在C ++中，有一个名为

In C++, there is a concept called name hiding. Basically, a function or class name is "hidden" if there is a function/class of the same name in a nested scope. This prevents the compiler from "seeing" the hidden name.

C ++标准的3.3.7节内容为:

Section 3.3.7 of the C++ standard reads:

名称可以由显式隐藏 在一个同名的声明中 嵌套的声明性区域或派生 课(10.2)

A name can be hidden by an explicit declaration of that same name in a nested declarative region or derived class (10.2)

因此，要回答您的问题:在您的示例中，void foo(double a);被void bar_space::foo(Bar a);隐藏了 .因此，您需要使用::作用域确定运算符来调用外部函数.

So, to answer your question: in your example void foo(double a); is hidden by void bar_space::foo(Bar a); So you need to use the :: scoping operator to invoke the outer function.