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How to make below code works:
My questions is: Is it possible to make a global static functions pointer point to a member function which a object?Code:int (*pf)(void);
class myclass
{
myclass() {}
~myclass() {}
public:
int myf(void) { return 1; }
};
...
myclass mc;
pf = &mc.mf; // ?? How to make it works?
...
No. Only member pointers can point to members.
BTW - don't use (void) in C++ to indicate "no parameters". It looks as if you don't know what you're doing.Code:int (myclass::*pf)();
I just found VC7.1 generated the default construct in this style (e.g. "CClass(void)").Quote:
Originally Posted by Graham
non-static member functions are not like non-member functions.Code:int (*pf)(void);
class myclass
{
myclass() {}
~myclass() {}
public:
static int myf(void) { return 1; }
};
...
pf = &myclass::mf;
...
They have an additional implicit this parameter, and may have a different calling convention than non-member functions or static member functions.
If you want to implement a delegate, then, you can use boost::function or wrap an object of type myclass (or a pointer to such object) bound to a member function pointer, in a structure.
Usually, callback mechanism are better handled with more generic mechanism.Code:struct MyClassDelegate {
int (myclass::*method)();
myclass& object;
int operator()() {return object.*method();}
};
For example, a reference to an abstract base class may be used by a function... In that case, derive from this abstract base class, and write something similar to MyClassDelegate.
C style functions may use a function pointer and a void* context parameter.
In that case, pass a myclass* as context parameter and defined a function:
Code:Type function(..., void* context) {
return static_cast<myclass*>(context)->myf(...);
}
IMHO, it's not a problem. It's only a stylistical issue.Quote:
Originally Posted by shaohao
The (void) syntax has been named abomination, because it's really ugly and not necessary in pure C++ code.
I prefer to avoid this syntax, but I admit that other programmers use it.
I think it is should be removed from the language completely, if that is somehow possible. Perhaps in C++0x.Quote:
Originally Posted by SuperKoko
I just don't like it at all, and using empty paranthesis to indicate no arguments makes much more sense to me.
And on Graham's comment, I would have to agree. No offense to the OP, because he didn't know any better,
but I would definitely brand a fellow co-worker an "idiot" if he used such notation in his code.
Moreover, on a side note, I got a question wrong on a Java exam the other day because of this abomination.
The question was this...
Which of the following are acceptable method declarations?
1) void method1()
2) void method2(void)
3) ...
4) ...
5) ...
I don't remember what the rest were. Now, I knew #1 was obviously an answer. But since I have only been using java for a semester or two, I wasn't sure about #2. Since C++ and Java are extremely similar in syntax, I figured "Well, it is horrid to use it in C++, but the compiler won't complain. So it would technically be an acceptable method declaration. So I will just have to assume the same for Java."
Nope, big mistake. Can't do that in Java. Only empty paranthesis.
I know it was my mistake for assuming, but it was a mistake that should never have been made because it is stupid to have in C++ to begin with.
Good grief, I wouldn't go so far as to call it an abomination, but my point was simply that, whilst it serves a purpose in C, it is strictly redundant in C++ - it serves absolutely no purpose. Putting it in makes it look as if you don't know the difference between C (empty parentheses means "no parameter information given") and C++ (empty parentheses means "no parameters"). No disrespect to the OP, who's possibly still learning, but people make (employment) decisions on clues like that.
i think it looks alot better with a void in it. its more explicit and quick for me.Quote:
Originally Posted by SuperKoko
user-preferenced i geuss.
pre-judging or w/e its called in english.Quote:
Originally Posted by Graham
like im now pre-judging that because you say that you dont care about that evry person is diffrent and likes it in his own way.
