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Showing content from https://en.cppreference.com/w/cpp/language/../memory/weak_ptr/../../string/basic_string/back.html below:

std::basic_string<CharT,Traits,Allocator>::back - cppreference.com

CharT& back();

(1) (constexpr since C++20)

const CharT& back() const;

(2) (constexpr since C++20)

Returns reference to the last character in the string.

If empty() is true, the behavior is undefined.

(until C++26)

If empty() is true:

If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under âobserveâ evaluation semantic, the behavior is undefined.
If the implementation is not hardened, the behavior is undefined.

(since C++26) [edit] Return value

operator[](size() - 1)

[edit] Complexity

Constant.

[edit] Notes

In libstdc++, back() is not available in C++98 mode.

[edit] Example

#include <iostream>
#include <string>
 
int main()
{
    std::string s("Exemplary");
    char& back1 = s.back();
    back1 = 's';
    std::cout << s << '\n'; // "Exemplars"
 
    std::string const c("Exemplary");
    char const& back2 = c.back();
    std::cout << back2 << '\n'; // 'y'
}

Output:

[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 534 C++98 std::basic_string did not have the member function back() added [edit] See also accesses the first character
(public member function) [edit] accesses the last character
(public member function of std::basic_string_view<CharT,Traits>) [edit]

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