std::basic_string<CharT,Traits,Allocator>::operator[]

 

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basic_string

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std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

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CharT& operator[]( size_type pos );	(1)	(constexpr since C++20)
const CharT& operator[]( size_type pos ) const;	(2)	(constexpr since C++20)

Returns a reference to the character at specified location pos if pos < size(), or a reference to CharT() if pos == size(). No bounds checking is performed.

If pos > size(), the behavior is undefined.

For overload (1), if pos == size(), the behavior is undefined if the object referred by the returned reference is modified to any value other than CharT()(since C++11).

Parameters

pos

-

position of the character to return

Return value

*(begin() + pos) if pos < size(), or a reference to CharT() if pos == size().

Complexity

Constant.

Example

Run this code

#include <iostream>
#include <string>
 
int main()
{
    const std::string e("Exemplar");
    for (unsigned i = e.length() - 1; i != 0; i /= 2)
        std::cout << e[i];
    std::cout << '\n';
 
    const char* c = &e[0];
    std::cout << c << '\n'; // print as a C string
 
    // Change the last character of s into a 'y'
    std::string s("Exemplar ");
    s[s.size() - 1] = 'y'; // equivalent to s.back() = 'y';
    std::cout << s << '\n';
}

Output:

rmx
Exemplar
Exemplary

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 259	C++98	non-const overload could return const lvalue data()[pos], which was ill-formed	changed to return *(begin() + pos)
LWG 2475	C++11	if pos == size(), the behavior of modifying the object referred by the returned reference was undefined	well-defined if modified to CharT()

See also

at	accesses the specified character with bounds checking (public member function)
front (DR*)	accesses the first character (public member function)
back (DR*)	accesses the last character (public member function)
operator[]	accesses the specified character (public member function of std::basic_string_view<CharT,Traits>)