Programming Forums > Application Development > C

colin mac · Dec 10th, 2007, 2:37 PM

Isn't an empty parenthesis only the same as void in C++, whereas in C it implies that the function can take a number of arguments?

grumpy · Dec 11th, 2007, 2:40 AM

Quote:

Originally Posted by xavier

Ok, the method signatures are generated with rpcgen. So i'm not modifying them.
Now , it's all interesting and stuff , and I do appreciate you taking the time to answer Grumpy.

But the question is quite simple . How can I work with " char ** " method signatures ?

And that simple question is insufficient because you have given no information about what the functions with "char ** method signatures" are required to do. Stating that they are generated by rpcgen gives no useful information whatsoever.

I do happen to know that rpcgen is a pre-compiler for a sun-proprietary rpc (remote procedure call) interface specification. To answer your question, I would have to see some information about your interface specification, learn the rpc language and learn about workings of the (proprietary) rpgen compiler. Pay me the going rate -- which applies to clients who expect the impossible from nothing -- of US$1000 (with a minimal non-refundable deposit in advance equivalent to 40 hours) and I'll think about it.....maybe.

You might have more luck by following simple advice: RTFM to learn about rpc and rpcgen for yourself.

xavier · Dec 11th, 2007, 4:32 AM

Ok mate, don't get all angry there. I thought that a signature like
char ** methodname () , is not such an uncommon thing in c, and that a simple and precise answer exists.

Don't feel like you HAVE to answer . It's a forum, if you want to answer then do it , otherwise don't .

Ps : To me , the question seemed easy enough . Given a method signature like :
char ** method(){} how do I return and use a " char * " variable.

grumpy · Dec 11th, 2007, 7:14 AM

And you have just demonstrated the art of asking a simple question that is completely meaningless.

Your question is like "how do I work with a stick?". There are many answers, depending on what you want to do with it. You can hit someone with it (a thought that tempts me mightily at the moment). You can throw it. You can carve it into a statue. You can burn it. You can dig a hole with it. You can use it to stir soup.

There is not a single answer to your question, unless you specify what the caller expects to do with the result returned by your function. You have not provided any such information, so there are many ways to "work with a method with a char ** return type".

xavier · Dec 11th, 2007, 2:13 PM

Ok, the answer .. doesn't even matter anymore but if I can make grumpy undestand what I'm asking I'll have learned at least one thing

.

So. From a function like : char ** ReturnString(){} I want to return a string. Then print the string on the screen.

Let's say that I only have this function and main. That's all. Can I be anymore clear ?

Narue · Dec 11th, 2007, 4:36 PM

>Can I be anymore clear ?
Clear as mud. Why would you want to do such a thing? The "why" usually results in a clearer requirement and that quickly brings you to the "how". As it is, I could do anything to meet your requirement, such as:

 c Syntax (Toggle Plain Text) 
#include <stdio.h>
 
char **foo ( void )
{
  static char *bar[] = { "a string" };
 
  return &bar[0];
}
 
int main ( void )
{
  puts ( *foo() );
 
  return 0;
}
#include <stdio.h>

char **foo ( void )
{
  static char *bar[] = { "a string" };

  return &bar[0];
}

int main ( void )
{
  puts ( *foo() );

  return 0;
}

xavier · Dec 12th, 2007, 11:54 PM

Ok, thanks for the answer.

grumpy · Dec 14th, 2007, 6:44 PM

Narue's answer is one of many valid possibilities, but you still need to realise that it depends on how you call it. For example, a simple change of main() to;

(Toggle Plain Text)

int main(void)
{
    puts( *(foo() + 2));
    return 0;
}

will yield undefined behaviour (implicitly assuming the static array has more elements than it does). Which comes back to why I was asking what you expect the function to do.

jim mcnamara · Dec 18th, 2007, 12:00 PM

Quote:

Originally Posted by colin mac

Isn't an empty parenthesis only the same as void in C++, whereas in C it implies that the function can take a number of arguments?

