What do two colons mean in C language?

The meaning of two colons (::) in C language: Scope resolution operator: resolves names in the scope, allowing access to names outside the current scope. Nested type name: Specify the name of the nested type, used to refer to the nested type.

The meaning of two colons in C language

In C language, the double colon (::) has the following meaning Two meanings:

1. Scope resolution operator

Double colon is used to resolve names in the scope. It allows access to names outside the current scope. For example:

<code class="c">int main() {
  int x = 10;
  {
    int x = 20;
    cout << ::x; // 输出 10
  }
  return 0;
}</code>

In the inner scope, the x variable declared in the outer scope is accessed through ::x.

2. Nested type name

Double colon is used to specify the name of the nested type. For example:

<code class="c">namespace myNamespace {
  class MyClass {
    struct InnerClass {
      // ...
    };
  };
}</code>

To refer to a nested type, use a double colon:

<code class="c">myNamespace::MyClass::InnerClass innerObject;</code>

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