I am trying to store a pointer to a member function in a structure which will be used to call the function later in my program.
Something like this:
// abc.h
namespace XYZ {
typedef void func(const uint8_t *buf, int len);
struct holder
{
// other members
func * storePtr;
}
} // end of namespace
the other file as:
// pqr.h
#include abc.h
namespace XYZ {
class pqr {
// data members and other functions
void func1(const uint8_t *buffer, int length);
void func2(func *section);
void func3();
}
} // end of namespace
Now my cpp file needs to store instance of this func1 in my structure member storePtr
// app.cpp
#include pqr.h
void pqr::funct3()
{
// Do something
func2(func1);
}
void pqr::func2(func * section)
{
holder h;
h.storePtr = section;
}
But I am getting compilation error at line "func2(func1);" as
"error C3867: 'pqr::func1': function call missing argument list; use '&pqr::func1' to create a pointer to member"
I have used &pqr:: to define the scope but it also doesn't solve my problem and I am not able to understand what to do.
Pointers to member function are not the same thing as pointers to normal functions - have a look at the explanation and example here: http://msdn.microsoft.com/en-us/library/k8336763.aspx
Related
I'm trying to make a thread every time a call a function from a class, but i can't pass the function correctly:
file.h
#include <thread>
class Class
{
public:
Class(int a);
void ThreadBase(void (*func));
int CreateThread(void (*func));
};
file.cpp
#include <thread>
Class::Class(int a)
{
/**
* ...
*/
}
void Class:ThreadBase(void (*func))
{
while(1)
{
/**
* ...
*/
}
}
int Class:CreateThread(void (*func))
{
std::thread th(Class::ThreadBase, func);
}
Error:
error: reference to non-static member function must be called
CreateThread should call std::thread with a function and arguments for the function.
The problem is here:
std::thread th(Class::ThreadBase, func);
Class::ThreadBase is not a static function; so it can't be called directly. In this case; CreateThread should call the member function "ThreadBase" of 'this.'
# include "stdafx.h"
# include <iostream>
#include <ctype.h>
using namespace std;
class a
{
protected:
int d;
public:
virtual void assign(int A) = 0;
int get();
};
class b : a
{
char* n;
public:
b()
{
n=NULL;
}
virtual ~b()
{
delete n;
}
void assign(int A)
{
d=A;
}
void assignchar(char *c)
{
n=c;
}
int get()
{
return d;
}
char* getchart()
{
return n;
}
};
class c : b
{
b *pB;
int e;
public:
c()
{
pB=new b();
}
~c()
{
delete pB;
}
void assign(int A)
{
e=A;
pB->assign(A);
}
int get()
{
return e;
}
b* getp()
{
return pB;
}
};
int _tmain(int argc, _TCHAR* argv[])
{
c *pC=new c();
pC->assign(10);
b *p=pC->getp();
p->assignchar("a");
char *abc=p->getchart();
delete pC;
cout<<*abc<<endl;
getchar();
}
i'm a noob at c++ and was experimenting when i got to this point. I don't understand why i keep getting a memory corruption message from VS2010. I am trying to replicate a problem which is at a higher level by breaking it down into smaller bits, any help would be appreciated.
From a cursory glance, you are passing a static char array to AssignChar that cannot be deleted (ie when you type "A" into your code, its a special block of memory the compiler allocates for you).
You need to understand what assignment of a char* does (or any pointer to type). When you call n=c you are just assigning the pointer, the memory that pointer points to remains where it is. So, unless this is exactly what you meant to do, you will have 2 pointers pointing to the same block of memory.. and you need to decide which to delete (you can't delete it twice, that'd be bad).
My advice here is to start using C++, so no more char* types, use std::string instead. Using char* is C programming. Note that if you did use a std::string, and passed one to assignChars, it would copy as you expected (and there is no need to free std::string objects in your destructor, they handle all that for you).
The problem occurs when you're trying to delete pC.
When ~c() destructor calls ~b() destructor - you're trying to delete n;.