In C: int foo(); as a function declaration
does mean there is no parameter specification, which then means you can call foo with different numbers of arguments of differing datatypes and not have the compiler complain. You'll see examples of this in the C99 standard especially with regard to function pointers. The standards are merely showing what is allowed. It's not necessarily a good thing to do.

mbd · Dec 18th, 2007, 1:40 PM

Quote:

Originally Posted by Narue

>

 c Syntax (Toggle Plain Text) 
return &bar[0];
return &bar[0];

why not just

c Syntax (Toggle Plain Text)

return bar;

Dec 10th, 2007, 2:37 PM	#11
colin mac Newbie Join Date: Nov 2007 Location: Ireland Posts: 21 Rep Power: 0	Re: Function returning double pointer ? Isn't an empty parenthesis only the same as void in C++, whereas in C it implies that the function can take a number of arguments?

Dec 11th, 2007, 4:32 AM	#13
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 406 Rep Power: 5	Re: Function returning double pointer ? Ok mate, don't get all angry there. I thought that a signature like char methodname () , is not such an uncommon thing in c, and that a simple and precise answer exists. Don't feel like you HAVE to answer . It's a forum, if you want to answer then do it , otherwise don't . Ps : To me , the question seemed easy enough . Given a method signature like : char method(){} how do I return and use a " char * " variable. __________________ Don't take life too seriously, it's not permanent !

Dec 11th, 2007, 7:14 AM	#14
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Re: Function returning double pointer ? And you have just demonstrated the art of asking a simple question that is completely meaningless. Your question is like "how do I work with a stick?". There are many answers, depending on what you want to do with it. You can hit someone with it (a thought that tempts me mightily at the moment). You can throw it. You can carve it into a statue. You can burn it. You can dig a hole with it. You can use it to stir soup. There is not a single answer to your question, unless you specify what the caller expects to do with the result returned by your function. You have not provided any such information, so there are many ways to "work with a method with a char ** return type".

Dec 11th, 2007, 2:13 PM	#15
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 406 Rep Power: 5	Re: Function returning double pointer ? Ok, the answer .. doesn't even matter anymore but if I can make grumpy undestand what I'm asking I'll have learned at least one thing . So. From a function like : char ** ReturnString(){} I want to return a string. Then print the string on the screen. Let's say that I only have this function and main. That's all. Can I be anymore clear ? __________________ Don't take life too seriously, it's not permanent !

Dec 11th, 2007, 4:36 PM	#16
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	Re: Function returning double pointer ? >Can I be anymore clear ? Clear as mud. Why would you want to do such a thing? The "why" usually results in a clearer requirement and that quickly brings you to the "how". As it is, I could do anything to meet your requirement, such as: c Syntax (Toggle Plain Text) #include <stdio.h> char *foo ( void ) { static char bar[] = { "a string" }; return &bar[0]; } int main ( void ) { puts ( foo() ); return 0; } #include <stdio.h> char foo ( void ) { static char bar[] = { "a string" }; return &bar[0]; } int main ( void ) { puts ( *foo() ); return 0; } __________________ Even if the voices aren't real, they have some pretty good ideas.

Dec 12th, 2007, 11:54 PM	#17
xavier Professional Programmer Join Date: Oct 2004 Location: .ro Posts: 406 Rep Power: 5	Re: Function returning double pointer ? Ok, thanks for the answer. __________________ Don't take life too seriously, it's not permanent !

Dec 14th, 2007, 6:44 PM	#18
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Re: Function returning double pointer ? Narue's answer is one of many valid possibilities, but you still need to realise that it depends on how you call it. For example, a simple change of main() to; (Toggle Plain Text) int main(void) { puts( (foo() + 2)); return 0; } int main(void) { puts( (foo() + 2)); return 0; } will yield undefined behaviour (implicitly assuming the static array has more elements than it does). Which comes back to why I was asking what you expect the function to do.

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Programming Forums > Application Development > C

Function returning double pointer ?