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Difference between revisions of "cpp/string/basic string/at"

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< cpp‎ | string‎ | basic string
(Added LWG issue #847 DR (part 4).)
m (→‎Exceptions: pl.)
Line 29: Line 29:
 
Throws {{lc|std::out_of_range}} if {{c|1=pos >= size()}}.
 
Throws {{lc|std::out_of_range}} if {{c|1=pos >= size()}}.
  
−
{{cpp/strong exception safety guarantee}}
+
{{cpp/strong exception safety guarantee|plural=yes}}
  
 
===Complexity===
 
===Complexity===

Revision as of 08:14, 1 August 2023

 
C++
 
Strings library
 
std::basic_string
Member functions
(C++23)
Element access
basic_string::at
(DR*)
(DR*)
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
(DR*)
Modifiers
(C++23)
(DR*)
(C++23)
(C++23)
(C++23)  
Search
Operations
(C++20)
(C++20)
(C++23)
Constants
Non-member functions
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversions
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

 
(1)
reference at( size_type pos );
 (until C++20)
constexpr reference at( size_type pos );
 (since C++20)
(2)
const_reference at( size_type pos ) const;
 (until C++20)
constexpr const_reference at( size_type pos ) const;
 (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

Parameters

pos - position of the character to return

Return value

Reference to the requested character.

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).

Complexity

Constant.

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

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

See also

 accesses the specified character
(public member function) [edit]
accesses the specified character with bounds checking
(public member function of std::basic_string_view<CharT,Traits>) [edit]
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