27077 total geeks with 3528 solutions
Recent challengers:
 Welcome, you are an anonymous user! [register] [login] Get a yourname@osix.net email address 



User's box

Forgot password?
New account

[b][url=http ://www.barbo urjackets.ne t/]barbour jackets on sale[/url][/ b] [b]<a href="http:/ /www.barbour jackets.net/ ">barbour jackets outlet</a>[/ b] [b][url=h ttp://www.ba rbourjackets .net/]barbou r jackets uk[/url][/b] http://www.m anreplicawat ches.org
<br><strong> <a href="http:/ /www.barbour jackets.net/ ">barbour jackets on sale</a></st rong> <stron g><a href="http:/ /www.barbour jackets.net/ ">barbour jackets outlet</a></ strong> <str ong><a href="http:/ /www.barbour jackets.net/ ">barbour jackets uk</a></stro ng>
<strong><a href="http:/ /www.watches er.com/">buy watches</a>< /strong> <br > <a href="http:/ /disocrevisw atches606481 .webs.com">b uy watches</a>< br> <strong><a href="http:/ /www.watches er.com/">wat ches sale</a></st rong> <br> <a href="http:/ /disocrevisw atches606481 .
[b][url=http ://www.gotow eca.org/]che ap beats by dre[/url][/b ] [b][url=ht tp://www.got oweca.org/]b eat by dre outlet[/url] [/b] [b]<a href="http:/ /www.gotowec a.org/">beat by dre headphones</ a>[/b] http://www.m anreplicawat ches.org/ replica watches, repl
<strong><a href="http:/ /www.gotowec a.org/">chea p beats by dre</a></str ong> <strong ><a href="http:/ /www.gotowec a.org/">beat by dre outlet</a></ strong> <str ong><a href="http:/ /www.gotowec a.org/">beat by dre headphones</ a></strong> <br><br><br> <br><br><br> <b

Donate and help us fund new challenges
Due Date: Oct 31
October Goal: $40.00
Gross: $0.00
Net Balance: $0.00
Left to go: $40.00

News Feeds
The Register
Carders punch holes
through Staples
VMware gives up on
smartphone concept
Palo Alto Networks
boxes spray
firewall creds
across the net
FedEx helps deliver
messages DIRECT to
its Blighty
Quantum key
security steps
outside the box
UNIX greybeards
threaten Debian
fork over systemd
Who"s that sniffing
around BlackBerry?
Oh, is it YOU
again, Lenovo?
ESNet"s 100 Gbps
Atlantic link
almost ready to
Watch live! NASA
video streams
Orionid meteor
shower ? or go
outside and look
Vote for us: We"re
slinging cash at
Doctor Who To Teach
Kids To Code
Security Company
Tries To Hide Flaws
By Threatening
Infringement Suit
A Look At Orion"s
Launch Abort System
32 Cities Want To
Challenge Big
Telecom, Build
Their Own Gigabit
Rumor: Lenovo In
Talks To Buy
Which Android
Devices Sacrifice
Battery-Life For
China Staging a
Nationwide Attack
On iCloud and
Microsoft Accounts
GNU Emacs 24.4
Released Today
More Eye Candy
Coming To Windows
Help ESR Stamp Out
CVS and SVN In Our
Article viewer

Dynamic argument list

Written by:shab
Published by:Nightscript
Published on:2004-01-05 00:31:04
Search OSI about C.More articles by shab.
 viewed 17132 times send this article printer friendly

Digg this!
    Rate this article :
If your reletivly new to C/C++ you might not have noticed it, but im rather sure you have used it. Useful when your writing functions like for example printf.

This is not a very big subject really, it's give things we will look @ in this article. I will list them below, with an description below.

  • ...
  • va_list
  • va_start
  • va_arg
  • va_end

This is what you put in your function declaration, if you have seen printf it looks like this:
 int printf(const char *, ...);

The ... show where the dynamic arguments begins, it can never be first and it can never be static arguments after it, you will understand why later.

The control handle for the arguments, on most systems it's a void *, but some tend to still hold on to char * for some reason.

control handle is not correct acually, it is the memory address that the argument is in, I will explain this more in va_start, you make one like this(rather obvious).
va_list va; /* Replace va with your name */

This in a macro, so no prototype can be shown. But this is how you could use it for example:
 void a(char b, ...) {
 va_list va;

 va_start(va, b);

What va_start really does it that is takes the memory address of b(argument 2) and place it in va_list, hence it's a void *. That means the second argument should be the argument before the dynamic arguments begins.

