Writing operator functions

V

valerij

Yes, hi

How to write "operator +" and "operator =" functions in a class with
a defined constructor? The following code demonstrates that I don't
really understand how to do it... I think it has something to do with
the compiler calling the destructor twice. Could someone point out
where I go wrong?
P.S.: The error it gives is "Debug Assertion Failure ....." (at run
time)
P.P.S: Everything else works just fine (without the use of "operator
+"
and "operator =" functions)

//code "tested" on Microsoft Visual C++ 6.0
#include <iostream>

using namespace std;

class DatArray {
public:
int rows, columns;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (DatArray da1); //problematic
void operator ++ ();
//DatArray operator + (double d1); //does not work
};

DatArray::DatArray(int r, int c) {
int c1;
rows = r;
columns = c;
a = new double* [rows];
for (c1 = 0; c1 < rows; c1++) a[c1] = new double [columns];
}

DatArray::~DatArray() {
int c1;
for (c1 = 0; c1 < rows; c1++) delete [] a[c1];
delete [] a;
}

void DatArray::eek:perator = (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = d1;
}

void DatArray::eek:perator = (DatArray da1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = da1.a[c1][c2];
}

void DatArray::eek:perator ++ () {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2]++;
}

/*DatArray DatArray::eek:perator + (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = a[c1][c2] + d1;
return *this;
}*/

int main() {
int c1, c2;
DatArray myarray(3, 4), myarray2(3, 4);
myarray = 10.1;
for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray.a[c1][c2]
<< " ";
cout << endl;
}
cout << endl;
for (c1 = 0; c1 < 100; c1++) myarray++;
//myarray2 = myarray + 100; //this should be simpler, but does not
work ?!?!?!?!?!
myarray2 = myarray;
for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray2.a[c1][c2]
<< " ";
cout << endl;
}
cin.get(); //currently, after this, ERROR ... WHY?!?!?!?!?! (how to
fix this?!?!?!?!?)
return 0;
}
//end of code "tested" on Microsoft Visual C++ 6.0

Thanks,
Valerij
 
P

Piyo

valerij said:
Yes, hi

How to write "operator +" and "operator =" functions in a class with
a defined constructor? The following code demonstrates that I don't
really understand how to do it... I think it has something to do with
the compiler calling the destructor twice. Could someone point out
where I go wrong?
P.S.: The error it gives is "Debug Assertion Failure ....." (at run
time)
P.P.S: Everything else works just fine (without the use of "operator
+"
and "operator =" functions)

//code "tested" on Microsoft Visual C++ 6.0
#include <iostream>

using namespace std;

class DatArray {
public:
int rows, columns;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (DatArray da1); //problematic
void operator ++ ();
//DatArray operator + (double d1); //does not work
};
Click to expand...

My gut instinct tells me you are missing a Copy Constructor.
I'd have to look at it closely to tell later :)
 
V

Victor Bazarov

valerij said:
Yes, hi

How to write "operator +" and "operator =" functions in a class with
a defined constructor? The following code demonstrates that I don't
really understand how to do it... I think it has something to do with
the compiler calling the destructor twice. Could someone point out
where I go wrong?
P.S.: The error it gives is "Debug Assertion Failure ....." (at run
time)
P.P.S: Everything else works just fine (without the use of "operator
+"
and "operator =" functions)

//code "tested" on Microsoft Visual C++ 6.0
#include <iostream>

using namespace std;

class DatArray {
public:
int rows, columns;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (DatArray da1); //problematic
Click to expand...


You've violated the "Rule of Three". Look it up. Also, consider
that operator = (the assignment op) should probably take a ref to
a const object instead of an object.
void operator ++ ();
//DatArray operator + (double d1); //does not work
};
[..]
Click to expand...

V
 
D

David Harmon

On 14 Mar 2007 11:05:35 -0700 in comp.lang.c++, "valerij"
How to write "operator +" and "operator =" functions in a class with
a defined constructor?
Click to expand...

operator+ should usually be

T operator+(T const & t1, T const & t2)
{
T result(t1);
result += t2;
return result;
}

operator= depends on the requirements of your class, but usually
you just use operator= of each of the base classes and members.
(That is the compiler supplied operator= if you do not write one,
but unfortunately you have to write += yourself.)

operator+= is a lot like operator= except using += instead of =.
All the = operators (if you need them) should be members.
//code "tested" on Microsoft Visual C++ 6.0
Click to expand...

