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Thinking in C++
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Global scope resolution

The scope resolution operator gets you out of situations in which the name the compiler chooses by default (the “nearest” name) isn’t what you want. For example, suppose you have a structure with a local identifier a, and you want to select a global identifier a from inside a member function. The compiler would default to choosing the local one, so you must tell it to do otherwise. When you want to specify a global name using scope resolution, you use the operator with nothing in front of it. Here’s an example that shows global scope resolution for both a variable and a function:

//: C04:Scoperes.cpp
// Global scope resolution
int a;
void f() {}

struct S {
  int a;
  void f();

void S::f() {
  ::f();  // Would be recursive otherwise!
  ::a++;  // Select the global a
  a--;    // The a at struct scope
int main() { S s; f(); } ///:~

Without scope resolution in S::f( ), the compiler would default to selecting the member versions of f( ) and a.

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