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noreturn

Visual Studio 2010

This __declspec attribute tells the compiler that a function does not return. As a consequence, the compiler knows that the code following a call to a __declspec(noreturn) function is unreachable.

If the compiler finds a function with a control path that does not return a value, it generates a warning (C4715) or error message (C2202). If the control path cannot be reached due to a function that never returns, you can use __declspec(noreturn) to prevent this warning or error.

Note
Adding __declspec(noreturn) to a function that is expected to return can result in undefined behavior.

Example

In the following sample,the else clause does not contain a return statement. Declaring fatal as __declspec(noreturn) avoids an error or warning message.

Copy

// noreturn2.cpp
__declspec(noreturn) extern void fatal () {}

int main() {
   if(1)
     return 1;
   else if(0)
     return 0;
   else
     fatal();
}

Reference

__declspec

C++ Keywords

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FAQ

Poor choice of function in the example

As the standard defined behavior for the main function is to add "return 0" implicitly when reaching an end of it, removing the modifier will have no effect here. However for any other function it will be certainly recommended.

History

12/1/2011
Łukasz Mendakiewicz