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| Category: algorithms | | Component type: function |
template <class Assignable>
void swap(Assignable& a, Assignable& b);
Assigns the contents of
a to
b and the contents of
b to
a. This is used as a primitive operation by many other algorithms.
Defined in the standard header
algorithm, and in the nonstandard backward-compatibility header
algo.h.
None.
Amortized constant time.
[1] [2]
int x = 1;
int y = 2;
assert(x == 1 && y == 2);
swap(x, y);
assert(x == 2 && y == 1);
[1] The time required to
swap two objects of type
T will obviously depend on the type; "constant time" does not mean that performance will be the same for an 8-bit
char as for a 128-bit
complex<double>.
[2] This implementation of swap makes one call to a copy constructor and two calls to an assignment operator; roughly, then, it should be expected to take about the same amount of time as three assignments. In many cases, however, it is possible to write a specialized version of swap that is far more efficient. Consider, for example, swapping two Vector<double>s each of which has N elements. The unspecialized version requires 3*N assignments of double, but a specialized version requires only nine pointer assignments. This is important because swap is used as a primitive operation in many other STL algorithms, and because containers of containers (List<Vector<char> >, for example) are very common. The STL includes specialized versions of swap for all container classes. User-defined types should also provide specialized versions of swap whenever it is possible to write one that is more efficient than the general version.
iter_swap,
swap_ranges
