or is not valid C++ : why does this code compile?

c++ or-operator
Jérôme picture Jérôme · Sep 16, 2009 · Viewed 9.3k times · Source

Here is a very simple C++ application I made with QtCreator :

int main(int argc, char *argv[])
{
    int a = 1;
    int b = 2;

    if (a < 1 or b > 3)
    {
       return 1;
    }
    return 0;
}

To me, this is not valid C++, as the keyword or is not a reserved keyword.

But if I compile and run it, it works fine without any warnings ! The exit code is 0 and if I change b = 4, the exit code is 1 !

I'm not including anything to make sure there is no hidden define.

This is really strange to me. Is this something Qt is defining ? I didn't find anything in the documentation regarding that.

Answer

Thomas Owens picture Thomas Owens · Sep 16, 2009

According to Wikipedia:

C++ defines keywords to act as aliases for a number of symbols that function as operators: and (&&), bitand (&), and_eq (&=), or (||), bitor (|), or_eq (|=), xor (^), xor_eq (^=), not (!), not_eq (!=), compl (~).

As MadKeithV points out, these replacements came from C's iso646.h, and were included in ISO C++ as operator keywords. The Wikipedia article for iso646.h says that the reason for these keywords was indeed for international and other non-QWERTY keyboards that might not have had easy access to the symbols.

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