Failure to upgrade to at least MSVC 7.x may be harmful to your sanity.
class DatArray {
public:
int rows, columns;
double **a;

DatArray::DatArray(int r, int c) {
Click to expand...

DatArray::DatArray(int r, int c)
/*DatArray DatArray::eek:perator + (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = a[c1][c2] + d1;
return *this;
}*/
Click to expand...

DatArray & DatArray::eek:perator += (double d1) {
for (int c1 = 0; c1 < a.size(); c1++)
for (int c2 = 0; c2 < a[c1].size(); c2++)
a[c1][c2] += d1;
return *this;
}
 
V

valerij

Yes, hi

How to write "operator +" and "operator =" functions in a class with
a defined constructor? The following code demonstrates that I don't
really understand how to do it... I think it has something to do with
the compiler calling the destructor twice. Could someone point out
where I go wrong?
P.S.: The error it gives is "Debug Assertion Failure ....." (at run
time)
P.P.S: Everything else works just fine (without the use of "operator
+"
and "operator =" functions)

//code "tested" on Microsoft Visual C++ 6.0
#include <iostream>

using namespace std;

class DatArray {
public:
int rows, columns;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (DatArray da1); //problematic
void operator ++ ();
//DatArray operator + (double d1); //does not work

};

DatArray::DatArray(int r, int c) {
int c1;
rows = r;
columns = c;
a = new double* [rows];
for (c1 = 0; c1 < rows; c1++) a[c1] = new double [columns];

}

DatArray::~DatArray() {
int c1;
for (c1 = 0; c1 < rows; c1++) delete [] a[c1];
delete [] a;

}

void DatArray::eek:perator = (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = d1;

}

void DatArray::eek:perator = (DatArray da1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = da1.a[c1][c2];

}

void DatArray::eek:perator ++ () {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2]++;

}

/*DatArray DatArray::eek:perator + (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = a[c1][c2] + d1;
return *this;

}*/

int main() {
int c1, c2;
DatArray myarray(3, 4), myarray2(3, 4);
myarray = 10.1;
for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray.a[c1][c2]
<< " ";
cout << endl;
}
cout << endl;
for (c1 = 0; c1 < 100; c1++) myarray++;
//myarray2 = myarray + 100; //this should be simpler, but does not
work ?!?!?!?!?!
myarray2 = myarray;
for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray2.a[c1][c2]
<< " ";
cout << endl;
}
cin.get(); //currently, after this, ERROR ... WHY?!?!?!?!?! (how to
fix this?!?!?!?!?)
return 0;}

//end of code "tested" on Microsoft Visual C++ 6.0

Thanks,
Valerij
Click to expand...

Hi again,

I seem to have figured it out. You have to use pointers. The working
code is below. My next question is how to implement the following:

DatArray* operator + (DatArray da1);

Thanks,
Valerij

//code tested on Microsoft Visual C++ 6.0
#include <iostream>

using namespace std;

class DatArray {
public:
int rows, columns;
int name;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (int i1);
void operator = (DatArray* da1);
DatArray* operator + (double d1);
DatArray* operator - (double d1);
DatArray* operator * (double d1);
DatArray* operator / (double d1);
void operator ++ ();
void operator -- ();
};

DatArray::DatArray(int r, int c) {
int c1;
rows = r;
columns = c;
a = new double* [rows];
for (c1 = 0; c1 < rows; c1++) a[c1] = new double [columns];
name = 0;
}

DatArray::~DatArray() {
int c1;
cout << "Destroying " << name << endl;
for (c1 = 0; c1 < rows; c1++) delete [] a[c1];
delete [] a;
}

void DatArray::eek:perator = (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = d1;
}

void DatArray::eek:perator = (int i1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = i1;
}

void DatArray::eek:perator = (DatArray* da1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = da1->a[c1][c2];
}

void DatArray::eek:perator ++ () {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2]++;
}

void DatArray::eek:perator -- () {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2]--;
}

DatArray* DatArray::eek:perator + (double d1) {
int c1, c2;
DatArray *da1;
da1 = new DatArray(rows, columns);
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) da1->a[c1][c2] = a[c1][c2] + d1;
return da1;
}

DatArray* DatArray::eek:perator - (double d1) {
int c1, c2;
DatArray *da1;
da1 = new DatArray(rows, columns);
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) da1->a[c1][c2] = a[c1][c2] - d1;
return da1;
}

