NAME¶

std::basic_string::copy - std::basic_string::copy

Synopsis¶

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

Copies a substring [pos, pos + count) to character string pointed to by dest. If the
requested substring lasts past the end of the string, or if count == npos, the
copied substring is [pos, size()).

The resulting character string is not null-terminated.

Parameters¶

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

Return value¶

Number of characters copied.

Exceptions¶

std::out_of_range if pos > size().

If an exception is thrown for any reason, this function has no effect (strong
exception safety guarantee).

Complexity¶

Linear in count.

Example¶

// Run this code

#include <iostream>
#include <string>

int main()
{
std::string foo("WINE");

// brace-initialization initializes all characters to 0,
// providing a null-terminator
char bar[4]{};

// do not copy the last char, to guarantee null-termination
foo.copy(bar, sizeof bar - 1);

std::cout << bar << '\n'; // requires bar to be null-terminated
}

Output:¶

WIN

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 847 C++98 there was no exception safety added strong exception safety
guarantee guarantee

See also¶

substr returns a substring
(public member function)
copy copies characters
(public member function of std::basic_string_view<CharT,Traits>)
copy copies a range of elements to a new location
copy_if (function template)
(C++11)
memcpy copies one buffer to another
(function)