The problem is that after assignchar(), n points to a string literal which was given to it as an argument ("a").
That string is not dynamically allocated, and should not be freed, meaning you should either remove the 'delete n;' line, or give a dynamically-allocated string to assignchar() as an argument.
I am getting multiple, confusing errors when building this school assignment and am hoping for some direction on what might be the problem. I wouldn't normally write it like this, but I put everything into one file as I try to debug this. Using Visual Studios Express 2012. I'm getting over 30 errors when I build, so I'm sure there is something fundamental that I am simply overlooking. Just a suggestion please, not looking for anyone to do my homework. Thanks
#include "stdafx.h"
#include <Windows.h>
#include <iostream>
#include "MessageDisplayClass.h"
#include "LogMessageClass.h"
#include "TimerEventArgs.h"
using namespace System;
ref class CustomTimerClass
{
private:
static bool stopFlag = false;
// create instance of TimerEventArgs
TimerEventArgs^ timerEvent;
public:
CustomTimerClass(void)
{
}
delegate void CustomTimerClass::TimerAlarmHandler(/*Object^ sender, TimerEventArgs^ args*/);
event CustomTimerClass::TimerAlarmHandler^ OnTimerAlarm;
property bool StopFlag
{
bool get(void)
{
return stopFlag;
}
void set(bool b)
{
stopFlag = b;
}
}
void run()
{
Sleep(1000);
raiseTimerAlarm();
}
void OnStart()
{
// create instances of DisplayMessageClass and LogMessageClass classes
DisplayMessageClass^ messageDisplayer = gcnew DisplayMessageClass(this);
LogMessageClass^ messageLogger = gcnew LogMessageClass(this);
// display and log messages concerning this event
messageDisplayer->displayMessage(this, timerEvent);
messageLogger->logMessage(this, timerEvent);
}
void raiseTimerAlarm()
{
// create instance of TimerEventArgs and get time of instance creation
timerEvent = gcnew TimerEventArgs();
String^ eventTime = timerEvent->EventTime;
// tie this instance of CustomTimerClass to OnTimerAlarm event and start event
this->OnTimerAlarm += gcnew TimerAlarmHandler(this, &CustomTimerClass::OnStart);
OnTimerAlarm();
}
};
ref class MainProgram
{
int main(array<System::String ^> ^args)
{
CustomTimerClass^ timerClass = gcnew CustomTimerClass();
DisplayMessageClass^ messageClass = gcnew DisplayMessageClass();
LogMessageClass^ logerClass = gcnew LogMessageClass();
timerClass->run();
return 0;
}
};
At the point you're trying to use the various classes, the compiler doesn't know about them yet. Move your main() function to the end of the file. Or better, split your class definitions in their own header files and then include them in your main source file.
There are other related problems too. For example, you're trying to use the TimerEventArgs class before the compiler knows about it. So you need to move the class definition up. This is why it's best to have each class in its own header file, and then include it where needed. Though it's not strictly unnecessary, if you declare/define everything in the correct order.
Other than wrong order of declarations, it looks like the problem is that the compiler doesn't recognize the ^ bit, which suggests you're not compiling as C++/CLI. Righ-click the project in Solution Explorer and go to Configuration Properties -> General, and make sure that Common Language Runtime Support is set to Common Language Runtime Support (/clr).
For the benefit of anyone else (other newbies): As it turns out, my suspicion that the problem lay in the fact that some of the classes were "#including" each other was the problem. Using forward declarations, combined with having to create a separate class altogether to act as a variable storage handler was the solution to my problem.
