std::allocator_traits<Alloc>:: max_size

If possible, obtains the maximum theoretically possible allocation size from the allocator a , by calling a. max_size ( ) .

If the above is not possible (e.g. Alloc does not have the member function max_size() ), then returns std:: numeric_limits < size_type > :: max ( ) / sizeof ( value_type ) .

Parameters

Return value

Theoretical maximum allocation size.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

Example

#include <iostream>
#include <memory>
 
int main()
{
    std::allocator<short> b;
    std::allocator<int> d;
 
    const auto p = std::allocator_traits<decltype(b)>::max_size(b);
    const auto q = std::allocator_traits<decltype(d)>::max_size(d);
 
    std::cout.imbue(std::locale("en_US.UTF-8"));
    std::cout << std::uppercase
              << "p = " << std::dec << p << " = 0x" << std::hex << p << '\n'
              << "q = " << std::dec << q << " = 0x" << std::hex << q << '\n';
}

p = 9,223,372,036,854,775,807 = 0x7,FFF,FFF,FFF,FFF,FFF
q = 4,611,686,018,427,387,903 = 0x3,FFF,FFF,FFF,FFF,FFF

See also