overloading operator()

[Mohammad]

I'm implementing a c++ template class CScan to minipulate a series of
numbers.
I have implemented operator() to select a range of numbers it works
fine for an expression like:
scan1 = scan2(0, 99);

However, I have problem when I try something like:

scan1(0, 99) = scan2(100, 199);

In this case, a temporary object is created and destoryed without
copying the values to scan1. How can I accomplish this? Following is
some of the relavent code.


template<class T>
class CScan
{
public:
CScan() : m_nSize(0), m_pData(NULL)
{
}

CScan(ULONG nSize) : m_nSize(nSize)
{
m_pData = new T[m_nSize];
ZeroMemory(m_pD ata, m_nSize * sizeof(T));
}

CScan(T* pData, ULONG nSize) : m_nSize(nSize)
{
m_pData = new T[m_nSize];
CopyMemory(m_pD ata, pData, m_nSize * sizeof(T));
}

CScan(CScan& scan) : m_nSize(scan.m_ nSize)
{
m_pData = new T[m_nSize];
CopyMemory(m_pD ata, scan.m_pData, m_nSize * sizeof(T));
}

~CScan()
{
delete [] m_pData;
}

CScan& operator=(CScan & scan)
{
if (&scan == this)
{
return *this;
}
m_nSize = scan.m_nSize;
delete [] m_pData;
m_pData = new T[m_nSize];
CopyMemory(m_pD ata, scan.m_pData, m_nSize * sizeof(T));
return *this;
}

ULONG Size()
{
return m_nSize;
}

T& operator[](const ULONG nIndex)
{
if (nIndex >= m_nSize)
{
throw CScanError::Out sideBounds(m_nS ize, nIndex);
}
return m_pData[nIndex];
}

const T& operator[](const ULONG nIndex) const
{
if (nIndex >= m_nSize)
{
throw CScanError::Out sideBounds(m_nS ize, nIndex);
}
return m_pData[nIndex];
}

CScan operator()(cons t ULONG nFrom, const ULONG nTo) const
{
if (nFrom >= m_nSize)
{
throw CScanError::Out sideBounds(m_nS ize, nFrom);
}
if (nTo >= m_nSize)
{
throw CScanError::Out sideBounds(m_nS ize, nTo);
}
ULONG nSize = nTo - nFrom + 1;

if (nSize > 0)
{
return CScan(&m_pData[nFrom], nSize);
}
else
{
return CScan;
}
}

private:
T* m_pData;
ULONG m_nSize;
};

[Ron Natalie]

Re: overloading operator()

Mohammad wrote:[color=blue]
> I'm implementing a c++ template class CScan to minipulate a series of
> numbers.
> I have implemented operator() to select a range of numbers it works
> fine for an expression like:
> scan1 = scan2(0, 99);
>
> However, I have problem when I try something like:
>
> scan1(0, 99) = scan2(100, 199);
>
> In this case, a temporary object is created and destoryed without
> copying the values to scan1. How can I accomplish this? Following is
> some of the relavent code.
>[/color]

The trick is obviously not to use a temporary copy. The trick would to
have Scan::operator( ) not return a Scan directly, but an helper class that
would have a pointer/reference to the object that operator() was invoked
on and forward the copy/assignemnts to it (possibly remapping the indices).

[Mohammad]

Re: overloading operator()

"Ron Natalie" <ron@sensor.com > wrote in message news:<3f5e213a$ 0$46550$9a6e19e a@news.newshost ing.com>...[color=blue]
> Mohammad wrote:[color=green]
> > I'm implementing a c++ template class CScan to minipulate a series of
> > numbers.
> > I have implemented operator() to select a range of numbers it works
> > fine for an expression like:
> > scan1 = scan2(0, 99);
> >
> > However, I have problem when I try something like:
> >
> > scan1(0, 99) = scan2(100, 199);
> >
> > In this case, a temporary object is created and destoryed without
> > copying the values to scan1. How can I accomplish this? Following is
> > some of the relavent code.
> >[/color]
>
> The trick is obviously not to use a temporary copy. The trick would to
> have Scan::operator( ) not return a Scan directly, but an helper class that
> would have a pointer/reference to the object that operator() was invoked
> on and forward the copy/assignemnts to it (possibly remapping the indices).[/color]

I tried this approach but having compiling problems. It seems that
VC++ 6.0 does not support return value overloading. Are there any
other ways? It is at all possible to do something like that in C++.

[Ron Natalie]

Re: overloading operator()


"Mohammad" <mjamil314@hotm ail.com> wrote in message news:3d4a6581.0 309100632.79aa7 b63@posting.goo gle.com...[color=blue]
> "Ron Natalie" <ron@sensor.com > wrote in message news:<3f5e213a$ 0$46550$9a6e19e a@news.newshost ing.com>...[/color]
[color=blue]
> I tried this approach but having compiling problems. It seems that
> VC++ 6.0 does not support return value overloading. Are there any
> other ways? It is at all possible to do something like that in C++.[/color]

I dont' know that means. There's no such thing as return value overloading,
nor is one necessary to do what I suggested.

[Mohammad]

Re: overloading operator()

"Ron Natalie" <ron@sensor.com > wrote in message news:<3f5f42d3$ 0$51790$9a6e19e a@news.newshost ing.com>...[color=blue]
> "Mohammad" <mjamil314@hotm ail.com> wrote in message news:3d4a6581.0 309100632.79aa7 b63@posting.goo gle.com...[color=green]
> > "Ron Natalie" <ron@sensor.com > wrote in message news:<3f5e213a$ 0$46550$9a6e19e a@news.newshost ing.com>...[/color]
>[color=green]
> > I tried this approach but having compiling problems. It seems that
> > VC++ 6.0 does not support return value overloading. Are there any
> > other ways? It is at all possible to do something like that in C++.[/color]
>
> I dont' know that means. There's no such thing as return value overloading,
> nor is one necessary to do what I suggested.[/color]

Sincere thaks for your help! My confusion was partly due to some
problem with VC++ 6.0. My code compiled and work perfectly when I used
VC++ 7.0. Here are the relavent changes.

//Nested class in CScan

template<typena me T>
class CCopyScan
{
friend CScan<T>;
public:
CCopyScan(T* pData, ULONG nSize) :
m_pData(pData), m_nSize(nSize)
{
}

CCopyScan() :
m_pData(NULL), m_nSize(0)
{
}

CCopyScan(CCopy Scan& copyscan) :
m_pData(copysca n.m_pData), m_nSize(copysca n.m_nSize)
{
}

~CCopyScan()
{
}

CCopyScan& operator=(CCopy Scan& copyscan)
{
m_nSize = copyscan.m_nSiz e;
CopyMemory(m_pD ata, copyscan.m_pDat a, m_nSize * sizeof(T));
return *this;
}

private:
T* m_pData;
ULONG m_nSize;
};


//Overload assignment
CScan& operator=(const CCopyScan<T>& copyscan)
{
delete [] m_pData;
m_nSize = copyscan.m_nSiz e;
m_pData = new T[m_nSize];
CopyMemory(m_pD ata, copyscan.m_pDat a, m_nSize * sizeof(T));
return *this;
}

//New operator()
CCopyScan<T> operator()(cons t unsigned long nFrom, const unsigned
long nTo)
{
if (nFrom >= m_nSize)
{
throw;
}
if (nTo >= m_nSize)
{
throw;
}
unsigned long nSize = nTo - nFrom + 1L;
if (nSize > 0)
{
return CCopyScan<T>(&m _pData[nFrom], nSize);
}
else
{
return CCopyScan<T>();
}
}