C++向前聲明錯誤 - 左值cannont被綁定

Question

我有很多不同的向前聲明組合的發揮各地，這似乎是最好的之一。這是編譯只有一個，直到我註釋掉行

e->process(this); 

而且我從Xcode的一個錯誤，指出：

non-const lvalue reference to type 'Event::ModemSimV2' cannot bind to a temporary type 'ModemSimV2' 

我真的不明白是什麼意思，任何幫助將不勝感激。

感謝，

來源：

#include "ModemSimV2.h" 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//+++++++++++++++++++++++++++++ Event +++++++++++++++++++++++++++++ 

Event::Event(){ 

} 

Event::Event(const Event &e) { 
    *this = e; 
} 

Event::~Event() { 

} 

/* 
bool Event::operator > (const Event & rhs) const { 
    return time > rhs.time; 
} 

bool Event::operator < (const Event & rhs) const { 
    return time < rhs.time; 
} 

bool Event::operator <= (const Event & rhs) const { 
    return time < rhs.time; 
} 

bool Event::operator != (const Event & rhs) const { 
    return time != rhs.time; 
} 
*/ 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//+++++++++++++++++++++++++++++ Dialin +++++++++++++++++++++++++++++ 

Dialin::Dialin (int name, int tm) 
: time(tm), who(name) { 
    return; 
} 

Dialin::Dialin (const Dialin &d) { 
    *this = d; 
} 

Dialin::~Dialin() { 

} 

void Dialin::process(ModemSimV2 &m) { 


} 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//++++++++++++++++++++++++++ EventHeap ++++++++++++++++++++++++++++ 


EventHeap::EventHeap() { 

    size = 0; 
} 

EventHeap::EventHeap(int numVals) { 

    size = 0; 
} 

//insert 
void EventHeap::push(const Event e) { 

    *array[size] = e; 
    reIndex(size); 
    size++; 
} 

//removes the min val 
Event* EventHeap::pop() { 

    Event *e = array[0]; 
    array[0] = array[size - 1]; 
    size--; 
    if(!empty()) 
     buildHeap(0); 

    return e; 
} 

//re do 
void EventHeap::buildHeap(int nodeIndex) { 

    int leftChildIndex, rightChildIndex, minIndex; 
    Event *tmp; 

    leftChildIndex = getLeft(nodeIndex); 

    rightChildIndex = getRight(nodeIndex); 

    if (rightChildIndex >= size) { 

     if (leftChildIndex >= size) 

      return; 

     else 

      minIndex = leftChildIndex; 

    } else { 

     if (array[leftChildIndex] <= array[rightChildIndex]) 

      minIndex = leftChildIndex; 

     else 

      minIndex = rightChildIndex; 

    } 

    if (array[nodeIndex] > array[minIndex]) { 

     tmp = array[minIndex]; 

     array[minIndex] = array[nodeIndex]; 

     array[nodeIndex] = tmp; 

     buildHeap(minIndex); 

    } 
} 


//re index 
void EventHeap::reIndex(int hole) { 

    while(array[hole] != NULL && array[hole] < array[getParent(hole)]) { 
     int pIndex = getParent(hole); 
     Event *temp(array[hole]); 
     array[hole] = array[pIndex]; 
     array[pIndex] = temp; 
     hole = pIndex; 
    } 
} 

//is Empty 
bool EventHeap::empty() const { 
    return (size == 0); 
} 

int EventHeap::getLeft(int index) const { 
    return (index * 2) + 1; 
} 

int EventHeap::getRight(int index) const { 
    return (index * 2) + 2; 
} 

int EventHeap::getParent(int index) const { 
    return (index - 1)/2; 
} 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//++++++++++++++++++++++++++ ModemSimV2 +++++++++++++++++++++++++++ 

// Constructor for ModemSim. 
ModemSimV2::ModemSimV2(int modems, double avgLen, int callIntrvl, EventHeap e) 
: freeModems(modems), avgCallLen(avgLen), 
freqOfCalls(callIntrvl), r((int) time(0)) 
{ 
    eventSet = &e; 
    nextCall(freqOfCalls); // Schedule first call 
} 

