Note that every member of a Character Traits class is static.
There is never any need to create a Character Traits object, and, in
fact, there is no guarantee that creating such objects is possible.
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Value type
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X::char_type
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The character type described by this Character Traits type.
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Int type
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X::int_type
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A type that is capable of representing every valid value of type
char_type, and, additionally an end-of-file value. For char,
for example, the int type may be int, and for wchar_t it may
be wint_t.
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Position type
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X::pos_type
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A type that can represent the position of a character of type
char_type within a file. This type is usually streampos.
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Offset type
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X::off_type
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An integer type that can represent the difference between two
pos_type values. This type is usually streamoff.
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State type
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X::state_type
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A type that can represent a state in a multibyte encoding
scheme. This type, if used at all, is usually mbstate_t.
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Name
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Expression
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Precondition
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Semantics
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Postcondition
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Character assignment
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X::assign(c1, c2)
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Performs the assignment c1 = c2
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X::eq(c1, c2) is true.
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Character equality
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X::eq(c1, c2)
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Returns true if and only if c1 and c2 are equal.
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Character comparison
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X::lt(c1, c2)
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Returns true if and only if c1 is less than c2. Note that
for any two value values c1 and c2, exactly one of
X::lt(c1, c2), X::lt(c2, c1), and X::eq(c1, c2) should be
true.
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Range comparison
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X::compare(p1, p2, n)
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[p1, p1+n) and [p2, p2+n) are valid ranges.
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Generalization of strncmp. Returns 0 if every element
in [p1, p1+n) is equal to the corresponding element
in [p2, p2+n), a negative value if there exists an element
in [p1, p1+n) less than the corresponding element in [p2, p2+n)
and all previous elements are equal, and a positive value
if there exists an element in [p1, p1+n) greater than the
corresponding element in [p2, p2+n) and all previous elements
are equal.
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Length
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X::length(p)
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Generalization of strlen.
Returns the smallest non-negative number n such that
X::eq(p+n, X::char_type()) is true. Behavior is undefined
if no such n exists.
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Find
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X::find(p, n, c)
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[p, p+n) is a valid range.
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Generalization of strchr. Returns the first pointer q
in [p, p+n) such that X::eq(*q, c) is true. Returns a
null pointer if no such pointer exists. (Note that this method
for indicating a failed search differs from that is
find.)
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Move
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X::move(s, p, n)
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[p, p+n) and [s, s+n) are valid ranges (possibly overlapping).
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Generalization of memmove. Copies values from the range
[p, p+n) to the range [s, s+n), and returns s.
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Copy
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X::copy(s, p, n)
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[p, p+n) and [s, s+n) are valid ranges which do not overlap.
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Generalization of memcpy. Copies values from the range
[p, p+n) to the range [s, s+n), and returns s.
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Range assignment
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X::assign(s, n, c)
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[s, s+n) is a valid range.
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Generalization of memset. Assigns the value c to each pointer
in the range [s, s+n), and returns s.
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EOF value
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X::eof()
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Returns a value that can represent EOF.
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X::eof() is distinct from every valid value of type
X::char_type. That is, there exists no value c
such that X::eq_int_type(X::to_int_type(c), X::eof()) is true.
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Not EOF
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X::not_eof(e)
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Returns e if e represents a valid char_type value, and some
non-EOF value if e is X::eof().
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Convert to value type
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X::to_char_type(e)
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Converts e to X's char type. If e is a representation of some
char_type value then it returns that value; if e is X::eof()
then the return value is unspecified.
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Convert to int type
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X::to_int_type(c)
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Converts c to X's int type.
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X::to_char_type(X::to_int_type(c)) is a null operation.
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Equal int type values
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X::eq_int_type(e1, e2)
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Compares two int type values. If there exist values of type
X::char_type such that e1 is X::to_int_type(c1)) and
e2 is X::to_int_type(c2)), then X::eq_int_type(e1, e2) is
the same as X::eq(c1, c2). Otherwise, eq_int_type returns
true if e1 and e2 are both EOF and false if one of
e1 and e2 is EOF and the other is not.
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