Noob question.

The problem is probably in one of your strlen() calls. strlen() uses the null terminator to determine string length. However, you call strlen() on strings you haven't added the null terminator to in order to figure out where to put the null terminator. You'd probably be better off calling strlen() once in your constructors and store that length in a variable rather the repeatedly calling strlen().

Hmm, I will do that! And it's fixed! In the CFString::CFString(const CFString& str) function there's a strlen() on strdata, that should've been str.strdata Thanks anyway!

I have a question.
How does that printf(bla) in your main works?

I tested doing that here, but couldn't compile like that, since printf needs a format string.
printf's prototype is: int printf(const char *, ...)

Is that a typo? Or did you implement your own print function that receives a CFString object?
Just out of curiosity

His string class has a operator const char *() function which allows an implicit cast to const char *.

His string class has a operator const char *() function which allows an implicit cast to const char *.

But for the printf to work doesn't it need the "format string" and then the stuff you want to print?

Is this a safe thing to do?
g++ gave me some warnings at least..

It's legal code to have a format string come from a variable; however, it can be a security risk. The data in his string was a valid format string for being called with no other arguments because it didn't contain any %'s inside. However, if it had contained any %'s inside it, then it would have started reading information from the stack, which would be bad. Since the number of arguments printf() is called with is determined at compile time, and the format string could be changed at runtime, gcc will warn you about it.

Ah ok.
Thanks for clarifying that