std::basic_string<CharT,Traits,Allocator>::at
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(C++23)
basic_string::at
(DR*)
(DR*)
(C++23)
(DR*)
(C++23)
(C++23)
(C++20)
(C++20)
(C++23)
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++14)
(C++11)
CharT& at( size_type pos );
(1)
(constexpr since C++20)
const CharT& at( size_type pos ) const;
(2)
(constexpr since C++20)
Returns a reference to the character at specified location pos. Bounds checking is performed, exception of type std::out_of_range will be thrown on invalid access.
Contents
[edit] Parameters
pos
-
position of the character to return
[edit] Return value
Reference to the requested character.
[edit] Exceptions
Throws std::out_of_range if pos >= size().
If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee).
[edit] Complexity
Constant.
[edit] Example
Run this code
#include <iostream> #include <stdexcept> #include <string> int main() { std::string s("message"); // for capacity s = "abc"; s.at(2) = 'x'; // OK std::cout << s << '\n'; std::cout << "string size = " << s.size() << '\n'; std::cout << "string capacity = " << s.capacity() << '\n'; try { // This will throw since the requested offset is greater than the current size. s.at(3) = 'x'; } catch (std::out_of_range const& exc) { std::cout << exc.what() << '\n'; } }
Possible output:
abx string size = 3 string capacity = 7 basic_string::at
[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 |
| LWG 2207 | C++98 | the behavior was undefined if pos >= size() is true | always throws an exception in this case |