Re: enum promote to bool type rather than Integer type?

From:

Michael Doubez <michael.doubez@free.fr>

Newsgroups:

comp.lang.c++

Date:

Tue, 4 Aug 2009 00:05:45 -0700 (PDT)

Message-ID:

<56abe8d4-e2dc-4fb0-b5bd-9304d555c2df@k6g2000yqn.googlegroups.com>

On 4 ao=FBt, 05:14, FireEmissary <blood_...@sina.com.cn> wrote:

I get it!

enum
{
        TIXML_SUCCESS,
        TIXML_NO_ATTRIBUTE,
        TIXML_WRONG_TYPE

};

#define EXCEPTION_PARSER(T) do{if(!T)throw InnateException();}while
(0)

int retcode=todoElement->QueryIntAttribute
("active_per_lay",&ActivedNumPerLay);
        EXCEPTION_PARSER(retcode==TIXML_SUCCESS);

I forget In brackets. so EXCEPTION_PARSER
(retcode==TIXML_SUCCESS);expand to

do ({if(!TIXML_SUCCESS==retcode)throw InnateException();}while(0)

must to be EXCEPTION_PARSER((retcode==TIXML_SUCCESS));

It is a matter of operator precedence: operator ! has more precedence
than operator ==, which mean that :
!TIXML_SUCCESS==retcode
is interpreted as
(!TIXML_SUCCESS)==retcode

You'd rather put the brakets in the macro (as the usual advice goes):
#define EXCEPTION_PARSER(T) do{if(!(T))throw InnateException();}while
(0)

IMHO you don't get the warning in the case of:
!retcode==TIXML_SUCCESS
because for some reason, it interprets TIXML_SUCCESS as 0 (false) and !
retcode is a valid boolean while
!TIXML_SUCCESS==retcode
is equivalent to
true == retcode
which is more problematic.

--
Michael