Just like va_start this is a macro, this one is a simple one just now, I really want to show you a prototype, but im afraid that's rather impossible. But here is an code example.
void a(char b, ...) {
 char c;
 va_list va;

 va_start(va, b);
 c = va_arg(va, char); }

The first argument is just like va_start the memory address, the second is how much memory it should move, if you would place int there is would be four, it also "return"(hence it's a macro) that memory.

I havn't acually checked what this acually does, but it probably free the memory, you use it like this:
void a(char b, ...) {
 char c;
 va_list va;

 va_start(va, b);
 c = va_arg(va, char);
 va_end(va); }

One single argument, as simple as anything.

Here is little function that I made up for example, I just coded it out of thin air while writing this article so excuse any misbehaviour.
#include <stdarg.h> /* I don't think I said it but here is it declared. */
#include <stdio.h>

void print(char *one, ...) {
 va_list va;
 char *p;

 for(p = one; p; p = va_arg(va, char *))

 return; }

I hope that all works ok, otherwise it could be very embarassing.

Did you like this article? There are hundreds more.

2006-04-21 20:33:52
wtf?? Mindless illiterate ramblings?
2006-04-21 23:41:05
lol - it does look a bit like that doesnt it!
Anonymously add a comment: (or register here)
(registration is really fast and we send you no spam)
BB Code is enabled.
Captcha Number:

Blogs: (People who have posted blogs on this subject..)
Creating a Lexical Analyzer in C on Tue 9th Dec 11am
#include<stdio.h> #include<string.h> #include<conio.h> #include<ctype.h> /*************************************** ************************* Functions prototype. **************************************** *************************/ void Open_File(
Controling digital circuit through computer on Tue 9th Dec 10am
this code access the lpt port.here only 4 of the total 8 pins are used but can be modified for full 8 pins.it has a complete GUI with mouse & keyboard interactive control panel.works well in win98, but not in winxp. #include<stdio.h> #include<conio.
/* Computerised Electrical Equipment Control */ /* PC BASED DEVICE CONTROLLER * on Tue 9th Dec 10am
#include<stdio.h> #include<conio.h> #include<dos.h> void main() { void tone(void); int p=0x0378; char ex={"Created By Mrc"}; int j; char ex1={"For Further Details & Improvements"}; int k; char ex2={"Contact : E-mail : anbudan
Calendar Program on Tue 9th Dec 10am
This program prints Weekdays of specified date. It even prints calendar of a given year too. /*Ccalendar library*/ #include<stdio.h> #include<string.h> #include<conio.h> int getNumberOfDays(int month,int year) { switch(month) { case
Calculator: on Tue 9th Dec 10am
#include"graphics.h" #include"dos.h" #include"stdio.h" #include"math.h" union REGS i,o; char text={ "7","8","9","*","4","5","6","/","1","2", "3","+","0","00",".","-","M","M+", "M-","+/-","MR","MC","x^2","sr","OFF","A C","CE","="}; int s=0,k=0,pass
This is a simple code that changes system time and date. It is written using c/c++ but can be easily converted to java. #include "stdio.h" #include "process.h" #include "dos.h" int main(void) { struct date new_date; struct date old_date; s
A C programme which can print the file name it is kept in on Tue 9th Dec 9am
BOOTSECTOR EDITOR: on Tue 9th Dec 9am
Code : /*program to save the partion table of your hard disk for future use. it will save your partition table in a file partition.dat */ #include<stdio.h> #include<bios.h> #include<conio.h> #include<stdlib.h> #include<ctype.h> void main () {
BLINKING STAR : on Tue 9th Dec 9am
#include<conio.h> #include<graphics.h> #include<stdlib.h> #include<dos.h> void main() { int gdriver=DETECT,gmode; int i,x,y; initgraph(&gdriver,&gmode,"e: cgi"); while(!kbhit()) { x=random(640); y=random(480); setcolor
// To print semicolons using C programming without using semicolons any where i on Tue 9th Dec 9am
// To print semicolons using C programming without using semicolons any where in the C code in program. // #include<stdio.h> #include<conio.h> void main() { char a; a=59; if(printf("%c",a)){} getch();

Test Yourself: (why not try testing your skill on this subject? Clicking the link will start the test.)
BSD sockets API by skrye

This is a test of your knowledge of the BSD socket interface
C Programming by keoki

This test is aimed at a C programmer that is at an intermediate level.

Your Ad Here
Copyright Open Source Institute, 2006