Книга: Standard Template Library Programmer

copy_n

copy_n

Category: algorithms

Component type: function

template <class InputIterator, class Size, class OutputIterator>
OutputIterator copy_n(InputIterator first, Size count, OutputIterator result);

Copy_n copies elements from the range [first, first + n) to the range [result, result + n). That is, it performs the assignments *result = *first, *(result + 1) = *(first + 1), and so on. Generally, for every integer i from 0 up to (but not including) n, copy_n performs the assignment *(result + i) = *(first + i). Assignments are performed in forward order, i.e. in order of increasing n. [1]

The return value is result + n.

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h. This function is an SGI extension; it is not part of the C++ standard.

• InputIterator is a model of Input Iterator.

• OutputIterator is a model of Output Iterator.

• Size is an integral type.

• InputIterator's value type is convertible to a type in OutputIterator's set of value types.

• n >= 0.

• [first, first + n) is a valid range.

• result is not an iterator within the range [first, first + n).

• [result, result + n) is a valid range.

Linear. Exactly n assignments are performed.

vector<int> V(5);
iota(V.begin(), V.end(), 1);
list<int> L(V.size());
copy_n(V.begin(), V.size(), L.begin());
assert(equal(V.begin(), V.end(), L.begin()));

[1] Copy_n is almost, but not quite, redundant. If first is an input iterator, as opposed to a forward iterator, then the copy_n operation can't be expressed in terms of copy.

copy, copy_backward

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