overloading subscript

[murali]

hello everybody...

how can i overload the subscript operator with more than one
dimension... like [][][]....

if possible please give an example...

thank you...

[a]

Re: overloading subscript

Replacing the operators with the explicit function call will make this
clearer:

a[ x][ y ][ z ]
is the same thing as
a.operator[]( x ).operator[]( y ).operator[]( z ).

So the return types of the first 2 subscript operators must be types that
support a subscript operator.

A

[Jerry Coffin]

Re: overloading subscript

In article <1157866759.637 466.246860@b28g 2000cwb.googleg roups.com>,
murali.salem@gm ail.com says...

hello everybody...
>
how can i overload the subscript operator with more than one
dimension... like [][][]....

You can't do it directly -- you can either 1) overload some other
operator (most often ()), or 2) you can overload operator[] to return
some type that itself overloads operator[], and so on until you get to
the point of returning the individual item requested.

In the latter category, you have two general possibilities: use
something like std::vector<std ::vector<std::v ector<double >, or
create multi-dimension matrix class that overloads operator[] to return
a proxy, which overloads operator[] to return a proxy, [to a depth of
dimensions-1], with the final one actually returning the requested item.

// warnings:
// only minimally tested
// no attempt at const correctness
// no attempt at bounds checking
// only supports cube-shaped 3D matrices
//
template<class T, unsigned size>
class matrix3 {

T data[size][size][size];

friend class proxy;
friend class proxy2;

class proxy {
matrix3 &m_;
unsigned index1_, index2_;
public:
proxy(matrix3 &m, unsigned i1, unsigned i2)
: m_(m), index1_(i1), index2_(i2)
{}

T &operator[](unsigned index3) {
return m_.data[index1_][index2_][index3];
}
};

class proxy2 {
matrix3 &m_;
int index_;
public:
proxy2(matrix3 &m, unsigned d) : m_(m), index_(d) { }

proxy operator[](unsigned index2) {
return proxy(m_, index_, index2);
}
};
public:
proxy2 operator[](unsigned index) {
return proxy2(*this, index);
}
};

Used something like:



This code is intended only to demonstrate the basic concept involved --
as theh warnings hint, it's not suitable for serious use as it stands.

#include <iostream>
#include <iomanip>

int main() {

const int size = 4;

matrix3<double, sizem;

for (int x=0; x<size; x++) // initialize the contents
for (int y = 0; y<size; y++)
for (int z = 0; z<size; z++)
m[x][y][z] = x*100 + y * 10 + z;

for (int a=0; a<size; a++) // print out a diagonal
std::cout << std::setw(3)
<< std::setprecisi on(3)
<< std::setfill('0 ')
<< m[a][a][a] << "\n";
return 0;
}

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Marcus Kwok]

Re: overloading subscript

murali <murali.salem@g mail.comwrote:

how can i overload the subscript operator with more than one
dimension... like [][][]....
>
if possible please give an example...

See

http://www.parashift.com/c++-faq-lite/operator-overloading.html#faq-13.10

plus the two FAQs following it.

--
Marcus Kwok
Replace 'invalid' with 'net' to reply