🚀 go-pugleaf

The diagnostic exception classes are constructed from a const string&. Will
they copy the text or store a reference to the string?

-----
  19.1.1  Class logic_error                            [lib.logic.error]
 ...
  logic_error(const string& what_arg);

  Effects:
    Constructs an object of class logic_error.
  Postcondition:
    what() == what_arg.data().
-----      ??

Does this mean:

(1) class logic_error : public exception {
      string s;
    public:
      logic_error(const string& what_arg) :s(what_arg){}
      const char* what() const { return s.c_str(); }
    };
    post: strcmp( what(), what_arg.data() ) == 0
   
or does it mean:

(2) class logic_error : public exception {
      const string& s;
    public:
      logic_error(const string& what_arg) :s(what_arg){}
      const char* what() const { return s.data(); }
    };
    post: what() and what_arg.data() 
          shall point at the same memory location
   
Interpretation (1) implies that the exception object carries a copy of the
text. Then you can say throw runtime_error("error"); With (2) you must
construct diagnostic errors from global/static string objects.

  throw logic_error("error");  // is this wrong?

  static string text("error");
  throw logic_error(text);     // is this required?

--
Lars Farm, lars.farm@nts.mh.se

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