Why add a throw() to your methods?

Towards the end of the comments in my last "What's wrong with this code" , hippietim asked why I added a throw()attribute to the destructor of the CCoInitializer.  The answer's pretty simple.  If you add a throw() attribute around routines that never throw, the compiler can be clever about code motion and optimization.  Consider the following totally trivial:

class

MyClass
{
size_t CalculateFoo()
{
:
:
};
size_t MethodThatCannotThrow() throw()
{
        return 100;
};
    void ExampleMethod()
{
size_t foo, bar;
try
{
foo = CalculateFoo();
bar = foo * 100;
MethodThatCannotThrow();
printf("bar is %d", bar);
}
catch (...)
{
}
}
};

When the compiler sees this, with the "throw()" attribute, the compiler can completely optimize the "bar" variable away, because it knows that there is no way for an exception to be thrown from MethodThatCannotThrow().  Without the throw() attribute, the compiler has to create the "bar" variable, because if MethodThatCannotThrow throws an exception, the exception handler may/will depend on the value of the bar variable.

In addition, source code analysis tools like prefast can (and will) use the throw() annotation to improve their error detection capabilities - for example, if you have a try/catch and all the functions you call are marked as throw(), you don't need the try/catch (yes, this has a problem if you later call a function that could throw).