switch-case via function pointers...

[Rahul]

Hi,

I planning to replace the switch-case with an array of function
pointers, the index for the array would be the case integers. Each
case block would be implemented as a seperate function. It works fine
when all the functions have the exact signature like the return types
and formal input parameters.

In my case, some functions accept a different number of arguements.
Hence i can't have the array of different function pointers, is there
any alternative or work around to get it done by using the same
concept of invoking each case via function pointers?

Thanks in advance ! ! !

 

[Paavo Helde]

Hi,

I planning to replace the switch-case with an array of function
pointers, the index for the array would be the case integers. Each
case block would be implemented as a seperate function. It works fine
when all the functions have the exact signature like the return types
and formal input parameters.

In my case, some functions accept a different number of arguements.
Hence i can't have the array of different function pointers, is there
any alternative or work around to get it done by using the same
concept of invoking each case via function pointers?

Some options:

1. Create some wrapper functions so that all signatures are the same.

2. Put functions with different signatures into different arrays.

3. Define a union containing different types of function pointers and
make an array of unions. As in case 2, the call site must decide in
advance which signature to call.

hth
Paavo

 

[Jeff Schwab]

Hi,

I planning to replace the switch-case with an array of function
pointers, the index for the array would be the case integers. Each
case block would be implemented as a seperate function. It works fine
when all the functions have the exact signature like the return types
and formal input parameters.

In my case, some functions accept a different number of arguements.
Hence i can't have the array of different function pointers, is there
any alternative or work around to get it done by using the same
concept of invoking each case via function pointers?

Thanks in advance ! ! !

If the functions are all callable using similar syntax, you could use
the TR1 "function" template.

http://www.devx.com/cplus/10MinuteSolution/32455/0/page/1

If there are minor variations in syntax, you may need another level of
compile-time indirection, e.g. to provide default values for unused
parameters.

long add2(int a, int b) { return long(a) + b; }
long add3(int a, int b, int c =0) { return long(a) + b + c; }

#include <cassert>
#include <vector>

#include <tr1/functional>

int main() {
std::vector<std::tr1::function<long (int, int)> > funcs;

funcs.push_back(add2);
funcs.push_back(add3);

assert(funcs.at(0)(3, 4) == funcs.at(1)(3,4));
}

 

[Rahul]

Hi,

I planning to replace the switch-case with an array of function
pointers, the index for the array would be the case integers. Each
case block would be implemented as a seperate function. It works fine
when all the functions have the exact signature like the return types
and formal input parameters.

In my case, some functions accept a different number of arguements.
Hence i can't have the array of different function pointers, is there
any alternative or work around to get it done by using the same
concept of invoking each case via function pointers?

Thanks in advance ! ! !

Just found a way to implement this. I can use functionoid concept to
implement an array of function pointers to functions of different
parameters,

http://www.parashift.com/c++-faq-lite/pointers-to-members.html#faq-33.10

But yes, this can work only with c++ ;-) not with c :-(