std::string_view copy() method

od C++20

// Const version only
constexpr size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;

do C++20

// Const version only
size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;

Copies the substring [ pos, pos + rcount ) to the character array pointed to by dest, where rcount is std::min(count, size() - pos).

Equivalent to

Traits::copy(dest, data() + pos, rcount)

The resulting character string_view is not null-terminated.

Parameters

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

Return value

Number of characters copied.

Complexity

Linear in rcount - O(rcount).

Exceptions

Throws std::out_of_range if pos > size().

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';
    }
}

Possible output

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