The pair<T1,T2> is a simple and handy way to
carry around a pair of objects. One is of type T1, and another of
type T2; they may be the same type, but you don't get anything
extra if they are. The two members can be accessed directly, as
.first and .second.
Construction is simple. The default ctor initializes each member with its respective default ctor. The other simple ctor,
pair (const T1& x, const T2& y);
does what you think it does, first getting x
and second getting y.
There is a copy constructor, but it requires that your compiler handle member function templates:
template <class U, class V> pair (const pair<U,V>& p);
The compiler will convert as necessary from U to T1 and from V to T2 in order to perform the respective initializations.
The comparison operators are done for you. Equality
of two pair<T1,T2>s is defined as both first
members comparing equal and both second members comparing
equal; this simply delegates responsibility to the respective
operator== functions (for types like MyClass) or builtin
comparisons (for types like int, char, etc).
The less-than operator is a bit odd the first time you see it. It is defined as evaluating to:
x.first < y.first ||
( !(y.first < x.first) && x.second < y.second )
The other operators are not defined using the rel_ops
functions above, but their semantics are the same.
Finally, there is a template function called make_pair
that takes two references-to-const objects and returns an
instance of a pair instantiated on their respective types:
pair<int,MyClass> p = make_pair(4,myobject);
The pair<T1,T2> is a simple and handy way to
d17 2
a18 1
There is a constructor template for copying pairs of other types: d34 1 a34 1 ( !(y.first < x.first) && x.second < y.second ) d42 1 a42 4
The pair<T1,T2> is a simple and handy way to
d17 2
a18 1
There is a constructor template for copying pairs of other types: d34 1 a34 1 ( !(y.first < x.first) && x.second < y.second ) d42 1 a42 4
The pair<T1,T2> is a simple and handy way to
d17 2
a18 1
There is a constructor template for copying pairs of other types: d34 1 a34 1 ( !(y.first < x.first) && x.second < y.second ) d42 1 a42 4