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cannot convert parameter from 'double (double)' to 'double (__cdecl *)(double)' error

 
 
Sydex
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      02-17-2005
When I compile code I get error
C2664: 'Integration::qgaus' : cannot convert parameter 1 from 'double
(double)' to 'double (__cdecl *)(double)'
in this part :
double Integration::quad2d(double (*func)(double,double))
{

nfunc = func ;

return qgaus(f1,x1,x2);//error there

}

//double (*nfunc)(double,double);

//double qgaus(double (*f)(double),double min,double max) const;

Please help


 
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Sydex
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      02-17-2005
I forgot
// double Integration::f1(double x)


 
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SnaiL
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      02-17-2005
What is f1? Your question is correct, but code you have provide is too
bad to understand where is a problem.

 
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Victor Bazarov
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      02-17-2005
Sydex wrote:
> When I compile code I get error
> C2664: 'Integration::qgaus' : cannot convert parameter 1 from 'double
> (double)' to 'double (__cdecl *)(double)'
> in this part :
> double Integration::quad2d(double (*func)(double,double))
> {
>
> nfunc = func ;
>
> return qgaus(f1,x1,x2);//error there


If 'f1' is a non-static member function, you won't be able to convert
it to a "pointer to function". Pointers to non-static members are not
compatible with pointers to functions. You need to rethink your code.

>
> }
>
> //double (*nfunc)(double,double);
>
> //double qgaus(double (*f)(double),double min,double max) const;
>
> Please help



V
 
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Peter Koch Larsen
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      02-17-2005

"Sydex" <(E-Mail Removed)> skrev i en meddelelse
news:cv2h71$tv1$(E-Mail Removed)-tv.ru...
> When I compile code I get error
> C2664: 'Integration::qgaus' : cannot convert parameter 1 from 'double
> (double)' to 'double (__cdecl *)(double)'


The errormessage indicates that you should pass a pointer to a function, but
passed the function itself.

> in this part :
> double Integration::quad2d(double (*func)(double,double))
> {
>
> nfunc = func ;
>
> return qgaus(f1,x1,x2);//error there


Try
return qgaus(&f1,x1,x2);
instead.

As an alternative, you might pass the function by reference.

/Peter
>
> }
>
> //double (*nfunc)(double,double);
>
> //double qgaus(double (*f)(double),double min,double max) const;
>
> Please help
>
>



 
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Sydex
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      02-17-2005
file "integration.h"
#ifndef INTEGRATION_H_

#define INTEGRATION_H_

class Integration

{

private:

double (*nfunc)(double,double);

double xsav;

double f1(double);

double f2(double);

double x1,y1,x2,y2;

int accuracy;

public:

Integration();

Integration(int naccuracy,double xx1,double xx2,double yy1,double yy2);

virtual ~Integration() { }

double qgaus(double (*f)(double),double min,double max) const;

double quad2d(double (*func)(double,double));

void SetIntLim(const double xx1,const double xx2,const double yy1,const
double yy2);

void SetAccuracy(const int naccuracy);

};

#endif

file "integration.cpp"

#include "stdafx.h"

#include "Integration.h"

Integration::Integration()

{

x1 = 0;

x2 = 1;

y1 = 0;

y2 = 1;

accuracy = 20;

}

Integration::Integration(int naccuracy,double xx1,double xx2,double
yy1,double yy2)

{

x1 = xx1 ;

x2 = xx2 ;

y1 = yy1;

y2 = yy2;

accuracy = naccuracy;

}

void Integration::SetAccuracy(const int naccuracy)

{

accuracy = naccuracy;

}

void Integration::SetIntLim(const double xx1,const double xx2,const double
yy1,const double yy2)

{

x1 = xx1 ;

x2 = xx2 ;

y1 = yy1;

y2 = yy2;

}

double Integration::qgaus(double (*f)(double),double min,double max) const

{

double sqrt3 = 1.7320508075688772935;

double step = (max - min)/accuracy;

double a,b = min;

double integral = 0;

if ((max - min) <= 0)

{

return 0 ;

}

for (int i=0;i<accuracy;i++)

{

a = b;

b +=step;

integral += ( (b-a)/2) * ( (*f)(-(b-a)/(2*sqrt3)+ (a+b)/2 ) + (*f)(
(b-a)/(sqrt3*2) + (a+b)/2 ));

}

return integral;

}

double Integration::quad2d(double (*func)(double,double))

{

nfunc = func ;

return qgaus(f1,x1,x2);

}

double Integration::f1(double x)

{

xsav = x ;

return qgaus(f2,y1,y2);

}

double Integration::f2(double y)

{

return nfunc(xsav,y);

}



"SnaiL" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> What is f1? Your question is correct, but code you have provide is too
> bad to understand where is a problem.
>



 
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Ron Natalie
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      02-17-2005
Sydex wrote:
> I forgot
> // double Integration::f1(double x)
>
>

Is this a non-static member?
 
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Ron Natalie
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      02-17-2005
Sydex wrote:

> double f1(double);


>
> double qgaus(double (*f)(double),double min,double max) const;
>
> return qgaus(f1,x1,x2);
>

f1 is a non-static member. You can not convert non-static member
functions to pointers to regular functions. It would appear
that your f1 function doesn't depend at all on the Integration
instances. Just declare it static:

static double f1(double);
 
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Matthias
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      02-17-2005
Victor Bazarov wrote:

> If 'f1' is a non-static member function, you won't be able to convert
> it to a "pointer to function". Pointers to non-static members are not
> compatible with pointers to functions. You need to rethink your code.


Why? Can't he just use an adaptor? Like std::mem_fun_ref or such?

--
Regards,
Matthias
 
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Victor Bazarov
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      02-17-2005
Matthias wrote:
> Victor Bazarov wrote:
>
>> If 'f1' is a non-static member function, you won't be able to convert
>> it to a "pointer to function". Pointers to non-static members are not
>> compatible with pointers to functions. You need to rethink your code.

>
>
> Why? Can't he just use an adaptor? Like std::mem_fun_ref or such?


They are functors. If the target for this adaptation is not a template,
it won't be able to pick it up. Consider

int foo(int (*f)()) // not a template
{
return f();
}

template<class F> int bar(F f) // a template
{
return f();
}

int fubar() // function
{
return 42;
}

struct barf // functor (like adaptors)
{
int operator()() { return 666; }
};

int main()
{
foo(fubar); // fine
bar(fubar); // fine
barf b;
foo(b); // error
bar(b); // fine
}

See the recent thread about passing a functor to 'qsort' in c.l.c++.m

Victor
 
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