c++ - 初始化在同一头文件中定义的底层的顶层类

Question

可能是个愚蠢的问题。我很抱歉，但我想做以下事情，

connectionState currentState;

class connectionState {
    public:
        .......
        .......
};

相当

class connectionState {
    public:
        .......
        .......
};

connectionState currentState;

前者根本不编译，而后者则编译。那么，没有办法做到这一点吗？

标签： c++classc++11namespaces

Answer 1

对此有前向声明。前向声明也解决了循环依赖的问题：

class connectionState; // forward class declaration
extern connectionState currentState; // forward global extern variable declaration, now possible because connectionState is declared as a typename/class name
static connectionState currentState; // forward global static variable declaration 

class connectionState { ... }; // implementation/definition, can access currentState
connectionState currentState = ...; // definition/initialization
connectionState currentState {...}; // definition/initialization