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Thinking in C++
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Nested and local classes

You can easily put static data members in classes that are nested inside other classes. The definition of such members is an intuitive and obvious extension – you simply use another level of scope resolution. However, you cannot have static data members inside local classes (a local class is a class defined inside a function). Thus,

//: C10:Local.cpp
// Static members & local classes
#include <iostream>
using namespace std;

// Nested class CAN have static data members:
class Outer {
  class Inner {
    static int i; // OK

int Outer::Inner::i = 47;

// Local class cannot have static data members:
void f() {
  class Local {
//! static int i;  // Error
    // (How would you define i?)
  } x;

int main() { Outer x; f(); } ///:~

You can see the immediate problem with a static member in a local class: How do you describe the data member at file scope in order to define it? In practice, local classes are used very rarely.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire