std::nothrow

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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

Example

Run this code
#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

 allocation functions
(function)
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