C++ - Accessing char* with &String[0] on class - c++

Question

I was just experimenting and making my own string class. (Mainly because there is some stuff I wanted to build in custom methods like "toBase64" etc. Anyways, I was wondering how you could access the private member of char* when you use &String[0].
I thought you could use operator-overloading but I currently only have it as String[0] returns the char*. (I know & is the pointer operator).
String.h
namespace CoffeeBeans
{
class _declspec(dllexport) Coffee_String
{
char* String;
int StringLength;
public:
Coffee_String();
Coffee_String(LPCSTR CString);
LPSTR operator[](int);
~Coffee_String();
};
}
String.cpp
#include "stdafx.h"
#include "String.h"
#include <Windows.h>
CoffeeBeans::Coffee_String::Coffee_String() {
this->String = nullptr;
this->StringLength = 0;
}
CoffeeBeans::Coffee_String::~Coffee_String() {
if (String != nullptr) {
delete[] this->String;
this->String = nullptr;
this->StringLength = 0;
}
}
CoffeeBeans::Coffee_String::Coffee_String(LPCSTR CString) {
int StringLength = strlen(CString) + 1;
this->String = new char[StringLength]();
this->StringLength = StringLength - 1;
memcpy_s(this->String, StringLength, CString, StringLength);
}
LPSTR CoffeeBeans::Coffee_String::operator[](int)
{
return this->String;
}
Main.cpp
case WM_CREATE:{
CoffeeBeans::Coffee_String String("Test");
//I want to be able to do
//strcpy_s(&String[0], 3, "hi"); //Copy "hi" into the private variable char*String.
//I know this isn't a practical use, I wanted quick example (I would really pass it to recv (WinSock2))
MessageBeep(0);
break;
}

Answer 1

Your operator[] is returning the wrong value. In order for &String[index] to access the correct memory address, operator[] needs to return a reference to the character at the specified index, not return the string pointer itself, as you are currently doing.
If you look at the actual declaration of std::string::operator[], you will see that it returns a std::string::reference (aka char &) or std::string::const_reference (aka const char &) (depending on whether it is being called on a non-const or const std::string object).
Try something more like this:
String.h
namespace CoffeeBeans
{
class _declspec(dllexport) Coffee_String
{
char* String;
int StringLength;
public:
Coffee_String();
Coffee_String(const Coffee_String &src);
Coffee_String(const char *src);
~Coffee_String();
char& operator[](int index);
const char& operator[](int index) const;
Coffee_String& operator=(const Coffee_String &rhs);
};
};
String.cpp
#include "stdafx.h"
#include "String.h"
#include <algorithm>
#include <cstring>
CoffeeBeans::Coffee_String::Coffee_String() {
String = nullptr;
StringLength = 0;
}
CoffeeBeans::Coffee_String::Coffee_String(const CoffeeBeans::Coffee_String &src) {
StringLength = src.StringLength;
String = new char[StringLength+1];
std::copy(src.String, src.String+StringLength, String);
String[StringLength] = 0;
}
CoffeeBeans::Coffee_String::Coffee_String(const char *src) {
StringLength = std::strlen(str);
String = new char[StringLength+1];
std::copy(src, src+StringLength, String);
String[StringLength] = 0;
}
CoffeeBeans::Coffee_String::~Coffee_String() {
delete[] String;
String = nullptr;
StringLength = 0;
}
char& CoffeeBeans::Coffee_String::operator[](int index)
{
return String[index];
}
const char& CoffeeBeans::Coffee_String::operator[](int index) const
{
return String[index];
}
CoffeeBeans::Coffee_String& CoffeeBeans::Coffee_String::operator=(const CoffeeBeans::Coffee_String &rhs);
{
Coffee_String temp(rhs);
std::swap(String, temp.String);
std::swap(StringLength, temp.String);
return *this;
}
Main.cpp
case WM_CREATE: {
CoffeeBeans::Coffee_String String("Test");
strcpy_s(&String[0], 3, "hi"); //Copy "hi" into the private variable char *String...
// note that the content of String will become "hi\0t\0", not "hi\0"
// and StringLength will still be 4...
MessageBeep(0);
break;
}