Problem with double matrix in vc++ Express edition

[Nangi]

Hi, I've got a problem with this code.

I've got a double Matrix A and a vector b, initialized with

DoubleMatr A = new double*[3];
DoubleVect b = new double[3];

where DoubleMatr and DoubleVect are defined as

typedef double* DoubleVect;
typedef double** DoubleMatr;

then i pass the matrix and the vector to a function

void CreateSystemFromPolygon(Polygon *p, double *X, double *Y,
DoubleMatr A, DoubleVect b)
....
for ( int i = 0 ; i < 3 ; i++)
{
for (int j = 0 ; j < 3; j++)
{
A[i][j] = 0;
}

b[i] = 0.0;
}

A[0][0] = 1.0;
A[1][1] = 1.0;

b[0] = X[0];
b[1] = Y[0];
....

at runtime i watch the values of A[0][0] A[0][1] etc..
I see that the istruction A[0][0] = 1.0 modify A[0][0] but A[1][0] and
A[2][0] too.
Where is the problem?

[David Wilkinson]

Nangi wrote:

Hi, I've got a problem with this code.

I've got a double Matrix A and a vector b, initialized with

DoubleMatr A = new double*[3];
DoubleVect b = new double[3];

where DoubleMatr and DoubleVect are defined as

typedef double* DoubleVect;
typedef double** DoubleMatr;

then i pass the matrix and the vector to a function

void CreateSystemFromPolygon(Polygon *p, double *X, double *Y,
DoubleMatr A, DoubleVect b)
...
for ( int i = 0 ; i < 3 ; i++)
{
for (int j = 0 ; j < 3; j++)
{
A[i][j] = 0;
}

b[i] = 0.0;
}

A[0][0] = 1.0;
A[1][1] = 1.0;

b[0] = X[0];
b[1] = Y[0];
...

at runtime i watch the values of A[0][0] A[0][1] etc..
I see that the istruction A[0][0] = 1.0 modify A[0][0] but A[1][0] and
A[2][0] too.
Where is the problem?

Nanji:

You have not defined a two-dimensional double array. You have just
defined an array of 3 double pointers. A[0], for example is a pointer to
double, but it is not pointing at anything. You need to do

A[0] = new double[3];
A[1] = new double[3];
A[2] = new double[3];

--
David Wilkinson
Visual C++ MVP

[Nangi]

On 21 Dic, 03:39, David Wilkinson <[e-mail]:

Nangi wrote:

Hi, I've got a problem with this code.

I've got a double Matrix A and a vector b, initialized with

* *DoubleMatr A = new double*[3];
* *DoubleVect b = new double[3];

where DoubleMatr and DoubleVect are defined as

typedef double* DoubleVect;
typedef double** DoubleMatr;

then i pass the matrix and the vector to a function

void CreateSystemFromPolygon(Polygon *p, double *X, double *Y,
DoubleMatr A, DoubleVect b)
...
* *for ( int i = 0 ; i < 3 ; i++)
* *{
* * * * * *for (int j = 0 ; j < 3; j++)
* * * * * *{
* * * * * * * * * *A[i][j] = 0;
* * * * * *}

* * * * * *b[i] = 0.0;
* *}

* *A[0][0] = 1.0;
* *A[1][1] = 1.0;

* *b[0] = X[0];
* *b[1] = Y[0];
...

at runtime i watch the values of A[0][0] A[0][1] etc..
I see that the istruction A[0][0] = 1.0 modify A[0][0] but A[1][0] and
A[2][0] too.
Where is the problem?

Nanji:

You have not defined a two-dimensional double array. You have just
defined an array of 3 double pointers. A[0], for example is a pointer to
double, but it is not pointing at anything. You need to do

A[0] = new double[3];
A[1] = new double[3];
A[2] = new double[3];

--
David Wilkinson
Visual C++ MVP- Nascondi testo tra virgolette -

- Mostra testo tra virgolette -

Sorry, I forgot to post this part of code..

for ( int i = 0 ; i < 3 ; i++ ) A[i] = new double[3];

[Nangi]

On 21 Dic, 03:39, David Wilkinson <[e-mail]:

Nangi wrote:

Hi, I've got a problem with this code.

I've got a double Matrix A and a vector b, initialized with

* *DoubleMatr A = new double*[3];
* *DoubleVect b = new double[3];

where DoubleMatr and DoubleVect are defined as

typedef double* DoubleVect;
typedef double** DoubleMatr;

then i pass the matrix and the vector to a function

void CreateSystemFromPolygon(Polygon *p, double *X, double *Y,
DoubleMatr A, DoubleVect b)
...
* *for ( int i = 0 ; i < 3 ; i++)
* *{
* * * * * *for (int j = 0 ; j < 3; j++)
* * * * * *{
* * * * * * * * * *A[i][j] = 0;
* * * * * *}

* * * * * *b[i] = 0.0;
* *}

* *A[0][0] = 1.0;
* *A[1][1] = 1.0;

* *b[0] = X[0];
* *b[1] = Y[0];
...

at runtime i watch the values of A[0][0] A[0][1] etc..
I see that the istruction A[0][0] = 1.0 modify A[0][0] but A[1][0] and
A[2][0] too.
Where is the problem?

Nanji:

You have not defined a two-dimensional double array. You have just
defined an array of 3 double pointers. A[0], for example is a pointer to
double, but it is not pointing at anything. You need to do

A[0] = new double[3];
A[1] = new double[3];
A[2] = new double[3];

--
David Wilkinson
Visual C++ MVP- Nascondi testo tra virgolette -

- Mostra testo tra virgolette -

I've tried to run same code in Borland C++ Builder 2006.
THERE IS NO ERROR!

IS THIS A VC++ 2008 BUG?

[David Wilkinson]

Nangi wrote:

On 21 Dic, 03:39, David Wilkinson <[e-mail]:

>Nangi wrote:

>>Hi, I've got a problem with this code.
I've got a double Matrix A and a vector b, initialized with
� �DoubleMatr A = new double*[3];
� �DoubleVect b = new double[3];
where DoubleMatr and DoubleVect are defined as
typedef double* DoubleVect;
typedef double** DoubleMatr;
then i pass the matrix and the vector to a function
void CreateSystemFromPolygon(Polygon *p, double *X, double *Y,
DoubleMatr A, DoubleVect b)
...
� �for ( int i = 0 ; i < 3 ; i++)
� �{
� � � � � �for (int j = 0 ; j < 3; j++)
� � � � � �{
� � � � � � � � � �A[i][j] = 0;
� � � � � �}
� � � � � �b[i] = 0.0;
� �}
� �A[0][0] = 1.0;
� �A[1][1] = 1.0;
� �b[0] = X[0];
� �b[1] = Y[0];
...
at runtime i watch the values of A[0][0] A[0][1] etc..
I see that the istruction A[0][0] = 1.0 modify A[0][0] but A[1][0] and
A[2][0] too.
Where is the problem?

Nanji:

You have not defined a two-dimensional double array. You have just
defined an array of 3 double pointers. A[0], for example is a pointer to
double, but it is not pointing at anything. You need to do

A[0] = new double[3];
A[1] = new double[3];
A[2] = new double[3];

--
David Wilkinson
Visual C++ MVP- Nascondi testo tra virgolette -

- Mostra testo tra virgolette -

I've tried to run same code in Borland C++ Builder 2006.
THERE IS NO ERROR!

IS THIS A VC++ 2008 BUG?

Nanji:

Maybe the bug (if any) is in the debugger, not in the code generator.

--
David Wilkinson
Visual C++ MVP