std::copy使用方法

推荐2个c++函数库，类定义的资料库：

http://en.cppreference.com/w/cpp/algorithm/copy

http://www.cplusplus.com/reference/algorithm/copy/?kw=copy

---------------------------------------------------------------------------------------------------------------

Defined in header <algorithm>
template< class InputIt, class OutputIt >
     OutputIt copy( InputIt first, InputIt last, OutputIt d_first );

Copies the elements in the range, defined by [first, last), to another range beginning at d_first. 

Parameters

first, last

            Input iterators to the initial and final positions in a sequence to be copied. The range used is [first,last), which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.

            c++中的区间几乎都是左开右闭的，包括一些类的构造函数，比如 int a[5] = { 1, 2, 3, 4, 5};  set<int> s(&a[0], &a[4]); s里只会插入{ 1，2，3，4 }这4个元素。

d_first

            Output iterator to the initial position in the destination sequence.
            This shall not point to any element in the range [first,last).

Return value

An iterator to the end of the destination range where elements have been copied.

Complexity

Linear in the distance between first and last: Performs an assignment operation for each element in the range.

Example

The following code uses copy to both copy the contents of one vector to another and to display the resulting vector:

#include <algorithm>
#include <iostream>
#include <vector>
#include <iterator>
#include <numeric>
 
int main()
{
    std::vector<int> from_vector(10);
    std::iota(from_vector.begin(), from_vector.end(), 0);
 
    std::vector<int> to_vector;
    std::copy(from_vector.begin(), from_vector.end(),
              std::back_inserter(to_vector));
// or, alternatively,
//  std::vector<int> to_vector(from_vector.size());
//  std::copy(from_vector.begin(), from_vector.end(), to_vector.begin());
// either way is equivalent to
//  std::vector<int> to_vector = from_vector;
 
    std::cout << "to_vector contains: ";
 
    std::copy(to_vector.begin(), to_vector.end(),
              std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

Output:

to_vector contains: 0 1 2 3 4 5 6 7 8 9