What does the vertical bar ( | ) mean in C++?

Question

I have this C++ code in one of my programming books:

WNDCLASSEX wndClass = { 0 };
wndClass.cbSize = sizeof(WNDCLASSEX);
wndClass.style =  CS_HREDRAW | CS_VREDRAW;

What does the single pipe do in C++ windows programming?

Bosket

This has nothing to do with windows programming; this is a basic operator of C++. – Theona

Actually it is a operator of C, C++ adopts it – Episode

Answer 1

Bitwise OR operator. It will set all bits true that are true in either of both values provided.

For example CS_HREDRAW could be 1 and CS_VREDRAW could be 2. Then it's very simple to check if they are set by using the bitwise AND operator &:

#define CS_HREDRAW 1
#define CS_VREDRAW 2
#define CS_ANOTHERSTYLE 4

unsigned int style = CS_HREDRAW | CS_VREDRAW;
if(style & CS_HREDRAW){
    /* CS_HREDRAW set */
}

if(style & CS_VREDRAW){
    /* CS_VREDRAW set */
}

if(style & CS_ANOTHERSTYLE){
    /* CS_ANOTHERSTYLE set */
}

See also:

• Wikipedia: Bitwise operation (Section OR)
• Wikipedia: Mask (computing) Section( Common bitmask functions)

Nonjoinder

whaa..? all bits to true? so let me think. 010101 | 101010 would return 111111? – Bosket

Yes. b00010101 | b00101010 will return b00111111. – Nonjoinder

Answer 2

In C++20, it can also be the pipe operator of range adaptor closure objects. I.e. chaining together operations on ranges. Read more about it here: https://en.cppreference.com/w/cpp/ranges#Range_adaptor_closure_objects

Monocular

github.com/ReactiveX/RxCpp check it out – Reedbuck

Answer 3

| is called bitwise OR operator.

|| is called logical OR operator.

Bifocals

Answer 4

It's a bitwise OR operator. For instance,

if( 1 | 2 == 3) {
    std::cout << "Woohoo!" << std::endl;
}

will print Woohoo!.

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