设计模式——状态模式（C++实现）

 /////////context.cpp
 #include "context.h"

 void STContext::ChangeState(STState* pstState)
 {
         m_pstState = pstState;
 }

 void STContext::request()
 {
         m_pstState->Handle(this);
 }
 /////////// context.h
 #ifndef _CONTEXT_H_
 #define _CONTEXT_H_

 #include <iostream>
 #include <string>

 #include "state.h"

 using namespace std;

 class STState;

 class STContext
 {
 public:
         void ChangeState(STState* pstState);
         void request();

         STState* m_pstState;
 };

 #endif

 ///////////////////////////// state.cpp
 #include "state.h"

 void STConcreteStateA::Handle(STContext* pstContext)
 {
         cout<< "doing something in State A.\ndone, change state to State B"<< endl;
         pstContext->ChangeState(new STConcreteStateB());
 }

 void STConcreteStateB::Handle(STContext* pstContext)
 {
         cout<< "doing something in State B.\ndone, change state to State C"<< endl;
         pstContext->ChangeState(new STConcreteStateC());
 }

 void STConcreteStateC::Handle(STContext* pstContext)
 {
         cout<< "doing something in State C.\ndone."<< endl;
 }

 /////////////////////////////// state.h
 #ifndef _STATE_H_
 #define _STATE_H_
 #include <iostream>
 #include <string>

 #include "context.h"

 using namespace std;

 class STContext;

 class STState
 {
 public:
         virtual void Handle(STContext*) = ;
 };

 class STConcreteStateA: public STState
 {
 public:
         virtual void Handle(STContext* pstContext);
 };

 class STConcreteStateB: public STState
 {
 public:
         virtual void Handle(STContext* pstContext);
 };

 class STConcreteStateC: public STState
 {
 public:
         virtual void Handle(STContext* pstContext);
 };

 #endif

 ////////////////////// main.cpp
 #include <iostream>
 #include <string>

 #include "state.h"
 #include "context.h"

 using namespace std;

 int main(int argc, char* argv[])
 {
         STContext* pstContext = new STContext();

         STState* pstStateA = new STConcreteStateA();

         pstContext->ChangeState(pstStateA);
         pstContext->request();
         pstContext->request();

         return ;
 }

 /////////////////////
 [wenchaozeng@devnet_10_10_tlinux_64 ~/learn_code/design_pattern/13_state]$ ./main
 doing something in State A.
 done, change state to State B
 doing something in State B.
 done, change state to State C