String concat using overloaded operators.

[0x4B47]

Hi fellow coders,

Consider the class,

class String
{
public:
	String( const char* = "" );
	String( const String & );
	~String();

	const String& operator=( const String & );
    const String& operator+( const String & ); 
private:
	int length;
	char* pStr;
	void setString( const char* );	// Utility function
};

The problem is, how do I implement operator+ so that I can do this:

void main()
{
   String obj1, obj2("Hello"), obj3(" World");
   obj1 = obj2 + obj3;
   cout << obj1; // Should be "Hello World"
   cout << obj2; // Should be "Hello"
   cout << obj3; // Should be " World"
}

Without modifying obj2 or obj3?

Things you can assume:
- setString dynamically allocates memory for string passed through the constructor, ie pStr = new char blah blah
- ostream overloaded for stream extraction with String objects.

Please help me out.
Thanks in advance.

 

[PerFnurt]

Well since you pass the operator const String & I'd assume you cant modify them as of today...

// Note: Not returning a ref, but a new object.
String operator+( const String & other)
{
  std::string s = std::string(pStr)+std::string(other.pStr);

  return String(s.c_str());
}

/Per
[sub]
"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."[/sub]

 

[ArkM]

Some addition: don't declare your assignment op return value (ref to this) as const. You modify it by assignment - what for const now?..

 

[0x4B47]

Is it ok for me to do this:

String operator+( const String & other)
{
  length = this->length + other.length;
  const char* s = this->(pStr-1) + other.pStr;
  setString(s);
  return *this;
}

KG

01001011 01000111

 

[0x4B47]

oh no I can't do that because 'this' refers to the String object left of the operator doesn't it?
I'm sorry, I'm not in front of a compiler right now thats why I posted the above before giving it a try first. I've been thinking about it all day and this forum is the only thing I can access to maybe share my thoughts with.
How about:

String operator+( const String & other)
{
  const char* s = this->(pStr-1) + other.pStr;
  String concatStr(s);  
  return concatStr;
}

KG

01001011 01000111

 

[PerFnurt]

const char* s = this->(pStr-1) + other.pStr;

This is not string concatenation! It is some odd addition of pointers. Use strcat to concat. strings.

Assuming you have some utility method to given a length allocate the pStr:

String operator+( const String & other)
{
  String result;
  result.allocate(length+other.length); // Alloc enough for 'this'+other
  strcpy(result.pStr, pStr); // result='this'
  strcat(result.pStr, other.pStr); // result+=other
  return result;
}

/Per
[sub]
"It was a work of art, flawless, sublime. A triumph equaled only by its monumental failure."[/sub]