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

[Sydex]

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

[Sydex]

I forgot
// double Integration::f1(double x)

[SnaiL]

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

[Peter Koch Larsen]

"Sydex" <sy****@comtv.ru> skrev i en meddelelse
news:cv**********@news.comcor-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

[Victor Bazarov]

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

[Ron Natalie]

Sydex wrote:

I forgot
// double Integration::f1(double x)

Is this a non-static member?

[Sydex]

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" <VL********@MIRATECH.BIZ> wrote in message
news:11**********************@g14g2000cwa.googlegr oups.com...

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

[Ron Natalie]

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);

[Matthias]

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

[Victor Bazarov]

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

[Andrey Tarasevich]

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?

An adaptor would convert member function pointer to functional object.
The OP needs to convert member function pointer to regular function
pointer. The latter is cannot be done by standard means in C++. There
are platform-specific implementations that can do that, but this is a
completely different story.

--
Best regards,
Andrey Tarasevich

[Matthias]

Andrey Tarasevich wrote:

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?

An adaptor would convert member function pointer to functional object.
The OP needs to convert member function pointer to regular function
pointer. The latter is cannot be done by standard means in C++. There
are platform-specific implementations that can do that, but this is a
completely different story.

Hm, this qgaus function is his own function right? Why not just change
the first parameter to take a function object instead of a ptr to
function? ^^

Am I missing something?
--
Regards,
Matthias

[Victor Bazarov]

Matthias wrote:

[...]
Hm, this qgaus function is his own function right? Why not just change
the first parameter to take a function object instead of a ptr to
function? ^^

Am I missing something?

I think so. If you change it to an object (or a reference), then it
will be unable to accept function pointers. Unless it is converted
into a template, there is no accepting both function pointers and
functors. See my other reply if you haven't already.

V