c++ - cpp hpp分离

Question

当我尝试将类的声明和定义放入单独的 hpp 和 cpp 文件时出现一些错误。你能帮我修一下吗？我正在尝试像这样操纵一个单例:

唱.hpp:

class GlobalClass {
    int m_value;
    static GlobalClass *s_instance;
    GlobalClass(int);

  public:
    int get_value();
    void set_value(int v);
    static GlobalClass *instance(); };

唱.cpp:

#include"sing.hpp"
GlobalClass::GlobalClass(int v = 0)
{
    this->m_value = v;
}

int GlobalClass::get_value()
{
    return this->m_value;
}

void GlobalClass::set_value(int v)
{
    this->m_value = v;
}

static GlobalClass GlobalClass::*instance()
{
    if (!s_instance)
        s_instance = new GlobalClass;
    return s_instance;
}

主要.cpp:

#include "sing.hpp"
int main()
{
    GlobalClass *s=0;
}

命令和错误是:

~/workspace/singleton$ g++  main.cpp sing.cpp 
sing.cpp: In function ‘GlobalClass GlobalClass::* instance()’:
sing.cpp:19:10: error: ‘s_instance’ was not declared in this scope
sing.cpp:2:1: error: ‘GlobalClass::GlobalClass(int)’ is private
sing.cpp:20:23: error: within this context
sing.cpp:21:12: error: ‘s_instance’ was not declared in this scope

Answer 1

static GlobalClass GlobalClass::*instance()
{
    if (!s_instance)
        s_instance = new GlobalClass;
    return s_instance;
}

这个定义不应该有 static 标签。只有声明。

事实上，您实际上并没有定义成员函数；如果您提供了一个 s_instance 变量，您将然后得到关于它的错误。

* 也放错地方了。

您稍后还会收到关于 s_instance 的链接错误，因为您没有定义它。