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std::basic_string<CharT,Traits,Allocator>::copy

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< cpp‎ | string‎ | basic string
 
 
 
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size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;
(until C++20)
constexpr size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;
(since C++20)

Copies a substring [pospos + 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 [possize()).

The resulting character string is not null-terminated.

Contents

[edit] Parameters

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

[edit] Return value

Number of characters copied.

[edit] 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).

[edit] Complexity

Linear in count.

[edit] Example

#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

[edit] 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 guarantee added strong exception safety guarantee

[edit] See also

returns a substring
(public member function) [edit]
copies characters
(public member function of std::basic_string_view<CharT,Traits>) [edit]
copies a range of elements to a new location
(function template) [edit]
copies one buffer to another
(function) [edit]