// Place a new DIAL_IN event into the event queue. 
// Then advance the time when next DIAL_IN event will occur. 
// In practice, we would use a random number to set the time. 
void ModemSimV2::nextCall(int delta){ 
    static int nextCallTime = 0; 
    static int userNum = 0; 

    Event *e; 
    Dialin d = Dialin(userNum++, nextCallTime); 
    *e = d; 
    eventSet->push(*e); 
    nextCallTime += delta; 
} 

// Run the simulation until stopping time occurs. 
void ModemSimV2::runSim(int stoppingTime){ 
    Event *e; 

    while(!eventSet->empty()){ 
     e = eventSet->pop(); 
     if (e->getTime() > stoppingTime) 
      break; 
     e->process(this); 
     nextCall(freqOfCalls); 
    } 
} 

頁眉：

#ifndef MODEM_SIM_V2_H 
#define MODEM_SIM_V2_H 

#include <queue> 
#include <vector> 
#include <functional> // for greater() 
#include <climits>  // for INT_MAX 
#include <iostream> 
#include "random.h" 

using namespace std; 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//+++++++++++++++++++++++++++++ Event +++++++++++++++++++++++++++++ 

class Event{ 

protected: 
    int who;  // the number of the user 
    int time;  // when the event will occur 
    int what;  // DIAL_IN or HANGUP 
    class ModemSimV2; 

public: 
    Event(); 
    Event(const Event &e); 
    virtual ~Event(); 

    bool operator > (const Event & rhs) const; 
    bool operator < (const Event & rhs) const; 
    bool operator <= (const Event & rhs) const; 
    bool operator != (const Event & rhs) const; 

    int getTime() { return time; }; 

    virtual void process(ModemSimV2 &m) = 0; 
}; 


class Dialin : public Event{ 
public: 
    Dialin(int name = 0, int tm = 0); 
    Dialin(const Dialin &d); 
    ~Dialin(); 

    virtual void process(ModemSimV2 &m); 

private: 
    int who; 
    int time; 
    int what; 
}; 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//++++++++++++++++++++++++++ EventHeap ++++++++++++++++++++++++++++ 

class EventHeap{ 

public: 
    EventHeap(); 
    EventHeap(int numIndex); 

    bool empty() const; 
    const int & findMin() const; 

    void push(const Event x); 
    Event * pop(); 

private: 
    int size;   // Number of elements in heap 
    vector <Event*> array;   // The heap array 

    void buildHeap(int index); 
    void reIndex(int hole); 
    int getLeft(int index) const; 
    int getRight(int index)const; 
    int getParent(int index)const; 
}; 

//xvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvxvx 
//++++++++++++++++++++++++++ ModemSimV2 +++++++++++++++++++++++++++ 

class ModemSimV2{ 

public: 
    ModemSimV2(int modems, double avgLen, int callIntrvl, EventHeap e); 
    // Add a call to eventSet at the current time, 
    // and schedule one for delta in the future. 
    void nextCall(int delta); 

    // Run the simulation 
    void runSim(int stoppingTime);// = INT_MAX); 

    friend class Event; 

private: 
    Random r;      // A random source 
    EventHeap *eventSet;     // Pending events 

    // Basic parameters of the simulation 
    int freeModems;     // Number of modems unused 
    const double avgCallLen;  // Length of a call 
    const int freqOfCalls;   // Interval between calls 
}; 


#endif 

Answer 1

的問題是你把你向前聲明在錯誤的地方在頭中。該方法process認爲ModemSimV2屬於Event，因此在錯誤消息Event::ModemSimV2。將class ModemSimV2;移出受保護的部分，以達到課程之上。

class ModemSimV2; 

class Event 
{ 
    ... 

而且this是一個指向ModemSimV2，你將它傳遞給process之前必須取消對它的引用。

e->process(*this);