20 Strings library [strings]

20.2 Character traits [char.traits]

20.2.1 Character traits requirements [char.traits.require]

In Table 58, X denotes a traits class defining types and functions for the character container type C; c and d denote values of type C; p and q denote values of type const C*; s denotes a value of type C*; n, i and j denote values of type size_­t; e and f denote values of type X::int_­type; pos denotes a value of type X::pos_­type; and r denotes an lvalue of type C.
Operations on X shall not throw exceptions.
Table 58 — Character traits requirements
Expression
Return type
Assertion/note
Complexity
pre-/post-condition
X::char_­type
C
compile-time
X::int_­type
(described in [char.traits.typedefs])
compile-time
X::off_­type
compile-time
X::pos_­type
compile-time
X::state_­type
(described in [char.traits.typedefs])
compile-time
X::eq(c,d)
bool
Returns: whether c is to be treated as equal to d.
constant
X::lt(c,d)
bool
Returns: whether c is to be treated as less than d.
constant
X::compare(p,q,n)
int
Returns: 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)
size_­t
Returns: the smallest i such that X::eq(p[i],charT()) is true.
linear
X::find(p,n,c)
const X::char_­type*
Returns: 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.

Returns: s.
linear
X::copy(s,p,n)
X::char_­type*
Expects: p not in [s, s+n).

Returns: 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).

Returns: s.
linear
X::not_­eof(e)
int_­type
Returns: 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
Returns: 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
Returns: some value e, constrained by the definitions of to_­char_­type and eq_­int_­type.
constant
X::eq_­int_­type(e,f)
bool
Returns: 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
Returns: a value e such that X::eq_­int_­type(e,X::to_­int_­type(c)) is false for all values c.
constant
The class template
template<class charT> struct char_traits;
is provided in the header <string> as a basis for explicit specializations.