Here are the two classes that were giving me the biggest problem, corrected to function correctly:
/*
CustomTimerClass.h
*/
#include "StdAfx.h"
#include "LogMessageClass.h"
#include "MessageDisplayClass.h"
#include "TimerEventArgs.h"
#include "Variables.h"
//ref class MessageDisplayClass;
//ref class Variables;
using namespace System;
ref class CustomTimerClass
{
private:
static bool stopFlag = false;
// create instance of TimerEventArgs
TimerEventArgs^ timerEvent;
// create instance of MessageDisplayClass and LogMessageClass
MessageDisplayClass^ messageDisplayer;
LogMessageClass^ messageLogger;
Variables^ flagVariable;
public:
CustomTimerClass(void)
{
}
delegate void CustomTimerClass::TimerAlarmHandler();
event CustomTimerClass::TimerAlarmHandler^ OnTimerAlarm;
property bool StopFlag
{
bool get(void)
{
return stopFlag;
}
void set(bool b)
{
stopFlag = flagVariable->Flag;
}
}
void run()
{
Sleep(1000);
raiseTimerAlarm();
}
void OnStart()
{
// create instances of DisplayMessageClass and LogMessageClass classes
messageDisplayer = gcnew MessageDisplayClass(this, flagVariable);
messageLogger = gcnew LogMessageClass(this);
// display and log messages concerning this event
messageDisplayer->displayMessage(this, timerEvent);
messageLogger->logMessage(this, timerEvent);
}
void raiseTimerAlarm()
{
// create instance of TimerEventArgs and get time of instance creation
timerEvent = gcnew TimerEventArgs();
String^ eventTime = timerEvent->EventTime;
// tie this instance of CustomTimerClass to OnTimerAlarm event and start event
this->OnTimerAlarm += gcnew TimerAlarmHandler(this, &CustomTimerClass::OnStart);
OnTimerAlarm();
}
};
/*
MessageDisplayClass serves to display a message that
represents the time at which the TimerEventArgs class is
instantiated. This time is returned through a function
of TimerEventArgs class.
*/
#pragma once
#include "stdafx.h"
#include <iostream>
#include "TimerEventArgs.h"
#include "Variables.h"
using namespace System;
ref class CustomTimerClass; // FORWARD DECLARATION HERE CAN
// ONLY BE USED FOR REFERENCE. CANNOT
// BE USED WHEN METHODS OF THE CLASS
// ARE CALLED
ref class MessageDisplayClass
{
private:
CustomTimerClass^ customTimerRef;
// Variables CLASS CREATED SOLELY TO ACT AS GO-BETWEEN BETWEEN
// MessageDisplayClass and CustomTimerClass
Variables^ variableRef;
static int counter;
public:
// constructor
MessageDisplayClass(CustomTimerClass^ CustomTimerClassInput, Variables^ variableReference)
{
customTimerRef = CustomTimerClassInput;
variableRef = gcnew Variables (CustomTimerClassInput);
}
void displayMessage(Object^ sender, TimerEventArgs^ timer)
{
counter ++;
if (counter > 0)
{
variableRef->Flag = true;
Console::WriteLine("Message: an event occured at time stamp: " + timer->EventTime);
}
}
};
//Block.h
#pragma once
class Block
{
public:
CRect pos;
int num;
public:
Block(void);
~Block(void);
};
//view class
public:
Block currentState[5]; // stores the current state of the blocks
void CpuzzleView::OnDraw(CDC* pDC)
{
CpuzzleDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
if (!pDoc)
return;
//draw the 4 blocks and put text into them
for(int i=0;i<4;i++)
{
pDC->Rectangle(currentState[i].pos);
// i'm getting an error for this line:
pDC->TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
}
pDC->TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
The error says that no instance of overloaded function CDC::TextOutW() matches the argument list . But the prototype for the function is:
CDC::TextOutW(int x, int y, const CString &str )
all i've done is that instead of the 2 points i've directly given the point object returned by CenterPoint() ... shouldn't it work?
That's because you didn't supplied arguments list correctly. Please read compiler error message carefully, it's usually helps to solve the problem.
TextOut(currentState[i].pos.CenterPoint(), currentState[i].num);
In this call you passed CPoint object and int. This is not correct, you need to pass int, int and CString (or const char* and int length).
