function definition

[Tinkertim]

Re: function definition

On Oct 1, 3:02 pm, Keith Thompson <ks...@mib.orgw rote:

A format *string* is just one of many possible ways to specify the
arguments. Here's a rather contrived example:

Thanks, Keith! :) I've learned something new today. With a splash of
sanity, that is entirely convenient for corner cases.

Cheers,
--Tim

[Nick Keighley]

Re: function definition

On 1 Oct, 07:53, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:

On 1 Oct, 07:22, Tinkertim <tinker...@gmai l.comwrote:

On Oct 1, 1:01 pm, Keith Thompson <ks...@mib.orgw rote:

The point is that a printf-style format string isn't the only way to
determine the number and type of arguments [in a varargs function]
that are supposed to be
passed (though I think it's the only method used by any of the
functions in the standard library).

>
yes

<pedantic>
there's scanf() formats too
</pedantic>

--
Nick Keighley

[James Kuyper]

Re: function definition

Tinkertim wrote:

On Oct 1, 1:01 pm, Keith Thompson <ks...@mib.orgw rote:

....

>For example, I've seen variadic
>functions that take a series of char* arguments, with the end of the
>list marked by a (char*)NULL argument.

>
In that example, the function assumes all arguments to be char * type,
yes? You know your done when you hit a null argument. I'm not sure how
you could mix types without passing some kind of definition of the
incoming format.
>
I wasn't saying that a format was needed in all cases, just in cases
where arguments are of mixed types .. or is that what you were saying
that you've seen done? Sorry if I'm a little dense today :)

There's many other ways to handle mixed argument types. For instance,
in the IMSL C library, variable arguments are passed in groups. Each
group starts with an enumeration constant that identifies the type of
the group. Since the enumeration constant always has a type of 'int',
the function knows how to parse it. Then, knowing the group type, the
library function knows the precise type of each of the remaining members
of the argument group. A code value of 0 marks the end of the argument list.

The only general statement that you can make is that, knowing the values
of each of the first n arguments, the variadic function must have enough
information to determine whether there is another argument, and if so,
what type it has.

[Joachim Schmitz]

Re: function definition

Keith Thompson wrote:

Tinkertim <tinkertim@gmai l.comwrites:

>On Sep 30, 11:19 pm, Nick Keighley <nick_keighley_ nos...@hotmail. com>
>wrote:

>>>In very lay terms, "..." means arguments that complement format.
>>>
>>if I understood this I'm sure I'd disagree. Ellipsis (...) means
>>the number and type of arguments is not specified. It allows you
>>to pass a variable number of arguments with number specified
>>(somehow), possibly by the fixed arguments.

>>
>That's what I meant by complement, sorry. The number and type of
>arguments in the case above is determined by the format passed, where
>in your example its determined by a simple integer. %s %d determines
>two arguments of varying types, where as n = 5 determines five
>arguments of type int.
>>
>Complement is probably a bad choice of wording, however it appeared
>that the OP is not a native speaker so I tried to speak generally.

>
The point is that a printf-style format string isn't the only way to
determine the number and type of arguments that are supposed to be
passed (though I think it's the only method used by any of the
functions in the standard library). For example, I've seen variadic
functions that take a series of char* arguments, with the end of the
list marked by a (char*)NULL argument.

Another example is POSIX's open() which has an optional 3rd argument (mode_t
mode), which is only needed (and looked at) depending on the value of the
2nd arg (int oflag, needs to have O_CREAT set).

Bye, Jojo

[Keith Thompson]

Re: function definition

Nick Keighley <nick_keighley_ nospam@hotmail. comwrites:

On 1 Oct, 07:53, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:

>On 1 Oct, 07:22, Tinkertim <tinker...@gmai l.comwrote:

On Oct 1, 1:01 pm, Keith Thompson <ks...@mib.orgw rote:

>

The point is that a printf-style format string isn't the only way to
determine the number and type of arguments [in a varargs function]
that are supposed to be
passed (though I think it's the only method used by any of the
functions in the standard library).

>>
>yes

>
<pedantic>
there's scanf() formats too
</pedantic>

Well, yes, but I assert that scanf's format strings are in the *style*
of printf's format strings.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
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