variable-length argument list ???

[null]

hi, i heard it's possible to do functions with variable-length argument list. is that true? if so, where can i find more info about it?

i mean, how are they prototyped etc

thanx

null

[Salem]

Very true....

#include <stdio.h>
#include <stdarg.h>

// sum a list of integers
// the list ends when a zero is detected
int sum_args ( int first, ... ) {
    va_list ap;
    int     val, sum = first;
    va_start(ap,first);
    while ( (val=va_arg(ap,int)) != 0 ) {
        sum += val;
    }
    va_end(ap);
    return sum;
}

int main() {
    printf( "%d\n", sum_args(1,2,3,4,5,6,0) );
    return 0;
}

[null]

hi Salem, thanks for the example. just a couple of questions on it...the:

while ( (val=va_arg(ap,int)) != 0 )

is it automaticaly incremented (to point to the next argument) ?

also all the:

va_...

are they global? which geader file are they in?

also, on a different subject, do you know of any good advanced c book? i can only find books with the usual stuff (vars, pointers, structs,functions,loops etc). i'm looking for something that picks where the usual books stop and goes from there. something with real-life problems and solutions, like good ways of programming certain things.

It seems that good books on c are occupying less space on bookstore shelves now...it's just full of vb, databases, java, web stuff etc...

thanks for the help

null

[Troll_King]

I'm not trying to answer for Salem or anything. I admit, he is one of the best programmers here. Anyway, since this is a public board, and I've used va_arg a couple of times although not so elegantly as Salems code, yes, it does search for the number of arguements by incrementing through them using pointers.

I heard that it is utilized practicaly by library functions such as printf that have a control string. Otherwise use a linked list.

Regarding books, try "C Unleashed". It is certainly and advanced C book. And no I have not read it all. I have looked through it. I know for a fact it's a great book.

Anyway there is a point that I would like to make. If you want to become a great C programmer than investigate C++. Doing this will improve your C skills because C++ in a small to medium way is the art of building smart functions using C.

[Salem]

> va_start(ap,first);
Uses the last named argument (first) to establish a pointer to the first unnamed argument, and stores that reference in ap.

> (val=va_arg(ap,int))
Returns the current argument (in this case of type int), and advances ap to the next argument.

> va_end(ap);
Generally tidies up any loose ends.

If you were using a printf type control string (%s, %d etc), then you would perhaps have some kind of if/case statement to call
(s_ptr=va_arg(ap,char*)) // %s
(d_val=va_arg(ap,int)) // %d
As appropriate

> are they global? which geader file are they in?
<fx: takes a wild stab in the dark>
#include <stdarg.h>
Wasn't it obvious this would be the answer?

As for books - hard to say
http://www.accu.org/bookreviews/publ...advanced_c.htm
might be helpful in perhaps choosing books to actually go and look at before making a decision.

[null]

lol...

yes, that was very obvious...sorry man...and thanks for replying


null