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std::basic_string<CharT,Traits,Allocator>::max_size

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< cpp‎ | string‎ | basic string
 
 
 
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size_type max_size() const;
(until C++11)
size_type max_size() const noexcept;
(since C++11)
(until C++20)
constexpr size_type max_size() const noexcept;
(since C++20)

Returns the maximum number of elements the string is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the largest string.

Contents

[edit] Parameters

(none)

[edit] Return value

Maximum number of characters.

[edit] Complexity

Constant.

[edit] Example

#include <array>
#include <climits>
#include <iomanip>
#include <iostream>
#include <locale>
#include <string>
#include <typeinfo>
 
#include <boost/core/demangle.hpp>
 
template<typename T>
void print_basic_string_max_size()
{
    std::basic_string<T> s;
    auto max_size = s.max_size();
    std::cout.imbue(std::locale("en_US.UTF-8"));
    std::cout << "basic_string<" << boost::core::demangle(typeid(T).name())
              << ">:\n\t" << max_size << " = ";
    std::cout << std::setprecision(3) << (double) max_size << " = ";
    std::cout.imbue(std::locale("C"));
    std::cout << std::hex << std::setfill('0') << "0x"
              << std::setw(sizeof(typename decltype(s)::size_type) << 1)
              << max_size << '\n' << std::dec;
};
 
int main()
{
    std::cout << "Pointer size: " << CHAR_BIT * sizeof(void*) << " bits\n"
                 "Maximum sizes:\n";
 
    print_basic_string_max_size<char>();
    print_basic_string_max_size<char16_t>();
    print_basic_string_max_size<char32_t>();
    print_basic_string_max_size<wchar_t>();
    print_basic_string_max_size<long>();
 
    using CharT = std::array<char, 01232>;
    print_basic_string_max_size<CharT>();
}

Possible output:

Pointer size: 64 bits
Maximum sizes:
basic_string<char>:
        9,223,372,036,854,775,807 = 9.22e+18 = 0x7fffffffffffffff
basic_string<char16_t>:
        4,611,686,018,427,387,903 = 4.61e+18 = 0x3fffffffffffffff
basic_string<char32_t>:
        2,305,843,009,213,693,951 = 2.31e+18 = 0x1fffffffffffffff
basic_string<wchar_t>:
        2,305,843,009,213,693,951 = 2.31e+18 = 0x1fffffffffffffff
basic_string<long>:
        1,152,921,504,606,846,975 = 1.15e+18 = 0x0fffffffffffffff
basic_string<std::array<char, 666ul>>:
        13,848,906,962,244,407 = 1.38e+16 = 0x00313381ec031337

[edit] See also

returns the number of characters
(public member function) [edit]
returns the maximum number of characters
(public member function of std::basic_string_view<CharT,Traits>) [edit]