将迭代器与对象向量一起使用c ++

Question

i have class contains a ofstream file, i face problem when using iterator to delete an object of a vector of objects of this class.

Here is the error:

Error 10 error C2249: 'std::basic_ios<_Elem,_Traits>::operator =' : no accessible path to private member declared in virtual base 'std::basic_ios<_Elem,_Traits>' c:\\program files (x86)\\microsoft visual studio 10.0\\vc\\include\\ostream

Code:

static vector<VOIP> calls;
...
for(...)
{
    VOIP v = VOIP(...);
    calls.push_back(v);
}
...
for( int i = 0 ; i < calls.size() ; i++)
{
    if(...)
    {
        vector<VOIP>::iterator it = calls.begin() + i;
        calls.erase(it);//"?"
        break;
    }
}

Face Error C2249 raises from line "?", any help and this is the class

class VOIP
{
public:
    VOIP(string SourceDirectoryPath, string startTime, signalling sig, int callerIp[], int calleeIp[], int callerPort, int calleePort);
    VOIP(const VOIP & voip);
    ~VOIP(void);
    //caller and callee voice vectors 
    vector<u_char> callerVoiceVector;
    vector<u_char> calleeVoiceVector;
    //caller and callee voice files and path
    ofstream callerVoiceFile;
    ofstream calleeVoiceFile;   
    string outFilePath;
    string log;
    ofstream logFile;
    string startTime;
    string endTime;
    string length;
}

commented line in copy constructor raises the same error, ie Error C2249

VOIP::VOIP(const VOIP & voip)
    /*:calleePort(voip.calleePort), calleeVoiceFile(voip.calleeVoiceFile), calleeVoiceVector(voip.calleeVoiceVector),
     callerPort(voip.callerPort), callerVoiceFile(voip.callerVoiceFile), callerVoiceVector(voip.callerVoiceVector),
     callType(voip.callType), endTime(voip.endTime), length(voip.length), log(voip.log), logFile(voip.logFile),
     outFilePath(voip.outFilePath), startTime(voip.startTime),
     pleaseDial(voip.pleaseDial), DLHmm(voip.DLHmm)//signalings*///TODO
{
    cout<<"inside copy constractor"<<endl;
}

VOIP::~VOIP(void)
{
    callerVoiceVector.clear();
    calleeVoiceVector.clear();
    callerVoiceFile.close();
    calleeVoiceFile.close();
    logFile.close();
    cout<<"inside destractor"<<endl;
}

Answer 1

The standard library containers require, in general, that the objects they contain can be copy constructible and copy assignable. This is, they require access to the copy constructor (in your case, VOIP::VOIP(const VOIP&) ) and the copy assignment operator (in your case, VOIP::operator=(const VOIP&) ). If your class does not provide them explicitly, these functions are automatically generated by your compiler as long as it can do it: this is, as long as all class members are also copy constructible or copy assignable, which is not the case for VOIP , since ofstream cannot be copied.

Nevertheless, VOIP provides an explicit copy constructor, so no problems there. This is the reason why vector<VOIP>::push_back() , which needs the copy constructor, works. Unfortunately it does not provide a copy assignment operator and, strange as it seems, vector<VOIP>::erase() needs it. The reason is that, when you erase an element from the vector, all elements after it must be copied to the previous position in order to fill the gap. And this is what the error message is telling you: ofstream is not copyable because its base class std::basic_ios<> is not copyable, so VOIP is not copyable.

To solve your problem, you may provide a copy assignment operator for VOIP following the same ideas you used for the copy constructor. Incidentally, in C++ there is something called the rule of three : if a class has a explicit destructor, copy constructor or copy assignment operator, it usually needs all three of them. VOIP has the first two, but misses the third. Write it and everything will be fine.