How to use # & ## operator in C??

[gu ming]

Hi Guys,
Do you know how to use # & ## operator in C?

For example, what's meaning for following code?

#define macro(a) #a

[Richard Heathfield]

gu ming said:

Hi Guys,
Do you know how to use # & ## operator in C?

For example, what's meaning for following code?

#define macro(a) #a

"The C Programming Language", 2nd edition, by Kernighan and Ritchie, page
90, from about half-way down the page, right down to the bottom.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[Peter Nilsson]

Richard Heathfield wrote:

gu ming said:

Do you know how to use # & ## operator in C?
For example, what's meaning for following code?
#define macro(a) #a

"The C Programming Language", 2nd edition, by Kernighan and Ritchie, page
90, from about half-way down the page, right down to the bottom.

I'm surprised Steve Summit's online course notes don't get quite as
much airplay
as his FAQ...

http://c-faq.com/~scs/cclass/
http://c-faq.com/~scs/cclass/int/sx6a.html

--
Peter

[spibou]

Peter Nilsson wrote:

Richard Heathfield wrote:

gu ming said:

Do you know how to use # & ## operator in C?
For example, what's meaning for following code?
#define macro(a) #a

"The C Programming Language", 2nd edition, by Kernighan and Ritchie, page
90, from about half-way down the page, right down to the bottom.

I'm surprised Steve Summit's online course notes don't get quite as
much airplay
as his FAQ...

http://c-faq.com/~scs/cclass/
http://c-faq.com/~scs/cclass/int/sx6a.html

The link http://c-faq.com/~scs/cclass/int/sx6a.html does not mention
the # and ## operators. Otherwise the course is excellent.

[BubbaGump]

On 23 Jul 2006 20:26:09 -0700, "gu ming" <gu******@gmail.comwrote:

>Hi Guys,
Do you know how to use # & ## operator in C?

For example, what's meaning for following code?

#define macro(a) #a

# can be used for turning an identifier into a string and ## can be
used to create an identifier from a macro's arguments, although I find
## hurts more than it helps. Once a set of code get's large enough,
## starts to make it harder to understand because the names of the
generated variables and functions can no longer be searched for as
easily. They're hidden behind macros.
#include <stdio.h>
#define PRINT_INT(x) \
do { printf("value of %s: %d\n", #x, x); } while(0)

#define CALL_FUNC(x) do { Func##x(); } while(0)
void FuncRead()
{
printf("Entered FuncRead\n");
}
void FuncWrite()
{
printf("Entered FuncWrite\n");
}
int main()
{
int my_variable = 57;

PRINT_INT(my_variable);
CALL_FUNC(Read);
CALL_FUNC(Write);

return 0;
}