Re: Default conversion when passing to an ellipsis

From:
"Bo Persson" <bop@gmb.dk>
Newsgroups:
comp.lang.c++
Date:
Thu, 22 Jun 2006 23:56:18 +0200
Message-ID:
<4g0i02F1k6jn5U1@individual.net>
"Kufa" <potages@gmail.com> skrev i meddelandet
news:1151008878.265596.308030@i40g2000cwc.googlegroups.com...

Hi,

I have a class String which implements the const char*() operator. I
was doing some tests today and did something like:
String test( "hello world" );
printf( "%s\n", test ); // instead of test.c_str(); or (const
char*)test

This code compiled and worked fine on a x86/visual studio 7.1. On
some
other platforms, gcc was giving errors, as i would expect.

So i'm wondering if visual studio is allowing something which is
forbidden by the standard, or is there a way to force a default
conversion operator to be called when an object instance is passed
to
an ellipsis?


You are not allowed to pass a class object thru an ellipsis. If you
do, the compiler is allowed to do whatever it likes.

The CString class in VS7.1 does its trick by having the class object
contain a char* pointer only. That way printf cannot tell the
difference between a raw pointer and a class containing the pointer!

Bo Persson

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