---
title: "noexcept (C++)"
ms.date: "01/12/2018"
f1_keywords: ["noexcept_cpp"]
ms.assetid: df24edb9-c6a6-4e37-9914-fd5c0c3716a8
---
# noexcept (C++)

**C++11:** Specifies whether a function might throw exceptions.

## Syntax

> *noexcept-expression*:
>     **noexcept**
>     **noexcept(** *constant-expression* **)**

### Parameters

*constant-expression*<br/>
A constant expression of type **bool** that represents whether the set of potential exception types is empty. The unconditional version is equivalent to `noexcept(true)`.

## Remarks

A *noexcept expression* is a kind of *exception specification*, a suffix to a function declaration that represents a set of types that might be matched by an exception handler for any exception that exits a function. Unary conditional operator `noexcept(`*constant_expression*`)` where *constant_expression* yeilds **true**, and its unconditional synonym **noexcept**, specify that the set of potential exception types that can exit a function is empty. That is, the function never throws an exception and never allows an exception to be propagated outside its scope. The operator `noexcept(`*constant_expression*`)` where *constant_expression* yeilds **false**, or the absence of an exception specification (other than for a destructor or deallocation function), indicates that the set of potential exceptions that can exit the function is the set of all types.

Mark a function as **noexcept** only if all the functions that it calls, either directly or indirectly, are also **noexcept** or **const**. The compiler does not necessarily check every code path for exceptions that might bubble up to a **noexcept** function. If an exception does exit the outer scope of a function marked `noexcept`, [std::terminate](../standard-library/exception-functions.md#terminate) is invoked immediately, and there is no guarantee that destructors of any in-scope objects will be invoked. Use **noexcept** instead of the dynamic exception specifier `throw()`, which is now deprecated in the standard. We recommended you apply `noexcept` to any function that never allows an exception to propagate up the call stack. When a function is declared **noexcept**, it enables the compiler to generate more efficient code in several different contexts. For more information, see [Exception specifications](exception-specifications-throw-cpp.md).

## Example

A template function that copies its argument might be declared **noexcept** on the condition that the object being copied is a plain old data type (POD). Such a function could be declared like this:

```cpp
#include <type_traits>

template <typename T>
T copy_object(const T& obj) noexcept(std::is_pod<T>)
{
   // ...
}
```

## See also

[C++ Exception Handling](cpp-exception-handling.md)<br/>
[Exception Specifications (throw, noexcept)](exception-specifications-throw-cpp.md)