Difference between "or" and "||"

Question

Is there any difference between

if ( a or b or c ) {

...and...

if ( a || b || c ) {

...and more in general between the two operators, even in terms of precedence ?

Answer 1

Aside from the stylistic sense that makes a lot of seasoned programmers think "Huh, has someone suddenly started writing Pascal?", there is no functional difference.

The purpose of these alternative names is to allow people living in, say, Sweden or Germany, to use a standard Local variant of ASCII, where | is ö.

Since the introduction of Unicode and extended ASCII, this need has pretty much disappeared, since nationalized character sets don't have to "steal" less commonly used characters to produce their national "special" characters.

Answer 2

edited You can overload operator or.

They are the same.

See Operators in C and C++.

If you overload operator or for a type, you can't then overload operator|| for the same type as the compiler will consider them to be the same function.

This error comes from the following code:

> prog.cpp: In function ‘bool operator||(Type, Type)’:
> prog.cpp:8:6: error: redefinition of ‘bool operator||(Type, Type)’
> prog.cpp:4:6: error: ‘bool operator||(Type, Type)’ previously defined here

On ideaone:

class Type {}
};

bool operator or(Type lhs, Type rhs) {
    return true;
}

bool operator ||(Type lhs, Type rhs) {
    return false;
}

int main() {
    Type a;
    Type b;
    a or b;
    a || b;
}

Answer 3

As per ISO14882:2011(e) 2.6-2 (Table 2) or is an alternative token for ||, and as such has exactly the same meaning:

In all respects of the language, each alternative token behaves the same, respectively, as its primary token,except for its spelling.

Often compilers implement them as #define or || or the internal equivalent.

Same for and, bitor, xor, compl, bitand, and_eq, or_eq, xor_eq, not and not_eq.

Answer 4

As was said in the other answers, the two are meant to be the same and thus exchangeable. But there is one big difference: MSVC, C++ Builder and maybe other compilers as well do not support or without including a special header. That makes using or a portability obstacle.