optional arguments..

[Jason]

Hi there,

I'm new to C .. have a very basic question .. hope someone has the
patience to help!

I want to declare a function that has optional parameters and I want to
initialize the non supplied parameters .. how do I do this?

eg:

// this obviously isn't allowed .. but need to acheive something
similar
int function foo (int a=0, int b=0, int c=0, int d=0) {

// do something
return 0;
}

// I want to be able to call this function with any or all the
parameters

foo (2, 5,); // in this case a=2, b=5, c should be 0 and d should be 0


How do I accomplish this?


Thanks a bunch guys!

[Peter Nilsson]

Re: optional arguments..

Jason wrote:[color=blue]
> Hi there,
>
> I'm new to C .. have a very basic question .. hope someone has the
> patience to help!
>
> I want to declare a function that has optional parameters and I want to
> initialize the non supplied parameters .. how do I do this?[/color]

You can't in C. You can mimic it to some extent (e.g. va_xxxx macros in
<stdarg.h>), but it isn't pretty or recommended, especially for
beginners.
[color=blue]
> eg:
>
> // this obviously isn't allowed .. but need to acheive something
> similar
> int function foo (int a=0, int b=0, int c=0, int d=0) {
>
> // do something
> return 0;
> }[/color]

If you really want to do this, try C++.

If you need to use C only, then you should elaborate on what your
problem actually is, rather than state what you think is the solution
to an as yet unspecified problem.

--
Peter

[Jason]

Re: optional arguments..

Thanks Peter. To be honest I haven't programmed in ages and was
wondering if this was possible in C at all.

Cheers!

[jacob navia]

Re: optional arguments..

Jason wrote:[color=blue]
> Hi there,
>
> I'm new to C .. have a very basic question .. hope someone has the
> patience to help!
>
> I want to declare a function that has optional parameters and I want to
> initialize the non supplied parameters .. how do I do this?
>
> eg:
>
> // this obviously isn't allowed .. but need to acheive something
> similar
> int function foo (int a=0, int b=0, int c=0, int d=0) {
>
> // do something
> return 0;
> }
>
> // I want to be able to call this function with any or all the
> parameters
>
> foo (2, 5,); // in this case a=2, b=5, c should be 0 and d should be 0
>
>
> How do I accomplish this?
>
>
> Thanks a bunch guys!
>[/color]
The lcc-win32 compiler implements this as an extension. The syntax is
the same as you wrote.

http://www.cs.virginia.edu/~lcc-win32

[Default User]

Re: optional arguments..

Jason wrote:
[color=blue]
> Thanks Peter. To be honest I haven't programmed in ages and was
> wondering if this was possible in C at all.[/color]


Please review the information below.



Brian
--
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header.

[Peter Shaggy Haywood]

Re: optional arguments..

Groovy hepcat Jason was jivin' on 27 Apr 2006 18:28:25 -0700 in
comp.lang.c.
optional arguments..'s a cool scene! Dig it!
[color=blue]
>I'm new to C .. have a very basic question .. hope someone has the
>patience to help![/color]

No worries! We're very patient with people who are on-topic and
willing to learn.
[color=blue]
>I want to declare a function that has optional parameters and I want to
>initialize the non supplied parameters .. how do I do this?[/color]

It wouldn't be too hard, using a variadic function. You'd need
another parameter, though, representing the number of variadic
arguments passed.
[color=blue]
>eg:
>
>// this obviously isn't allowed .. but need to acheive something
>similar
>int function foo (int a=0, int b=0, int c=0, int d=0) {
>
> // do something
> return 0;
>}[/color]

#include <stdarg.h>

int foo(size_t nargs, ...)
{
int a = 0, b = 0, c = 0, d = 0;
int *arr[4];
va_list ap;
size_t i;

arr[0] = &a;
arr[1] = &b;
arr[2] = &c;
arr[3] = &d;

va_start(ap, nargs);

for(i = 0; i < nargs; i++)
{
*arr[i] = va_arg(ap, int);
}

va_end(ap);

/* Do something. */

return 0;
}

--

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