printf and custom class

Question

I have my own class that represents a custom string class. I\'m using VS2012RC. I have overloaded some operators of my class CustomString.

Here\'s some code:

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Answer 1

You can't (at least not in a portable way). printf looks at the object passed as parameter and treats it as a %s, which is a char array. You run into undefined behavior. Also, the parameters passed to printf are, sort of say, type-less.

Why printf(str) is ok?

Because the first parameter is types, and is a const char*. The implicit cast is made via your operator. The rest of the parameters don't behave the same.

I'd use cout instead, and overload operator << (ostream&, const CustomString&).

Don't do this:

I said you can't, in a portable way. For a class like

class CustomString
{
   char* str;
   //...
};

that might work, because of how classes are represented in memory. But, again, it's still undefined behavior.