Question

Simple question but what does the | operator do as opposed to the || (or) operator?

Answer 1

| is a bitwise OR operator, where as || is a logical OR operator. Namely, the former is used to “combine” the bits from two numeric values as a union, whereas the latter evaluates to true if either condition on the left or right side of the operator is true.

Specifically, bitwise operators (not to be confused with logical operators) operate on each bit of the numbers (at the same ordinal position), and calculates a result accordingly. In the case of a bitwise OR, the resulting bit is 1 if either bit is 1, and 0 only if both bits are 0. For example, 1|2 = 3, because:

1 = 0001
2 = 0010
--------
    0011 = 3

Furthermore, 2|3 = 3, because:

2 = 0010
3 = 0011
--------
    0011 = 3

This can seem confusing at first, but eventually you get the hang of it. Bitwise OR is used mostly in cases to set flags on a bit field. That is, a value holding the on/off state for a set of related conditions in a single value (usually a 32 bit number). In Win32, the window style value is a good example of a bit field, where each style is represented by a single bit (or flag), like WS_CAPTION, which indicates whether or not the window has a title bar.