Static and Inline in C++

#programming #cpp

static and inline within classes

• static variables in a class make them shared across all instances of that class.

• static variables are declared inside the class but defined separately.
  The line static int x; only tells the compiler that such a variable exists somewhere, but no storage is yet allocated.
  Using it before definition leads to a linker error — “undefined reference to x” — meaning that while the compiler knows the name, no memory exists for it.

  • The strength of static is persistence. A static variable inside a function retains its value between calls; it isn’t destroyed when the function exits.
  • A static member function can be called without creating an object. It can only access other static members of the class.
  • At global or namespace scope, marking a function static gives it internal linkage, restricting visibility to that translation unit.

• In the case of a resource loader like {cpp}loadTextures(), making it static allows it to be called independently of any object.
  A line like {cpp}Image gun_img = LoadImage(); inside that function would normally create a local variable.
  Declaring it as {cpp}inline static Image gun_img; makes it a single, persistent variable belonging to the class itself — not recreated on each call.

• The {cpp}inline keyword, especially since C++17, allows merging the declaration and definition of {cpp}static data members directly in the class.

  • It also tells the compiler and linker to relax the One Definition Rule (ODR): multiple identical definitions across translation units are fine, only one will be kept.