To fix this you shall do something like this:
CString strState;
strState.Format("%d", currentState[i].num); // Or use atoi()/wtoi() functions
TextOut(currentState[i].pos.CenterPoint().x, currentState[i].pos.CenterPoint().x, strState);
I am using vc++(2010). I am trying to create a class for server side socket. Here is the header file
#include<winsock.h>
#include<string>
#include<iostream>
using namespace std;
class AcceptSocket
{
// static SOCKET s;
protected:
SOCKET acceptSocket;
public:
AcceptSocket(){};
void setSocket(SOCKET socket);
static void EstablishConnection(int portNo,string&);
static void closeConnection();
static void StartAccepting();
virtual void threadDeal();
static DWORD WINAPI MyThreadFunction(LPVOID lpParam);
};
SOCKET AcceptSocket::s;
and the corresponding source file
#include<NetWorking.h>
#include<string>
void AcceptSocket::setSocket(SOCKET s)
{
acceptSocket=s;
}
void AcceptSocket::EstablishConnection(int portno,string &failure)
{
WSAData w;
int error = WSAStartup(0x0202,&w);
if(error)
failure=failure+"\nWSAStartupFailure";
if(w.wVersion != 0x0202)
{
WSACleanup();
failure=failure+"\nVersion is different";
}
SOCKADDR_IN addr;
addr.sin_family=AF_INET;
addr.sin_port=htons(portno);
addr.sin_addr.s_addr=htonl(INADDR_ANY);
AcceptSocket::s=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(AcceptSocket::s == INVALID_SOCKET)
failure=failure+"\nsocket creating error";
if(bind(AcceptSocket::s,(LPSOCKADDR) &addr,sizeof(addr)) == SOCKET_ERROR)
failure=failure+"\nbinding error";
listen(AcceptSocket::s,SOMAXCONN);
}
void AcceptSocket::closeConnection()
{
if(AcceptSocket::s)
closesocket(AcceptSocket::s);
WSACleanup();
}
void AcceptSocket::StartAccepting()
{
sockaddr_in addrNew;
int size=sizeof(addrNew);
while(1)
{
SOCKET temp=accept(AcceptSocket::s,(sockaddr *)&addrNew,&size);
AcceptSocket * tempAcceptSocket=new AcceptSocket();
tempAcceptSocket->setSocket(temp);
DWORD threadId;
HANDLE thread=CreateThread(NULL,0,MyThreadFunction,(LPVOID)tempAcceptSocket,0,&threadId);
}
}
DWORD WINAPI AcceptSocket::MyThreadFunction(LPVOID lpParam)
{
AcceptSocket * acceptsocket=(AcceptSocket *) lpParam;
acceptsocket->threadDeal();
return 1;
}
void AcceptSocket::threadDeal()
{
"You didn't define threadDeal in the derived class";
}
Now the main.cpp is
#include<Networking.h>
int main()
{
}
When I am compiling the error I got is
Error 1 error LNK2005: "private: static unsigned int AcceptSocket::s" (?s#AcceptSocket##0IA) already defined in NetWorking.obj C:\Documents and Settings\prabhakaran\Desktop\check\check\main.obj check
Error 2 error LNK1169: one or more multiply defined symbols found C:\Documents and Settings\prabhakaran\Desktop\check\Debug\check.exe 1 1 check
What might cause this and how do I solve it?
Put this in your .cpp file instead of in your .h file:
SOCKET AcceptSocket::s;
It is being included in many .cpp files if you have it in your .h file. And hence when you link it doesn't know which one to use.
Maybe a #pragma once at the very beginning of your header file will solve the problem.
The error message tells you that the linker finds multiple definitions of your class, obviously because you are including the header more than once.
That is fine in general, but then you should always add some so called inclusion guards in your header file to prevent this error.
EDIT:
Just saw that Brian R. Bondys answer is the correct one.
I'd like to elaborate on what Frank said. It's a common assumption that include guards might solve these kind of errors. Since the explanation got a bit lengthy, I've made a blog-post about it to explain the details:
http://daniel-albuschat.blogspot.com/2010/08/what-include-guards-in-c-are-and-what.html
Hope this is useful.