Re: How do I create a function in my library for passing user callback function
- From: ymuntyan@xxxxxxxxx
- Date: Mon, 14 Apr 2008 20:43:06 -0700 (PDT)
On Apr 14, 7:07 pm, Ben Bacarisse <ben.use...@xxxxxxxxx> wrote:
"Bill Reid" <hormelf...@xxxxxxxxxxxxxxxx> writes:
Ben Bacarisse <ben.use...@xxxxxxxxx> wrote in message
news:87bq4cci3r.fsf@xxxxxxxxxxxx
"Bill Reid" <hormelf...@xxxxxxxxxxxxxxxx> writes:
<snip lots>
<snip>
extern void my_library_function (int (*)(const char*));
library_c.c
#include "library_h.h"
void my_library_function(int my_callback_function(const char*)) {
}
You must be aware that is this not the normal syntax.
Sure it is. I use it all the time, so it's normal to me.
That's fine, but I would not suggest it as a "first example" or in
"how to" code just because it needs more explanation.
Usually, the
function definition is similar to the declaration, except the ';' is
replaced by the function body.
Right. Let me clue you in on something about me: I try to
conserve keystrokes where they AREN'T needed, and use
them where they help me understand my own code.
Again, that is up to you, but in my editor copying the prototype is
fewer keystrokes than writing the two forms you used.
<snip>
Function pointer parameters usually look like this:
void my_library_function(int (*my_callback_function)(const char*)) {}
Sure. But then I have to type "(*)" (three whole extra characters!)
where I don't need to type any more characters, because the two
ways of defining the parameters ARE TOTALLY FUNCTIONALLY
IDENTICAL.
which is, of course, how you wrote it in the function's prototype.
There, I'm forced to write it that way, unless I again want to
type unwanted characters...WHICH I DON'T.
This I don't get. You can save two keystrokes if you use the same
style in the prototype (but let me guess: a parameter name in a
prototype is "unwanted characters").
<snip>
The answer is that there is a special dispensation:
A declaration of a parameter as ''function returning type'' shall be
adjusted to ''pointer to function returning type''
Great, which of course completely conforms to the basic
idea above that a function name is actually a function pointer
by the simple necessity of computer science...I'm assuming
this is "standard" language, so despite you calling it a
"special dispensation" IT IS TOTALLY CONFORMING
"STANDARD" SYNTAX.
Yes, but that does not make it good syntax. With your example, a
beginner would wonder why a variable declared to store this callback
pointer looked so different to the parameter that receives it. C has
enough special cases already.
I don't want to have a style war about how you write your programs,
but in "how to" postings I would suggest being consistent and avoiding
special cases.
And the posters who declare "syntax error stupid", should
at least see if their compiler agrees.
At least some of the "fuzz" here may have come from
your use of two different styles.
My hypothesis is: Bill didn't write that stuff intentionally.
He meant to write a pointer or whatever, doesn't matter what.
But he happened to write *correct* code, and then was told
three times (two in great details about how dumb he is
making that mistake and not seeing and admitting it) he has
a syntax error there. What's the real cause of the "fuzz"
again?
A troll? Don't feed the troll, how about that! BS, in other
words.
Yevgen
.
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