Solved

Pure C - function with optional arguments only

Posted on 2003-11-03
6
516 Views
Last Modified: 2010-04-15
Hi,

I want to declare a function, which has no required parameters, but may have optional, and do it in pure C.

It's simple for functions having at least one parameter:
   void my_func( char *sFirst, ... );
and then accessing the optional using arg_list.

I want to define something like
   void my_func( ... );
but it's not valid :(


I'll appreciate your help.
0
Comment
Question by:migoEX
6 Comments
 
LVL 45

Expert Comment

by:sunnycoder
ID: 9669764
man 3 getopt

something like
while ((ch = getopt(argc, argv, "a:dhf:l:m:np:rs:v")) != EOF)
should serve your purpose

the above line of code is from syslogd source code
0
 
LVL 6

Assisted Solution

by:Ajar
Ajar earned 30 total points
ID: 9669871
hey you can always declare a pointer to a function without no args e.g


void ( * function)();

void  a_function_implementation(int  param1);
{
   // The param may not have been passed so the question is how
  // do you intend to find out wether a param has been passed or not;
  puts("INSIDE THE FUNCITON ");
}

int main(int argc,char* argv[])
{
    function = a_function_implementation;
    function();
}
0
 
LVL 5

Author Comment

by:migoEX
ID: 9670048
There is 1 problem left:

I want this function to be exported, and used by "external" functions. If in my H file I declare the function without parameters, the caller won't be able to compile a code, which is passing parameter. And vise versa - if I define it with parameter, a call without passing parameters won't compile.

PS: I'm not sure it's possible :)  but may be I'm missing some solution
0
U.S. Department of Agriculture and Acronis Access

With the new era of mobile computing, smartphones and tablets, wireless communications and cloud services, the USDA sought to take advantage of a mobilized workforce and the blurring lines between personal and corporate computing resources.

 
LVL 45

Expert Comment

by:sunnycoder
ID: 9670120
Even I would be interested in the solution if this was possible ...
0
 
LVL 5

Accepted Solution

by:
mtmike earned 170 total points
ID: 9670425
You can declare the function with an empty argument list, eg

void myfunc();

In C (not C++) this functions takes any number of arguments. The above means "arguments are still unspecified". You can specify the arguments later on when defining the function.

The above is also the reason that functions without arguments should be defined as

void myfunc(void);
0
 
LVL 5

Author Comment

by:migoEX
ID: 9670508
Thanks, mtmike!

That's exactly what I was looking for :)
0

Featured Post

Optimizing Cloud Backup for Low Bandwidth

With cloud storage prices going down a growing number of SMBs start to use it for backup storage. Unfortunately, business data volume rarely fits the average Internet speed. This article provides an overview of main Internet speed challenges and reveals backup best practices.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Preface I don't like visual development tools that are supposed to write a program for me. Even if it is Xcode and I can use Interface Builder. Yes, it is a perfect tool and has helped me a lot, mainly, in the beginning, when my programs were small…
This tutorial is posted by Aaron Wojnowski, administrator at SDKExpert.net.  To view more iPhone tutorials, visit www.sdkexpert.net. This is a very simple tutorial on finding the user's current location easily. In this tutorial, you will learn ho…
The goal of this video is to provide viewers with basic examples to understand and use structures in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to use strings and some functions related to them in the C programming language.

932 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

8 Experts available now in Live!

Get 1:1 Help Now