what does it mean by type = 1 << 0? [duplicate]

Question

everyone. When learning OC recently, I always come across enum like this.

enum {
    type1  = 0,
    type2  = 1 << 0,
    type3  = 1 << 1,
};

What does it mean by type = 1 << 0 ? What is it usually used for? Thanks in forward.

Answer 1

Bitwise Shift Left Operator

In Objective-C the bitwise left shift operator is represented by the '<<' sequence, followed by the number of bit positions to be shifted

Source

Also read this famous post to understand what it does and how

Answer 2

<< is binary operator

1 << 0 = 1
1 << 1 = 2
1 << 2 = 4

Answer 3

This operator is a bitwise shift (not only in objective-c).

you can assign every entry in an enum an integervalue, so it is the same as

enum {
    type1  = 0,
    type2  = 1,
    type3  = 2
};

you can use the shift-operator to easily assure that your enum entries can be bitwise added like

int bitmask = type2 | type3 //bitmask = 3

Answer 4

It is one bit shift. Such a construction could be used if you need to assign several types to something. It's called bit mask. Example:

enum {
    type1  = 1,
    type2  = 1 << 1,
    type3  = 1 << 2,
};

Means that type1 is binary 00000001, type2 is 00000010, type3 is 00000100 and so on. So, if type mask is 3 (00000011) you know that your object is type1 and type2.