Re: Funciton with function pointer argument

From:
Vladyslav Lazarenko <vlazarenko@volanttrading.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 1 Apr 2009 05:41:15 -0700 (PDT)
Message-ID:
<5fdf65ef-d6de-4b14-9f07-3640e369c58d@r33g2000yqn.googlegroups.com>
On Apr 1, 1:05 am, oalfishcivil <yuefei...@gmail.com> wrote:

On Mar 31, 3:16 pm, Andrey Bulat <andrey.bu...@gmail.com> wrote:

On Mar 31, 8:50 pm, Andrey Tarasevich <andreytarasev...@hotmail.com>
wrote:

Vladyslav Lazarenko wrote:

On Mar 31, 12:42 pm, oalfishcivil <yuefei...@gmail.com> wrote:

I have a function double solver(double (*pf)(double), double to=

l)

However, it would be nice if solver could work for function
double func(double x,double para) since the codes are similar.
How could I do that? Thanks


1) Create the base function: "double solver(double x, double para)"
2) Move implementation from "double solver(double (*pf)(double),
double tol)" except invocation of the function pointed by "pf" to t=

hat

function.
3) Change "double solver(double (*pf)(double), double tol)" functio=

n

to call "double solver(double x, double para)" with x = result of
invocation of the function pointed by "pf".


Usually, a callback-based interface implies that the callback functio=

n

needs to be called repeatedly from the 'solver' function, each time w=

ith

different arguments and different results. In general case there's no
way to replace all these invocations with a single invocation in
advance. If that were possible, there probably wouldn't be a callback
there in the first place.

--
Best regards,
Andrey Tarasevich


I can propose for discussion following simple sample:

class Functor2
{
public:
        Functor2(int A, int B): a(A),b(B){}
        int a;
        int b;
        virtual int operator()()
    {
                return b;
    }

};

class Functor1: public Functor2
{
public:
        Functor1(int A): Functor2(A, 0){}
        virtual int operator()()
    {
        return a;
    }

};

int solver(Functor2* p, int d)
{
        return (*p)() + d;

}

int main()
{
    Functor1 f1(5);
    Functor2 f2(3,2);
    int ret;
    ret = solver(&f1, 7);
    ret = solver(&f2, 7);

}

As for me it is more valuable construction versus global variable (and
much more readeble).
(It works on VS2008)

Best wishes
Andrey Bulat


Really appreciate your example and others' suggestions. I am writing a
code use bisection method to find roots in given bounds for
functions like double func(double x) or double func(double x,double
para). Since I have several different such functions, I want to write
a bisection method function which can take this functions as argument
instead of adding the bisection method in each function which will
produce a lot more repetitive codes. I think your method here would
work for me although it's not that elegant(not your fault). Thanks
Yuefei


Just a friendly suggestion - use templates instead of polymorphism.

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