C syntax

ashlesha · 07-04-2006, 06:17 PM

i m very unsure of what this line means exactly:

typedef int (*initcall_t)(void);

why is there a void there?

i would think this typedef means that we can use another name for a pointer to an integer called initcall_t....what does the void do?
OR
is it a pointer to a function? why is there a typedef there in that case? is it typedef'ing' the integer that the function returns? what is the point of this?

i would very much appreciate a prompt reply!
Thank you!

Ashlesha.

theNbomr · 07-04-2006, 06:33 PM

Literally, the declaration is:

initcall_t is a pointer to a function taking no arguments (void arg list) and returning an int. 'typedef'ing it makes it look like it is a native data type.

--- rod.

tuxdev · 07-04-2006, 06:38 PM

It is a pointer-to-function typedef, so that you can easily make code that takes one of them without trying to deal with the tough and possibly confusing syntax. All you need to do is declare things with that type, which is a lot simpler than if you had to do it the hard way everywhere.

ashlesha · 07-04-2006, 06:41 PM

thank you very much...

i have another query

#define __setup(str, fn) \
static char __setup_str_##fn[] __initdata = str; \
static struct kernel_param __setup_##fn __attribute__((unused)) __initsetup = { __setup_str_##fn, fn }

#endif

what does this do?
i dont understand the use of ## in the definitions..

thankyou!
a

ashlesha · 07-04-2006, 06:43 PM

tuxdev-

i m trying to figure out the kernel code for a mips microprocessor....

m using debian linux on my pc..

ashlesha.

taylor_venable · 07-04-2006, 07:31 PM

## is used to textually concatenate two things together, usually one (or both) of them a parameter. Say you want to make one long string out of a parameter and a fixed value. In the macro definition, you can use "a_long_ ## param". If param is "foo" the result is "a_long_foo" or if param is "bar" you get "a_long_bar". See the CPP documentation for details.

tuxdev · 07-04-2006, 07:53 PM

It might help for us to know what file this comes out of, or the general purpose of this macro (beyond just setup). Setup what?