Segmentation Fault in memcpy operation of a struct - c++

Question

I am adding the header file and cpp file (it has main fucntion).
AuctionPrices.h
#ifndef AuctionPrices_h
#define AuctionPrices_h
/*
*
* class AuctionPrices - maintains Buy Order, Sell Order books
*/
#include <bits/stdc++.h>
#include <map>
//#pragma pack(1)
struct Order
{
char * itemId;
char * auctionId;
int Side;
};
class AuctionPrices
{
public:
virtual int AddNewOrder(char *itemId, char *auctionId, int Side, int Price) = 0;
virtual int DeleteOrder(char *itemId, char *auctionId) = 0;
virtual int Print() = 0;
};
class AuctionPrice_Imp : public AuctionPrices
{
public:
AuctionPrice_Imp();
~AuctionPrice_Imp();
std::map <int, Order, std::greater< int >> BuyMap;
std::map <int, Order, std::less< int >> SellMap;
int AddNewOrder(char *itemId, char *auctionId, int Side, int Price);
int DeleteOrder(char *itemId, char *auctionId);
int Print();
};
#endif
AuctionPrices_Imp.cpp
/**
* Auction Price Class implementation
* Constructor, AddNewOrder, DeleteOrder, Print
*
*/
#include <bits/stdc++.h>
#include <map>
#include "AuctionPrices.h"
using namespace std;
AuctionPrice_Imp::AuctionPrice_Imp()
{
}
AuctionPrice_Imp::~AuctionPrice_Imp()
{
}
int AuctionPrice_Imp::AddNewOrder(char *itemId, char *auctionId, int Side, int Price)
{
Order order;
memcpy(order.itemId, itemId, strlen(itemId)+1);
memcpy(order.auctionId, auctionId, strlen(auctionId)+1);
order.Side = Side;
if (Side == 1)
{
BuyMap.insert (std::pair<int,Order>(Price,order));
//buyLevels_.insert( std::pair< OfPrice, Level< OrderEntry > >( price, buyLevel ) );
}
else if (Side == 2)
{
SellMap.insert (std::pair<int,Order>(Price,order));
}
else
{
return 0;
}
return 1;
}
int AuctionPrice_Imp::DeleteOrder(char *itemId, char *auctionId)
{
return 0;
}
int AuctionPrice_Imp::Print()
{
std::map <int,Order,std::greater< int >>::iterator buy_it;
std::map <int,Order,std::less< int >>::iterator sell_it;
// Print Sell Map
for ( sell_it = SellMap.begin();sell_it != SellMap.end(); sell_it++)
{
std::cout << sell_it->first << '\t' << std::endl;
}
// Print Buy Map
for ( buy_it = BuyMap.begin();buy_it != BuyMap.end(); buy_it++)
{
std::cout << buy_it->first << '\t' << std::endl;
}
return 1;
}
int main()
{
AuctionPrice_Imp * auctionPrice_Imp = new AuctionPrice_Imp();
/*
AddNewOrder(“item1”, “auction1”, 1, 100)
AddNewOrder(“item1”, “auction2”, 1, 101)
AddNewOrder(“item2”, “order3”, 1, 99)
AddNewOrder(“item2”, “order4”, 2, 100)
*/
auctionPrice_Imp->AddNewOrder("item1", "auction1", 1, 100);
auctionPrice_Imp->AddNewOrder("item1", "auction2", 1, 101);
auctionPrice_Imp->AddNewOrder("item2", "order3", 1, 99);
auctionPrice_Imp->AddNewOrder("item2", "order4", 2, 100);
auctionPrice_Imp->Print();
}
When I am running the code its giving segmentation fault at the line:
memcpy(order.auctionId, auctionId, strlen(auctionId)+1);
Please anyone can help or correct the code.
The functions I am calling are supposed to add the orders to the Maps: BuyMap and SellMap. Once they have added to those map, I am using a print function to print the values.

Answer 1

Order order;
This creates a new Order object. Order does not have a constructor, so none of its class members, itemId, and auctionId, get initialized to point to anything. These pointers are uninitialized, random garbage. Immediately afterwards:
memcpy(order.itemId, itemId, strlen(itemId)+1);
memcpy(order.auctionId, auctionId, strlen(auctionId)+1);
Since neither itemId, nor auctionId, point to sufficient memory that are at least strlen(itemId)+1 or strlen(auctionId)+1 in size, respectively, this results in undefined behavior, and your crash.
In C++, before using a pointer, it is your responsibility to make sure that the pointer is valid, and points to the correct object, objects, or sufficiently-sized memory buffers. C++ will not do that for you, you have to do all that work yourself.
But if your intent is to write modern C++ code, it is much simpler just to use C++ classes, like std::strings instead of plain char * pointers. std::strings automatically handle all these low-level details, manage memory properly, without making it your responsibility to do so. You will find a complete description of std::string and many examples of using it in your C++ textbook.

Answer 2

You should use std::string to avoid having to deal with low level issues of pointers and memory allocation. These are the issues that you are getting wrong in your code. Here's your code rewritten to use std::string
struct Order
{
std::string itemId;
std::string auctionId;
int Side;
};
int AuctionPrice_Imp::AddNewOrder(std::string itemId, std::string auctionId, int Side, int Price)
{
Order order;
order.itemId = itemId;
order.auctionId = auctionId;
order.Side = Side;
See how easy that is? The code to use std::string is no different to the code that handles int.