how to overload subscript of 2D-array

[DaVinci]

/* how to overload the operation [] ,subscipt of 2D-array?
* how can I get element through piece[j],rather than piece(i)[j]?
* */
#include"global.h"
using namespace std;
class Piece
{
public:
Piece()
{
for(size_t i = 0;i<2;i++)
for(size_t j = 0;j<3;j++)
{
piece[j] = i+ j;
}
for(size_t i=0;i<2;i++)
{
std::copy(piece,piece+3,ostream_iterator<int>(cout," "));
cout<<endl;
}
cout<<"----------------------"<<endl;
}
int* operator()(const int& t)//change operator() to operator[] is
wrong ,why?
{
i = t; //
return piece;
}
int operator[](const int & t)
{
return this->operator()(i)[t];
}
private:
int i;//witchout varible i,how can I implement overload the () , []
or[],[]
int piece[2][3];
};
//----------------------------------------
int main()
{
Piece p ;
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
{
cout<<p(i)[j]<<" ";//p[j],??
}
cout<<endl;
}
}
/*
//output is
0 1 2
1 2 3

 

[Jonathan Mcdougall]

/* how to overload the operation [] ,subscipt of 2D-array?
* how can I get element through piece[j],rather than piece(i)[j]?
* */

This is a FAQ, http://www.parashift.com/c++-faq-lite/.


Jonathan

 

[Axter]

/* how to overload the operation [] ,subscipt of 2D-array?
* how can I get element through piece[j],rather than piece(i)[j]?
* */
#include"global.h"
using namespace std;
class Piece
{
public:
Piece()
{
for(size_t i = 0;i<2;i++)
for(size_t j = 0;j<3;j++)
{
piece[j] = i+ j;
}
for(size_t i=0;i<2;i++)
{
std::copy(piece,piece+3,ostream_iterator<int>(cout," "));
cout<<endl;
}
cout<<"----------------------"<<endl;
}
int* operator()(const int& t)//change operator() to operator[] is
wrong ,why?
{
i = t; //
return piece;
}
int operator[](const int & t)
{
return this->operator()(i)[t];
}
private:
int i;//witchout varible i,how can I implement overload the () , []
or[],[]
int piece[2][3];
};
//----------------------------------------
int main()
{
Piece p ;
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
{
cout<<p(i)[j]<<" ";//p[j],??
}
cout<<endl;
}
}
/*
//output is
0 1 2
1 2 3

I recommend against using the method posted in the C++ FAQ.
It recommends you use a non-standard syntax.

If you want to use standard syntax check out the following link for an
example:
http://code.axter.com/dynamic_2d_array.h

However, for most requirements, I recommend using a vector of vector.
Example:
int col = 123;
int row = 456;
vector<vector<int> > My2dArray(col, vector<int>(row));


You can reference both the above vector code and the dynamic_2d_array
class using double index ([][])
My2dArray[0][0] = 99;

Check out the following link for wrapper classes using vector of
vector:
http://www.codeguru.com/forum/showthread.php?t=231046
http://www.codeguru.com/forum/showthread.php?s=&threadid=297838

 

[DaVinci]

/* how to overload the operation [] ,subscipt of 2D-array?
* how can I get element through piece[j],rather than piece(i)[j]?
* */
#include"global.h"
using namespace std;
class Piece
{
public:
Piece()
{
for(size_t i = 0;i<2;i++)
for(size_t j = 0;j<3;j++)
{
piece[j] = i+ j;
}
for(size_t i=0;i<2;i++)
{
std::copy(piece,piece+3,ostream_iterator<int>(cout," "));
cout<<endl;
}
cout<<"----------------------"<<endl;
}
int* operator()(const int& t)//change operator() to operator[] is
wrong ,why?
{
i = t; //
return piece;
}
int operator[](const int & t)
{
return this->operator()(i)[t];
}
private:
int i;//witchout varible i,how can I implement overload the () , []
or[],[]
int piece[2][3];
};
//----------------------------------------
int main()
{
Piece p ;
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
{
cout<<p(i)[j]<<" ";//p[j],??
}
cout<<endl;
}
}
/*
//output is
0 1 2
1 2 3

I recommend against using the method posted in the C++ FAQ.
It recommends you use a non-standard syntax.

