How to use assignment operator on proxy of index operator - c++

Question

In the following code I made a template class, Its initialized in main function and I'm trying to assign char* as you can see below but It isn't working. I think the issue is in assign operator function I defined in Proxy class but I can't figure it out
#include <iostream>
using namespace std;
template <class T>
class Vector {
public:
T *p;
Vector(int size) {
p = new T[size];
}
class Proxy {
Vector &a;
int i;
public:
Proxy(Vector &a, int i) : a(a), i(i) {
}
void operator=(const T x) {
a.p[i] = x;
}
};
Proxy operator[](int i) {
return Proxy(*this, i);
}
};
int main() {
Vector<char *> sv1(2);
sv1[0] = "John";
sv1[1] = "Doe";
}
I'm getting following error;
I already tried setting parameter in assignment operator function to const, I also tried implicitly typecasting to T nothing has worked

Answer 1

Try this:
using namespace std;
template <class T>
class Vector {
public:
T* p;
int sz;
Vector(int size) {
p = new T[size];
sz = size;
}
template<class T>
class Proxy {
Vector<T>& v;
int i;
public:
Proxy(Vector<T>& vec, int index) :v(vec),i(index) { }
void operator= (const T val) { v.p[i] = val; }
};
Proxy<T> operator[](int index) { return Proxy<T>(*this, index); }
};
Your code will work with any basic type, (int, char, double) and pointers, but not, for example, with this:
int main() {
Vector<char*> sv1(2);
sv1[0] = "John";
sv1[1] = "Doe";
}
Firstly, the Vector points to a char*, not a string literal (const char*). You'd have to cast it using a C-style cast or a const_cast. Example:
int main() {
Vector<char*> sv1(2);
sv1[0] = const_cast<char*>("John"); //succeeds
sv1[1] = (char*)"Doe"; //succeeds
sv1[0] = "John"; //fails
sv1[1] = "Doe"; //fails
}
A string literal is always a const char* in C++.

Answer 2

You'll have same error writing code:
char * whatever = "something";
This code is absolutely wrong at least for string:
void operator=(const T x)
{
a.p[i] = x;
}
Step 1: allocate buffer;
Step 2: copy string to allocated buffer.
Your code is OK for primitives like char, int, etc. The following code should work:
int main() {
Vector<char> sv1(2);
sv1[0] = 'J';
sv1[1] = 'D';
}