C++ Primer, Fifth Edition

18.1.4. The noexcept Exception Specification

It can be helpful both to users and to the compiler to know that a function will not throw any exceptions. Knowing that a function will not throw simplifies the task of writing code that calls that function. Moreover, if the compiler knows that no exceptions will be thrown, it can (sometimes) perform optimizations that must be suppressed if code might throw.

Under the new standard, a function can specify that it does not throw exceptions by providing a noexcept specification. The keyword noexcept following the function parameter list indicates that the function won’t throw:

void recoup(int) noexcept;   // ...