How to fix the error in C++ vector operation? - c++

Question

The f() function in the class MapSquare works properly.. When I add the other class MapTriple, it is not working. f() function in the MapSquare should find the square of the elements in the vector and in the MapTriple should multiply 3 to all elements.
MapGeneric is the base class which contains the function map() which is a recursive function to access the vector elements and the f() function is a pure virtual function.
MapSquare and MapTriple are two derived classes overrides the f() function to find the square of vector elements and to multiply 3 with all the vector elements.
MapSquare works properly... but when I add MapTriple, segmentation fault occures. Please help to solve this.
#include<vector>
#include<iostream>
#include<cstdlib>
#include<stdio.h>
#include<stdlib.h>
using namespace std;
class MapGeneric
{
public:
virtual int f(int){};
vector<int> map(vector<int>, int);
};
class MapSquare:public MapGeneric
{
public: int f(int);
};
class MapTriple:public MapGeneric
{
public: int f(int);
};
class MapAbsolute:public MapGeneric
{
public: int f(int);
};
vector<int> MapGeneric::map(vector<int> v, int index)
{
if(index>=1)
{
v[index]=f(v[index]);
return map(v,index-1);
}
return v;
}
int MapSquare::f(int x)
{
return x*x;
}
int MapTriple::f(int x)
{
return 3*x;
}
int MapAbsolute::f(int x)
{
return abs(x);
}
int main()
{
//mapping square
MapSquare ob;
vector<int> L,L1,L2;
for (int i = 1; i <= 5; i++)
L.push_back(i);
L1=ob.map(L,sizeof(L));
cout<<"Square = ";
for ( vector<int>::iterator i = L1.begin(); i != L1.end(); ++i)
cout << *i<<" ";
//mapping triple
MapTriple t;
L2=t.map(L,sizeof(L));
cout<<endl<<"Triple = ";
for(vector<int>::iterator i=L2.begin();i!=L2.end();++i)
cout<<*i<<" ";
return 0;
}

Answer 1

A number of problems here. It looks as though you think that C++ indices start at 1, rather than zero?
if(index>=1)
{
v[index]=f(v[index]);
return map(v,index-1);
}
To me that immediately looks wrong, surely you mean:
// use size_t for indices (which cannot be negative)
vector<int> MapGeneric::map(vector<int> v, size_t index)
{
// make sure the index is valid!
if(index < v.size())
{
v[index] = f(v[index]);
return map(v, index - 1);
}
return v;
}
Secondly, the sizeof() operator does not do what you expect!! It returns the size of std::vector (which is usually 24bytes on 64 bit systems - basically 3 pointers). You should use the size() method to determine the length of the array.
// remember that indices are zero based, and not 1 based!
L1=ob.map(L, L.size() - 1);