conditional structure vs. function pointers

[Gary Wessle]

Hi

I have a group of functions which have the same signature.
void fun_n(void);
according to a conditional structure "be it if-else or switch-case" I
get to choose which one to run.

conditional structure verifies a short type and fires the fun_n in its
block.

is this a good candidate for a function pointer? I was googleing and
wanted to practice a bit but only if it is a better approach.

any guidance is appreciated.

thanks

[Dan Bloomquist]

Re: conditional structure vs. function pointers



Gary Wessle wrote:

Hi
>
I have a group of functions which have the same signature.
void fun_n(void);
according to a conditional structure "be it if-else or switch-case" I
get to choose which one to run.
>
conditional structure verifies a short type and fires the fun_n in its
block.
>
is this a good candidate for a function pointer? I was googleing and
wanted to practice a bit but only if it is a better approach.

I'm new here but...
If you aren't passing the function or keeping an array of functions or
need your calls to be mutable at run time, (or?), I can't see a good
reason for it.

I'd think keeping your code 'simple' would have priority.

Best, Dan.

[Victor Bazarov]

Re: conditional structure vs. function pointers

Gary Wessle wrote:

I have a group of functions which have the same signature.
void fun_n(void);
according to a conditional structure "be it if-else or switch-case" I
get to choose which one to run.
>
conditional structure verifies a short type and fires the fun_n in its
block.
>
is this a good candidate for a function pointer? I was googleing and
wanted to practice a bit but only if it is a better approach.

Depending on your condition[s] an array of pointers, or a 'std::map'
of value/ptr-to-func pairs might actually be clearer than a bunch of
'if/else' statements or a switch pile.

V
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[Gary Wessle]

Re: conditional structure vs. function pointers

"Victor Bazarov" <v.Abazarov@com Acast.netwrites :

Gary Wessle wrote:

I have a group of functions which have the same signature.
void fun_n(void);
according to a conditional structure "be it if-else or switch-case" I
get to choose which one to run.

conditional structure verifies a short type and fires the fun_n in its
block.

is this a good candidate for a function pointer? I was googleing and
wanted to practice a bit but only if it is a better approach.

>
Depending on your condition[s] an array of pointers, or a 'std::map'
of value/ptr-to-func pairs might actually be clearer than a bunch of
'if/else' statements or a switch pile.
>
V

good idea. help me with it please.


class Type2 {

public:
void mine();

};

void Type2::mine(){
cout << "mine pointer de-referenced" << endl;
}


class Type1 {
Type2 type2;
typedef void (*pf)();
std::vector<pfp tr_fun;
public:
void fire();

};

Type1::Type1( Type2 t2 ):
type2( t2 ),
names("mine his hers theirs etc"),
...
{}

void Type1::fire(){
/* build a vector<stringfr om "names" above */
for each item in this vector
build the string to look like &mine and vec.push_back(" &mine").

and fire it by *(vec[i]) i.e de-referenced element number i in the
vector.

but this is a string vector and not a <address of functionsvector .

how can I solve this in an elegant way.

thanks

[raxitsheth2000@yahoo.co.in]

Re: conditional structure vs. function pointers

Hmm, Cryptic Question

U didnt mentioned anything about class or OO relation etc.

class MyInterface
{
void fun_n(void);
};




class Implementation1 : (assume public or protected)MyInt erface
{

};

Implementation :: fun_n()
{
//Definition. of fun_n
}



same way Implementation2 ,3...n

now using MyInterface ptr, you can invoke fun_n of any implementation.

this is possilbly one solution (!) (But May Not fit in to your
requrenment, as you have not specified about class or OO dependancy)


--raxit sheth

[Victor Bazarov]

Re: conditional structure vs. function pointers

Gary Wessle wrote:

"Victor Bazarov" <v.Abazarov@com Acast.netwrites :
>

>Gary Wessle wrote:

>>I have a group of functions which have the same signature.
>>void fun_n(void);
>>according to a conditional structure "be it if-else or switch-case"
>>I get to choose which one to run.
>>>
>>conditional structure verifies a short type and fires the fun_n in
>>its block.
>>>
>>is this a good candidate for a function pointer? I was googleing and
>>wanted to practice a bit but only if it is a better approach.

>>
>Depending on your condition[s] an array of pointers, or a 'std::map'
>of value/ptr-to-func pairs might actually be clearer than a bunch of
>'if/else' statements or a switch pile.
>>
>V

>
good idea. help me with it please.
>
>
class Type2 {
>
public:
void mine();

This is a non-static member function.

>
};
>
void Type2::mine(){
cout << "mine pointer de-referenced" << endl;
}
>
>
class Type1 {
Type2 type2;
typedef void (*pf)();

This is a pointer to function. In you intended to assign &Type2::mine
to 'pf', you cannot. For that you need to declare 'pf' as a "pointer
to member of Type2":

typedef void (Type2::*pf)();

std::vector<pfp tr_fun;
public:
void fire();
>
};
>
Type1::Type1( Type2 t2 ):
type2( t2 ),
names("mine his hers theirs etc"),
...
{}
>
void Type1::fire(){
/* build a vector<stringfr om "names" above */
for each item in this vector
build the string to look like &mine and vec.push_back(" &mine").
>
and fire it by *(vec[i]) i.e de-referenced element number i in the
vector.
>
but this is a string vector and not a <address of functionsvector .
>
how can I solve this in an elegant way.

There is no "elegant" way of solving it. Somewhere you will _have_
to have a bunch of 'if' statements and compare your strings to some
known values and then push the pointers to members into your vector.

What I actually proposed to you was a 'std::map', like this:

class Type1 {
...
std::map<std::s tring, pfmymap;
...
};

You will need to fill it in (the c-tor is a good place if 'mymap'
is non-static). You should also consider having it as a static data
member, and initialise it only once.

Filling it in should be similar to

mymap["mine"] = &Type1::mine ;

and so on.

V
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