Agenda:
Inside struct/class
- Case 1: without “static”
- Case 2: with “static”
- Case 3: with “static” — better way to call static member
Outside struct/class
- Case 1: without “static”
- Case 2: with “static”
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“static” could has 2 different meaning corresponding to it’s context:
- inside struct/class
- outside struct/class
“static” inside struct/class
The “static” member will share memory with all the instance of the struct/class. No matter how many instances of struct/class are created, there is only one “static” member.
- If an instance changes the “static” member, this change can be see from all the instances.
Case 1: without “static”
Both e and e1 has their own member of x and y:
Case 2: with “static”
Even through we have 2 entities e and e1, they are pointing at the same x and y of Entity. Therefore we printed the same value.
Case 3: with “static” — better way to call static member
We usually use “Entity::x” to call the static variables, as if x and y are variables under a namespace “Entity”
⚠️ Note:
- static function also works in similar way
- static function CANNOT access non-static variable
“static” outside struct/class
The “static” member is internal and ONLY visible in it’s own translation unit(in most case also means it’s own *.cpp file).
- Linker doesn’t need to link it to other file, because there won’t be any other file using this “static” member
Case 1: without “static”
Following situation caused error due to the duplicated declaration of variable “s_Variable”
Case 2: with “static”
static variable is ONLY available in Static.cpp’s scope. Therefore the Linker won’t find any conflict.
