VC to C++ Builder code conversion

I am trying to convert some code from VC to C++ Builder 5 pro.

For the line:
operator string() const;
I get these errors:
Error E2076 .\strtok.h 32: Overloadable operator expected
Error E2040 .\strtok.h 32: Declaration terminated incorrectly

Farther down in the implementation:
inline StrTok::operator string() const
{
  if (curToken)
      return string(curToken,curTokenLength);
  return string("");
}
I get these errors:
Error E2076 .\strtok.h 59: Overloadable operator expected
Error E2040 .\strtok.h 59: Declaration terminated incorrectly

This is a small and relatively uncomplicated class, but I am stuck on what the Borland C++ Builder compiler is looking for.

What should I replace these with?
I tried AnsiString(), but it gave the exact same errors.