq_int_type(e,X::to_int_type(c)) is false for all values c. constant

The struct template

template<class charT> struct char_traits;

shall be provided in the header <string> as a basis for explicit specializations.