TITLE: function versus variable declarations


PROBLEM: [unknown author]

ofstream outfile();

[...]

How would you declare a function that returns an oftsream by value,
takes no argument and is called `outfile'?

[...]


RESPONSE: esap@cs.tut.fi (Pulkkinen Esa)

ofstream outfile(void); 

I've made this error many times. The confusion is mainly due to
the constructor call syntax - they look too much like "unnamed" declarations:

   declaration                   constructor call for unnamed object

(1)  string a("foo");            string("foo")
(2)  string a();                 ???
(3)  string a;                   string()

It's very easy to think that because in (1) the declaration and conversion
look similar, it would also in (2) and (3).


RESPONSE: kanze@gabi-soft.fr (J. Kanze), 22 Feb 96

It's worse that that:

    string          a( "foo" ) ;
        //  Declaration of a variable a, type string, init'ed with "foo"
    string          a() ;
        //  Declaration of a function a, no args, returning string
    char            arr[] = "foo" ;
    string          a( string( arr ) ) ;
        //  Declaration of a function a, 1 arg of type string, returning
        //  string!! 

I've never had any problem with the second form; just don't use
unnecessary parentheses.  On the other hand, I've yet to meet anyone
with a little experience who hasn't been bitten by the last.  To avoid
it:

    string          a = string( arr ) ;
        //  No good if string doesn't have a copy constructor
    string          a( (string)( arr ) ) ;
    string          a( static_cast< string >( arr ) ) ;

I generally prefer the second, and have adapted the rule of
systematically putting the type name in parentheses for explicit
constructor calls with one argument.  The first is fine in this case,
but typically, the problem hits you in more complicated cases, and
sometimes, the object being constructed will not have an accessible copy
constructor, making the = form of initialization illegal.