c++ Segmentation fault in destructor child class - c++

Question

hi i am delevop a multicontainner using templates, but i am getting a segmentation fault from the child class destructor, here is the code:
#include <algorithm>
#include <map>
#include <iostream>
class BaseType{
public:
virtual ~BaseType(){}
virtual BaseType * clone() const =0;
};
template<typename T>
class DataType : public BaseType
{
public:
DataType(const T & aValueData = T()):mValue(aValueData) {
// new DataType<T>(*this)
}
~DataType(){
}
BaseType * clone() const
{
return new DataType<T>(*this);
}
T mValue;
};
class MValueData
{
public:
template<typename T>
MValueData(T const & aAnyValue = T()):mTypeData(0),isDelete(false)
{
std::cout<<"Object Address before create object: "<<mTypeData<<std::endl;
mTypeData=new DataType<T>(aAnyValue);
std::cout<<"Object Address after create object"<<mTypeData<<std::endl;
}
~MValueData(){
std::cout<<"Object Address "<<mTypeData<<std::endl;
delete mTypeData;
mTypeData=0;
}
MValueData()
{
mTypeData=0;
}
template<typename T>
MValueData(const MValueData & aCopy)
{
mTypeData= new DataType<T>();
*mTypeData=aCopy.mTypeData;
}
template<typename T>
const MValueData & operator=(const MValueData & aCopy)
{
mTypeData= new DataType<T>();
*mTypeData=aCopy.mTypeData;
//MValueData(aCopia).swap(*this);
}
void swap(MValueData& other) {
std::swap(this->mTypeData, other.mTypeData);
}
template <typename T>
T& get()
{
return dynamic_cast<DataType<T>&>(*this->mTypeData).mValue;
}
bool operator <(const MValueData &rhs) const {
return (mTypeData<rhs.mTypeData);
}
template<typename T>
void setValue(T const & anyValue=T())
{
mTypeData= new DataType<T>(anyValue);
}
BaseType *mTypeData;
private:
bool isDelete;
};
int main()
{
MValueData aAnyType_1(0.22);
aAnyType_1.get<double>();
MValueData aAnyType_2(false);
std::map<MValueData , MValueData&> mMapa;
mMapa.insert(std::pair<MValueData , MValueData&>(aAnyType_1,aAnyType_2));
// mMapa.find(aAnyType_1);
return 0;
}
I am using GDB to determinate the bug but i cannot see proper way to fix, the segmentacion stop when i comment this line:
~MValueData(){
// if(mTypeData) delete mTypeData;
}
Only then it run propperly, but it seems that i am creating a memory leak.
Updated:std::map create copys of the object that i insert into, the object is destroyed twice, one when exit the main function and another when std::map is destroying it self,
any hint?
thx in advance!

Answer 1

This segmentation fault might appear to be in the destructor, but it is a problem in your copy constructor. Lets take a simple example, I have a class which stores a pointer. Then I copy this pointer value like you are doing: I will have two pointers to the same memory location. Now I delete one of these objects, thus deleting the value at the pointer. The second object will have a pointer to invalid memory, and when this tries to delete the memory you get a segmentation fault.
How to fix this:
Well there are a few ways actually. Firstly, you need to decide whether you want deep copying of the pointers or not. If you do, write a deep copy of the memory the pointer points too. If not I reocmmend using shared_ptr to avoid these sorts of problems.

Answer 2

Your copy constructor is broken. You are not cloning the object, but only the pointer. Once an object is copied, the two copies will try to delete the same real object in memory in the destructor and that will cause a crash. You need to figure out who should own the object and whether you want it cloned or shared among the different instances of the MValueData object. Then act accordingly to fix the issue.

Answer 3

Your copy constructor is not correct.
It only copies the pointer not the object.
The two objects copied with the copy constructor will try to delete the same object in their destructor.