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std::nothrow - cppreference.com

From cppreference.com

Defined in header <new>

(1)

struct nothrow_t {};

 (until C++11)

struct nothrow_t { explicit nothrow_t() = default; };

 (since C++11)

extern const std::nothrow_t nothrow;

 (2)

std::nothrow_t is an empty class type used to disambiguate the overloads of throwing and non-throwing allocation functions. std::nothrow is a constant of it.

Example

#include <iostream>
#include <new>

int main()
{
    try
    {
        while (true)
        {
            new int[100000000ul];   // throwing overload
        }
    }
    catch (const std::bad_alloc& e)
    {
        std::cout << e.what() << '\n';
    }

    while (true)
    {
        int* p = new(std::nothrow) int[100000000ul]; // non-throwing overload
        if (p == nullptr)
        {
            std::cout << "Allocation returned nullptr\n";
            break;
        }
    }
}

Output: 

std::bad_alloc
Allocation returned nullptr

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 2510 C++11 the default constructor was non-explicit, which could lead to ambiguity made explicit

See also