C++ Overloading operator +()

Question

I have a simple class called String which has as a private field a char*.

class String { char *s; + some public methods };

I want to overload the + operator so a + b would mean that the strings from a and b are concatenated.

The function is here:

String String::operator+(String a) { String rez; rez.s = new char[strlen(this->s) + strlen(a.s) + 1]; assert(rez.s); strcpy(rez.s, this->s); strcat(rez.s, a.s); cout<<rez.s<<endl; // HERE rez.s CONTAINS THE RIGHT STRING! return rez; }

After I call this: c = a + b;

i get an error called Debug assertion failed.

Any ideas?

What you are trying ot do is not constructor overloading, but operator overloading. — PaulG
– PaulG, Commented Nov 7, 2012 at 20:38
Also do 'a' and 'b' contain real strings? You may be calling strlen on NULL or uninitialized pointers. — KSchmidt
– KSchmidt, Commented Nov 7, 2012 at 20:41
If you're going to implement your own string class IMO you ought to at least make it 8-bit clean (i.e. not-null terminated). — Craig Wright
– Craig Wright, Commented Nov 7, 2012 at 20:43

WhozCraig · Accepted Answer · 2012-11-08 10:28:02Z

First, read up on the Rule of Three

Then, consider this:

class String { char *s; // << pointer + some public methods };

"+ some public methods" better have a constructor that initializes the pointer member to a testable value (like NULL) or you're well-into undefined behavior. It better override the copy-constructor and assignment operators to properly duplicate the string from one String object to another. Finally, it better have a destructor that knows how to clean up a dynamic pointer to the content allocated in all of the above.

I strongly suggest you read that article backwards and forwards.

I didn't have a copy constructor. In my function rez was exactly what I wanted but I was returning the pointer that was deleted by destructor at the end of the function. Thank you!

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