From: "Dill, John" <john-dill@uiowa.edu>

"Rob Stewart" <stewart@sig.com> wrote in message news:<200404201905.i3KJ55e08992@lawrencewelk.systems.susq.com>...

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From: "Dill, John" <john-dill@uiowa.edu>

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I am wondering about the use-case of numeric_cast in this sample.

unsigned char uchar_max = std::numeric_limits<unsigned char>::max(); char schar_value = 0;

try { schar_value = boost::numeric_cast<char>( uchar_max ); } catch ( boost::bad_numeric_cast ) { std::cout << "Overflow occurred..." << std::endl; }

When I execute this sample, I don't get the exception. What's the background on this behavior? I'm using gcc 3.3.1.

Your char is unsigned.

I'd like to know why conceptually the exception isn't thrown.

As I said, in too few words, is that your "char" is unsigned, so "char" and "unsigned char" are essentially the same type. Technically, they are distinct types (for overloading purposes, for example), but they are both unsigned and the same size, so: assert(std::numeric_limits<char>::max() == std::numeric_limits<unsigned char>::max()); on your system.

Why is it beneficial to have unsigned T to signed T overflows not be detected? It is not just char, but short, int, and long as well.

Now that's another story. Changing "unsigned char" to "unsigned" and "char" to "int" should cause an exception. If that's not happening, I don't understand since std::numeric_limits<unsigned>::max() is greater than std::numeric_limits<int>::max().

If this was the intended behavior, then what is the reasoning behind it?

What you describe isn't the intended behavior other than the char problem. -- Rob Stewart stewart@sig.com Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;