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std::basic_string_view<CharT,Traits>::copy

size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;		(since C++17) (until C++20)
constexpr size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;		(since C++20)

Copies the substring [pos, pos + rcount) to the character array pointed to by dest, where rcount is the smaller of count and size() - pos.

Equivalent to Traits::copy(dest, data() + pos, rcount).

Parameters

dest	-	pointer to the destination character string
count	-	requested substring length
pos	-	position of the first character

Return value

Number of characters copied.

Exceptions

std::out_of_range if pos > size().

Complexity

Linear in rcount.

Example

#include <array>
#include <cstddef>
#include <iostream>
#include <stdexcept>
#include <string_view>
 
int main()
{
    constexpr std::basic_string_view<char> source{"ABCDEF"};
    std::array<char, 8> dest;
    std::size_t count{}, pos{};
 
    dest.fill('\0');
    source.copy(dest.data(), count = 4); // pos = 0
    std::cout << dest.data() << '\n'; // ABCD
 
    dest.fill('\0');
    source.copy(dest.data(), count = 4, pos = 1);
    std::cout << dest.data() << '\n'; // BCDE
 
    dest.fill('\0');
    source.copy(dest.data(), count = 42, pos = 2); // ok, count -> 4
    std::cout << dest.data() << '\n'; // CDEF
 
    try
    {
        source.copy(dest.data(), count = 1, pos = 666); // throws: pos > size()
    }
    catch (std::out_of_range const& ex)
    {
        std::cout << ex.what() << '\n';
    }
}

Output:

ABCD
BCDE
CDEF
basic_string_view::copy: __pos (which is 666) > __size (which is 6)