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.
| Expression | Return type | Assertion/note | Complexity |
| pre-/post-condition | |||
| 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.