pls explain this macro

[Ravi]

#define JOIN(s1,s2) printf("%s = %s %s = %s",#s1,s1,#s2, s2)

[Ian Collins]

Ravi wrote:

#define JOIN(s1,s2) printf("%s = %s %s = %s",#s1,s1,#s2, s2)

What's "pls"? Please put your question in your message body.

Have you tried the macro? Your C book should explain the operation of #
on a macro argument.

--
Ian Collins.

[santosh]

On Wednesday 18 Jul 2007 1:53 pm, in comp.lang.c, Ravi
<ra*********@gm ail.comwrote:
Message ID: <11************ **********@j4g2 000prf.googlegr oups.com>

#define JOIN(s1,s2) printf("%s = %s %s = %s",#s1,s1,#s2, s2)

The name JOIN is rather misleading. The # preprocessor operator
causes it's accompanying argument to be "stringised ", i.e., for it
to enclosed within double quotes before further processing.

So in your case, if you write:

JOIN(str1, str2)

the replacement token would be:

printf("%s = %s %s = %s", "str1", str1, "str2", str2);

[Richard Heathfield]

santosh said:

On Wednesday 18 Jul 2007 1:53 pm, in comp.lang.c, Ravi
<ra*********@gm ail.comwrote:
Message ID: <11************ **********@j4g2 000prf.googlegr oups.com>

>#define JOIN(s1,s2) printf("%s = %s %s = %s",#s1,s1,#s2, s2)

The name JOIN is rather misleading. The # preprocessor operator
causes it's accompanying argument to be "stringised ", i.e., for it
to enclosed within double quotes before further processing.

So in your case, if you write:

JOIN(str1, str2)

the replacement token would be:

printf("%s = %s %s = %s", "str1", str1, "str2", str2);

Not quite. It would be:

printf("%s = %s %s = %s","str1",str1 ,"str2",str2 )

The most important difference is, of course, that your semicolon is
spurious.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[santosh]

On Wednesday 18 Jul 2007 3:12 pm, in comp.lang.c, Richard Heathfield
<rj*@see.sig.in validwrote:
Message ID: <6f************ *********@bt.co m>

santosh said:

>On Wednesday 18 Jul 2007 1:53 pm, in comp.lang.c, Ravi
<ra*********@g mail.comwrote:
Message ID: <11************ **********@j4g2 000prf.googlegr oups.com>

>>#define JOIN(s1,s2) printf("%s = %s %s = %s",#s1,s1,#s2, s2)

[ ... ]

>So in your case, if you write:

JOIN(str1, str2)

the replacement token would be:

printf("%s = %s %s = %s", "str1", str1, "str2", str2);

Not quite. It would be:

printf("%s = %s %s = %s","str1",str1 ,"str2",str2 )

Yes!

The most important difference is, of course, that your semicolon is
spurious.

Indeed. I'd meant to write:

JOIN(str1, str2);