bad stylish wise? how can style be bad? i understand some basic styling like tabbing scopes/namespaces/classes for easy reading but some other person might not like this and do it his way
Note that I didn't said it was an abomination. I was only refering to the history of (void) when Doug McIlroy and Dennis Ritchie said that it was an abomination to Bjarne Stroustup, he first removed it from the language... But, later, the C interoperability problems it produced were too serious... And (void) was brought back into the language.Quote:
Originally Posted by Graham
dcjr84:
IMHO, it would not be a good idea to remove it from C++0x, because it would have no benefit and would break much existing code and complicate interoperability with C: new headers would use more macros such as:
It would make headers harder to read, not easier.Code:#ifdef __cplusplus
#define NO_ARG ()
#else
#define NO_ARG (void)
#endif
I don't think that this special syntax has introduced bugs in non-aware programmers or that they've lost much time because of it.
dcjr84, language constructs are not removed from a language only because they're ugly useless or you don't like them... Otherwise, having a standard would be useless... Letting compiler vendors judging what they like and what they don't would work as well...
Backward compatibility and C interoperability are really very very important.
Such a huge modification (it is not a small modification such as removal of trigraphs, it's a modification which would affect probably more than ten percent of the existing C++ code base) would cost several billion dollars, perhaps more.
Benefits would be invisible.
Hence, you notice I used the words "if that is somehow possible." If it would disrupt the entire backwards compatibility with existing C programs, then I suppose you have no choice but to leave it be.Quote:
Originally Posted by SuperKoko
You can say what you want , but I have a very strong opinion about this and I am not going to change it regardless of what arguments you make for it. The use of void in place of empty paranthesis in a C++ program to indicate no arguments is an abomination. I just think it is stupid, pointless, and makes you look like you don't know how to program in C++. I would brand any fellow programmer incompetent if he used such notation in his code. Period.
Furthermore, if I was in a management position at a company where I had to hire people, I can guarantee you I would not hire someone based on this alone, regardless of how well they did in other areas.
Why do you have such a strong opinion about this? What makes this an absolute abomination?Quote:
Originally Posted by dcjr84
That's tough! I could very well see someone who has to maintain C and C++ code on a daily basis decide that he will always specify void because (a) it is easier to have a habit that works across multiple languages and (b) because you are more likely to make mistakes if you try to do things one way in one language and one way in another -- especially when the languages are inter-operable. If someone proved themselves to be a very capable programmer and gave me the above argument about why he uses 'void' in C++, I wouldn't call him incompetent.Quote:
Originally Posted by dcjr84
Out of curiosity, do you say programmers are incompetent if they use post-increment operators where pre-increment operators will do?
Wow!!! :eek:Quote:
Originally Posted by dcjr84
It is just my opinion. I think it's attrocious, and that's all there is to it.Quote:
Why do you have such a strong opinion about this? What makes this an absolute abomination?
I might, it depends on the situation. But at least the post-increment operator or pre-increment operator have a meaning behind their use. It is not pointless to use either one of them. you could not just omit one of them entirely from a situation and still get them same result. Using void to indicate no parameters in C++ is a huge waste of time and code space, which leads me to my next point...Quote:
Out of curiosity, do you say programmers are incompetent if they use post-increment operators where pre-increment operators will do?
I will even take this one step further. Let's say somehow a programmer did get hired into my company that did this without me knowing. After a while, I would notice he used such notation. I would keep track, over the weekly/bi-weekly pay period, of how many times he used the word void in a no argument function signature. Then, I would figure out on average how long it takes him to type void each time. I would multiply the two together to find out how much total time he has wasted typing void in such situations, multiply it by his hourly rate, and deduct it from his paycheck.Quote:
Quote:
Originally Posted by dcjr84
Furthermore, if I was in a management position at a company where I had to hire people, I can guarantee you I would not hire someone based on this alone, regardless of how well they did in other areas.
Wow!!!
I am sure others feel the same way, but about other aspects of the language. Like people using void main() instead of int main(), etc, etc. It's just the way I feel about it.
I would not hire a programmer if when I asked him about pointer to functions and pointers to member functions and he started discussing abomination of void and programming incompetencies related to it.. ;) :D