std::nothrow
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nothrow
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Low level memory management
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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 is a constant of it.
[edit] 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
[edit] 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 |