Question

In an old blog entry titled Cleaner, more elegant, and harder to recognize, the author states:

In C++ it’s not quite so bad because C++ exceptions are raised only at specific points during execution. In C#, exceptions can be raised at any time.

What exactly does he mean by that?

Answer 1

Maybe put it another way:

It is possible in C++ to write functions that offer the nothrow guarantee.

I don’t know C#, and I’m pretty sure Raymond Chen does, so I accept his claim that “In C#, exceptions can be raised at any time”. Therefore, you cannot write functions in C# that offer the nothrow guarantee.

In C++, nothrow functions are quite an important component of functions that offer the other exception guarantees. To make a strong guarantee (that is, to implement transactions), you usually need something like a nothrow swap, that executes more than one statement without interruption by exceptions. To make a basic guarantee, you need nothrow resource cleanup and you may also need short nothrow stretches of code in which your objects’ states violate their class invariants.

Enumerating all the “specific points” in C++ that can throw an exception might be tedious, but in practice it’s not that hard to write a short piece of code that definitely doesn’t. If you can’t do that in C#, that’s an important difference.

If Chen’s claim about C# is wrong, then it probably doesn’t matter what he means. Because he’s wrong.

On a full read of the article, I notice that he’s mostly talking about example code being incorrect (with obvious implications for real code). So if his C# claim is incorrect due to some special cases of C# code that definitely doesn’t throw, but such C# code never appears in tutorial examples, then he would still have an important point about the way the languages are taught — examples that leave out essential stuff that you need to do to make the example code exception safe are probably bad examples, and they risk teaching bad habits. And unlike with error-code examples, the student (says Chen) can’t tell at a glance that the example is bad, and hence might not realise that more work is needed to make them “not-bad”.