Static member array of pointers to member functions

Question

I am trying to define in a .cpp file an attribute which should be an array of pointers to member functions of a class named Hand.
Both the array and the functions are members of Hand and the array is static(please correct me if it should not).
This is what I reached:

static bool Hand::*(Hand::hfunctions)[] ()=
{&Hand::has_sflush,&Hand::has_poker,&Hand::has_full,&Hand::has_flush,
&Hand::has_straight,&Hand::has_trio,&Hand::has_2pair,&Hand::has_pair};

I get this error: hand.cpp:96:42: error: declaration of ‘hfunctions’ as array of functions.
I guess the type definition is worng so I need to know how can I make the definition right

What's the question ?

hivert
– hivert

2013-07-23 21:41:50 +00:00
Commented Jul 23, 2013 at 21:41 — hivert
– hivert, Commented Jul 23, 2013 at 21:41
What is it you're actually trying to achieve here?

Timo Geusch
– Timo Geusch

2013-07-23 21:41:53 +00:00
Commented Jul 23, 2013 at 21:41 — Timo Geusch
– Timo Geusch, Commented Jul 23, 2013 at 21:41

anatolyg · Accepted Answer · 2013-07-23 22:30:44Z

3

The syntax is a rather convoluted one:

class Hand
{
    bool has_sflush();
    static bool (Hand::*hfunctions[])();
    ...
};

bool (Hand::*Hand::hfunctions[])() = {&Hand::has_sflush, ...};

A way to get to this is by gradually increasing complexity, using cdecl.org to check yourself at each step:

int (*hFunctions)()

declare hFunctions as pointer to function returning int

int (Hand::*hFunctions)()

declare hFunctions as pointer to member of class Hand function returning int

Warning: Unsupported in C -- 'pointer to member of class'

int (Hand::*hFunctions[])()

declare hFunctions as array of pointer to member of class Hand function returning int

Warning: Unsupported in C -- 'pointer to member of class'

Now replace int by bool (sadly, cdecl.org doesn't understand bool); so you get the syntax of the declaration.

For the definition, replace hFunctions by Hand::hFunctions, and add the initialization part, like you did.

edited Jul 23, 2013 at 22:30

answered Jul 23, 2013 at 22:17

anatolyg

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1 Comment

tuket Over a year ago

cdecl.org, I didn't know that tool, thanks!! If it worked for c++ would be even better

utnapistim · Accepted Answer · 2013-07-23 22:37:07Z

2

Both the array and the functions are members of Hand and the array is static(please correct me if it should not).

If I understand correctly what you are asking, you should not. You should abstract the operation as a base class, specialize it and hold the array as an array of pointers to the base class:

struct Match // need a better name
{
     virtual bool matches() = 0;
     virtual ~Match() = default;
};

struct MatchSFlush: public Match { ... };

class Hand
{
    static std::vector<std::unique_ptr<Match>> matches;
};

edited Jul 23, 2013 at 22:37

answered Jul 23, 2013 at 22:30

utnapistim

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4 Comments

anatolyg Over a year ago

"you should not" - i guess this means "you should not implement this the way you did"; the question was "should the array be static?". Anyway +1.

utnapistim Over a year ago

Yes, it was about not implementing it this way. Usually when you need to create an array of functions to abstract behavior, that means "go virtual".

tuket Over a year ago

I will have to research in order to understand this answer. Thanks for the effort.

utnapistim Over a year ago

My point was that your has_sflush, has_poker (and so on) functions should not be a set of member functions in Hand, but a hierarchy of classes outside of it.

a.lasram · Accepted Answer · 2013-07-23 22:09:29Z

1

If you have non static member functions with no arguments and returning bool you should write something like

typedef bool (Hand::*hfunction_non_static)();
hfunction_non_static f_non_static [] =
{
    &Hand::has_sflush,
    &Hand::has_poker,
    .......
}; 
Hand h;
(h.*f_non_static[0])();

If you have static functions you should write something like

typedef bool (*hfunction_static)();
hfunction_static f_static [] = {&Hand::has_sflush, ....};
f_static[0]();

answered Jul 23, 2013 at 22:09

a.lasram

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1 Comment

tuket Over a year ago

Thanks! This is not exactly what I was asking because I had trouble when I had to tell the compiler that "hfunctions is member of Hand" in the .cpp file. Anyway I have learned a lot from your answer, for instance that the usage of typedef makes this easier.

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