std::allocator_traits<Alloc>::max_size
From cppreference.com
< cpp | memory | allocator traits
| Defined in header <memory>
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static size_type max_size( const Alloc& a ) noexcept; |
(since C++11) (constexpr since C++20) |
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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
| a | - | allocator to detect |
Return value
Theoretical maximum allocation size.
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 2162 | C++11 | max_size was not requied to be noexcept
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required |
| LWG 2466 | C++11 | theoretical maximum allocation size in bytes was returned as fallback | size in elements is returned |
Example
Run this code
#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'; }
Possible output:
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
| (until C++20) |
returns the largest supported allocation size (public member function of std::allocator<T>) |