defining a macro

[junky_fellow]

Hi,

Are there any issues if I define a macro as follows:

#define MY_MACRO(a,b); my_function((a),(b));

and calling this macro as follows,
MY_MACRO(a,b);


Is it a good idea to include ";" as a part of macro ? Can this have
any undesired effect ?


thanks in advance for any help ....

 

[Lew Pitcher]

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Hash: SHA1

Hi,

Are there any issues if I define a macro as follows:

#define MY_MACRO(a,b); my_function((a),(b));

and calling this macro as follows,
MY_MACRO(a,b);


Is it a good idea to include ";" as a part of macro ? Can this have
any undesired effect ?

Consider the effect of macro expansion on a code fragment like

if (a)
MY_MACRO(a,b);
else
MY_MACRO(c,d);

What will your extraneous semicolon do to this construct?

HTH
- --
Lew Pitcher

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[Bart]

Hi,

Are there any issues if I define a macro as follows:

#define MY_MACRO(a,b); my_function((a),(b));

and calling this macro as follows,
MY_MACRO(a,b);


Is it a good idea to include ";" as a part of macro ? Can this have
any undesired effect ?

Besides being very misleading I don't know. Have you tried:

if(something)
MY_MACRO(a, b);

Regards,
Bart.

 

[Michael Mair]

Are there any issues if I define a macro as follows:

#define MY_MACRO(a,b); my_function((a),(b));

This is wrongly grouped:
#define MY_MACRO(a,b) ;my_function((a),(b));
is equivalent.

and calling this macro as follows,
MY_MACRO(a,b);

Is it a good idea to include ";" as a part of macro ? Can this have
any undesired effect ?

if (foo)
MY_MACRO(a,b);
will compile, link, and seemingly "ignore foo".

See also
http://c-faq.com/cpp/multistmt.html


Cheers
Michael

 

[junky_fellow]

This is wrongly grouped:
#define MY_MACRO(a,b) ;my_function((a),(b));
is equivalent.


if (foo)
MY_MACRO(a,b);
will compile, link, and seemingly "ignore foo".

I tried that and it seemed to work fine. Please note that ";" is a
part of macro
and during preprocessing MY_MACRO(a,b); will be replaced by
my_function(a,b);
So, there should not be any problem.

Am I missing something ?

 

[Tak-Shing Chan]

I tried that and it seemed to work fine. Please note that ";" is a
part of macro
and during preprocessing MY_MACRO(a,b); will be replaced by
my_function(a,b);
So, there should not be any problem.

Am I missing something ?

Yes. The code above expands into:

if (foo)
;my_function((a),(b));;

Which is semantically equivalent to:

if (foo)
; /* do nothing, effectively ignoring foo */
my_function((a), (b));
; /* do nothing again */

Tak-Shing

 

[Richard Tobin]

[/QUOTE]

I tried that and it seemed to work fine. Please note that ";" is a
part of macro and during preprocessing MY_MACRO(a,b); will be replaced by
my_function(a,b);

It doesn't work like that. You can't put stuff after the close
bracket and expect corresponding stuff in the program to be replaced.

-- Richard

 

[Snis Pilbor]

Hi,

Are there any issues if I define a macro as follows:

#define MY_MACRO(a,b); my_function((a),(b));

and calling this macro as follows,
MY_MACRO(a,b);


Is it a good idea to include ";" as a part of macro ? Can this have
any undesired effect ?


thanks in advance for any help ....

What I like to do is this:

#define MY_MACRO(a,b) do \
{ \
my_function((a),(b)); \
} \
while( 0 )

This way, MY_MACRO inherits the same semantics as if it were a
function: if you "call" it without manually adding a semicolon, the
compiler will report an error because the ending while of a do-loop
must be terminated with a semicolon. And, more importantly, it works
fine regardless of how you combine it with if's, else's, etc.

This is an FAQ btw =) You should set a goal of reading through the
comp.lang.c FAQs, not all in one sitting but a bit at a time. Once you
finish, you will gain 2,345,098,721 experience points

Snis P.

 

[junky_fellow]

Yes. The code above expands into:

if (foo)
;my_function((a),(b));;

Which is semantically equivalent to:

if (foo)
; /* do nothing, effectively ignoring foo */
my_function((a), (b));
; /* do nothing again */

Now I got this. Thanks everyone ...