我在下面的代码中得到链接器错误。如果我将ClientInterface的ClientAPI()函数设置为纯虚函数,那么链接器错误就会消失。这种行为的原因是什么?
// How the interface looks like to the Client
class ClientInterface
{
public:
virtual void ClientAPI();
virtual ~ClientInterface(){}
};
template <class TYPE> //this adaptor class can adapt to any type of legacy application as it is a generic function that uses template parameter to point to any legacy application
class Adaptor : public ClientInterface
{
public:
Adaptor(TYPE *objPtr, void (TYPE:: *fnPtr)())
{
m_objPtr = objPtr;
m_fnPtr = fnPtr;
}
void ClientAPI()
{
/*....
Do the conversion logic reqd to convert the user params into the params expected by your original legacy application...
....*/
(m_objPtr->*m_fnPtr)(); //Would call the method of the legacy application internally
}
~Adaptor()
{
if(m_objPtr)
delete m_objPtr;
}
private:
TYPE *m_objPtr; //You can keep either pointer to the Legacy implementation or derive the Legacy implementation privately by your Adaptor class
void (TYPE:: *m_fnPtr)();
};
//Adaptee classes below..
class LegacyApp1
{
public:
void DoThis()
{
cout<<"Adaptee1 API"<<endl;
}
};
//定义了main的执行类,并且包含了" adapter .h"
#include "headers.h"
#include "Adaptor.h"
void Adapter()
{
ClientInterface **interface_ptr = new ClientInterface *[2];
interface_ptr[0] = new Adaptor<LegacyApp1>(new LegacyApp1() , &LegacyApp1::DoThis);
interface_ptr[1] = new Adaptor<LegacyApp2>(new LegacyApp2() , &LegacyApp2::DoThat);
for(int i = 0; i < 2 ; i++)
{
interface_ptr[i]->ClientAPI();
}
}
int main()
{
//Testing();
Adapter();
char ch;
cin>>ch;
return 0;
}
因此上述代码中的更正如下:只需对原始代码的前几行进行以下更改。
// How the interface looks like to the Client
class ClientInterface
{
public:
//earlier I forgot to define it, so it was giving linker error as the function is just declared but not defined.
virtual void ClientAPI(){}
virtual ~ClientInterface(){}
};
谢谢。