Sometimes you need to convert a long string to a null-terminated string, for example, if you are using a function that takes a PChar. If you must cast a string to a PChar, be aware that you are responsible for the lifetime of the resulting PChar. Because long strings are reference counted, typecasting a string to a PChar increases the dependency on the string by one, without actually incrementing the reference count. When the reference count hits zero, the string will be destroyed, even though there is an extra dependency on it. The cast PChar will also disappear, while the routine you passed it to may still be using it. For example:

procedure my_func(x: string);
begin
  // do something with x
  some_proc(PChar(x)); // cast the string to a PChar
  // you now need to guarantee that the string remains
  // as long as the some_proc procedure needs to use it
end;