Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!cs.utexas.edu!uunet!microsoft!t-wader
From: t-wader@microsoft.UUCP (Wade Richards)
Newsgroups: comp.lang.c
Subject: Re: printf
Message-ID: <8174@microsoft.UUCP>
Date: 24 Oct 89 01:52:13 GMT
References: <543@uwm.edu>
Reply-To: t-wader@microsoft.UUCP (Wade Richards)
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Organization: Microsoft Corp., Redmond WA
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Disclaimer: I don't always agree with my boss, why should he agree with me?

In article <543@uwm.edu> zhao@csd4.csd.uwm.edu (T.C. Zhao) writes:
=}I recently came across a piece of c code:(both a and b are integers)
=}printf("%d"+(a),b);
=}in passes compiler without any problem, what does this code mean ?
=}
=}--
=}----------------------------------------------
=}Internet:       zhao@csd4.csd.uwm.edu
=}  BITNET:       zhao%csd4.csd.uwm.edu@WISCMAC3.BITNET

That code is the same as:

	switch( a ) {
	case 0: printf( "%d", b );	break;
	case 1: printf( "d", b );	break;
	case 2: printf( "", b );	break;
	default: printf( (char *)random(), b );	break;
	}

The expression "%d"+(a) evaluates to a pointer to the string "%d\0" somewhere
in memory, plus the integer a.  The sum of a "pointer to type X" and an integer
is another "pointer to type X", pointing to the a-th following object of type
X.  This is not at all clear.  By way of example, if the pointer pointed to
memory location 1000, and an object of type X took up 5 bytes, then the pointer
plus 2 would be: 1000 + 2*5 = 1010.

Hope this helps.

	--- Wade

BYW, the (char *)random() simply means a (lot likely valid) pointer to anywhere.