If you want to use standard syntax check out the following link for an
example:
http://code.axter.com/dynamic_2d_array.h

However, for most requirements, I recommend using a vector of vector.
Example:
int col = 123;
int row = 456;
vector<vector<int> > My2dArray(col, vector<int>(row));


You can reference both the above vector code and the dynamic_2d_array
class using double index ([][])
My2dArray[0][0] = 99;

Check out the following link for wrapper classes using vector of
vector:
http://www.codeguru.com/forum/showthread.php?t=231046
http://www.codeguru.com/forum/showthread.php?s=&threadid=297838

yes,I know vector<vector<int> > but here

The class Piece 's purpose 's isnot just for 2D-array,it was desiged to
support some other
operation such as void draw_grahic(),
void move_left() and so on.
But I must first Encapsulate the 2d-array int piece[2][3] as private
data.
and supply operator[][] to get it's data,
is there way to overload the operator[] twice to meet my need?

 

[Jonathan Mcdougall]

The class Piece 's purpose 's isnot just for 2D-array,it was desiged to
support some other
operation such as void draw_grahic(),
void move_left() and so on.
But I must first Encapsulate the 2d-array int piece[2][3] as private
data.
and supply operator[][] to get it's data,
is there way to overload the operator[] twice to meet my need?

If that's what you really want, just make an operator[] that returns a
proxy. Then, put another operator[] in that proxy that gives a value:

# include <vector>
# include <cstddef>

class test;

class proxy
{
friend class test;

public:
int operator[](std::size_t index)
{
return v_[index];
}

private:
proxy(std::vector<int>& v)
: v_(v)
{
}

std::vector<int>& v_;
};


class test
{
public:
proxy operator[](std::size_t index)
{
return proxy(v_[index]);
}

private:
std::vector< std::vector<int> > v_;
};

int main()
{
test t;
int i = t[1][2];
}

This is completly artificial, since std::vector already has a subscript
operator, but you should get the picture.


Jonathan

 

[Axter]

/* how to overload the operation [] ,subscipt of 2D-array?
* how can I get element through piece[j],rather than piece(i)[j]?
* */
#include"global.h"
using namespace std;
class Piece
{
public:
Piece()
{
for(size_t i = 0;i<2;i++)
for(size_t j = 0;j<3;j++)
{
piece[j] = i+ j;
}
for(size_t i=0;i<2;i++)
{
std::copy(piece,piece+3,ostream_iterator<int>(cout," "));
cout<<endl;
}
cout<<"----------------------"<<endl;
}
int* operator()(const int& t)//change operator() to operator[] is
wrong ,why?
{
i = t; //
return piece;
}
int operator[](const int & t)
{
return this->operator()(i)[t];
}
private:
int i;//witchout varible i,how can I implement overload the () , []
or[],[]
int piece[2][3];
};
//----------------------------------------
int main()
{
Piece p ;
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
{
cout<<p(i)[j]<<" ";//p[j],??
}
cout<<endl;
}
}
/*
//output is
0 1 2
1 2 3

I recommend against using the method posted in the C++ FAQ.
It recommends you use a non-standard syntax.

If you want to use standard syntax check out the following link for an
example:
http://code.axter.com/dynamic_2d_array.h

However, for most requirements, I recommend using a vector of vector.
Example:
int col = 123;
int row = 456;
vector<vector<int> > My2dArray(col, vector<int>(row));


You can reference both the above vector code and the dynamic_2d_array
class using double index ([][])
My2dArray[0][0] = 99;

Check out the following link for wrapper classes using vector of
vector:
http://www.codeguru.com/forum/showthread.php?t=231046
http://www.codeguru.com/forum/showthread.php?s=&threadid=297838

yes,I know vector<vector<int> > but here

The class Piece 's purpose 's isnot just for 2D-array,it was desiged to
support some other
operation such as void draw_grahic(),
void move_left() and so on.
But I must first Encapsulate the 2d-array int piece[2][3] as private
data.
and supply operator[][] to get it's data,
is there way to overload the operator[] twice to meet my need?

Yes.
Did you look at the first link I posted?
http://code.axter.com/dynamic_2d_array.h

The above link doesn't use vector vector, and it's able to use
operator[] to return a 2D array without using a proxy class.