std::basic_string<CharT,Traits,Allocator>::copy
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basic_string::copy
(C++20)
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(C++20)(C++20)
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(C++11)
size_type copy( CharT* dest, size_type count, size_type pos = 0 ) const;
(constexpr since C++20)
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.
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
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
[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 |