DatArray* DatArray::eek:perator * (double d1) {
int c1, c2;
DatArray *da1;
da1 = new DatArray(rows, columns);
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) da1->a[c1][c2] = a[c1][c2] * d1;
return da1;
}

DatArray* DatArray::eek:perator / (double d1) {
int c1, c2;
DatArray *da1;
da1 = new DatArray(rows, columns);
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) da1->a[c1][c2] = a[c1][c2] / d1;
return da1;
}

int main() {
int c1, c2;
DatArray myarray(3, 4), myarray2(3, 4);

myarray.name = 1;
myarray2.name = 2;

myarray = 0;
myarray2 = 300;
myarray = myarray2 + 1000;
myarray2 = myarray / 100;

for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray.a[c1][c2]
<< " ";
cout << endl;
}
cout << endl;
for (c1 = 0; c1 < myarray.rows; c1++) {
for (c2 = 0; c2 < myarray.columns; c2++) cout << myarray2.a[c1][c2]
<< " ";
cout << endl;
}

return 0;
}
//end of code tested on Microsoft Visual C++ 6.0
 
V

valerij

valerij said:
Yes, hi
Click to expand...
How to write "operator +" and "operator =" functions in a class with
a defined constructor? The following code demonstrates that I don't
really understand how to do it... I think it has something to do with
the compiler calling the destructor twice. Could someone point out
where I go wrong?
P.S.: The error it gives is "Debug Assertion Failure ....." (at run
time)
P.P.S: Everything else works just fine (without the use of "operator
+"
and "operator =" functions)
Click to expand...
//code "tested" on Microsoft Visual C++ 6.0
#include <iostream>
Click to expand...
using namespace std;
Click to expand...
class DatArray {
public:
int rows, columns;
double **a;
DatArray(int r, int c);
~DatArray();
void operator = (double d1);
void operator = (DatArray da1); //problematic
Click to expand...

You've violated the "Rule of Three". Look it up. Also, consider
that operator = (the assignment op) should probably take a ref to
a const object instead of an object.
void operator ++ ();
//DatArray operator + (double d1); //does not work
};
[..]
Click to expand...

V
Click to expand...

OMG. I never heard of it ... just looking at it now ... this might
just be what i always wanted to know ...
thanks
 
V

valerij

On 14 Mar 2007 11:05:35 -0700 in comp.lang.c++, "valerij"
How to write "operator +" and "operator =" functions in a class with
a defined constructor?
Click to expand...

operator+ should usually be

T operator+(T const & t1, T const & t2)
{
T result(t1);
result += t2;
return result;
}

operator= depends on the requirements of your class, but usually
you just use operator= of each of the base classes and members.
(That is the compiler supplied operator= if you do not write one,
but unfortunately you have to write += yourself.)

operator+= is a lot like operator= except using += instead of =.
All the = operators (if you need them) should be members.
//code "tested" on Microsoft Visual C++ 6.0
Click to expand...

Failure to upgrade to at least MSVC 7.x may be harmful to your sanity.
class DatArray {
public:
int rows, columns;
double **a;
Click to expand...

std::vector said:
DatArray::DatArray(int r, int c) {
Click to expand...

DatArray::DatArray(int r, int c)
/*DatArray DatArray::eek:perator + (double d1) {
int c1, c2;
for (c1 = 0; c1 < rows; c1++)
for (c2 = 0; c2 < columns; c2++) a[c1][c2] = a[c1][c2] + d1;
return *this;
}*/
Click to expand...

DatArray & DatArray::eek:perator += (double d1) {
for (int c1 = 0; c1 < a.size(); c1++)
for (int c2 = 0; c2 < a[c1].size(); c2++)
a[c1][c2] += d1;
return *this;

}
Click to expand...

You see, I have Windows 98SE, so any higher and it will be just too
slow ;)
 
D

David Harmon

On 14 Mar 2007 12:50:26 -0700 in comp.lang.c++, "valerij"
You see, I have Windows 98SE, so any higher and it will be just too
slow ;)
Click to expand...

OK, that's a side issue. Don't neglect the part about getting rid of
the raw pointers and raw arrays. Prefer std::vector in application
level code.

Digital Mars C++ is very efficient under '98, and far more standard-
conforming than VC6. http://digitalmars.com
 

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