unable allocating memory

[Mona]

class myPoly
{
private:
int nv;
double *x, *y;
int *p;

public:
myPoly()
{
x = new double (0);
y = new double (0);
p = new int (0);
nv = 0;
}

myPoly(int n) // number of vertices
{
nv = n;
}

~myPoly()
{
delete x;
delete y;
delete p;
}

void Draw()
{
Read("poly.dat" );
for ( int k = 0; k<nv ; k++)
{
int p2 = abs(*p);
if (p2 == nv)
{
for (int l = 0; l<nv;l++)
{
if (*p>0)
{

glBegin(GL_LINE S);

glVertex2i(*x,* y);
}
}
glEnd();
}
}
}

void Read(const char s[]) // name of the datafile
{
ifstream infile;
infile.open(s);

int n_count;
double n_x,n_y;

infile>>n_count ; //how many vertices

for (int i = 0; i < n_count; i++)
{
myPoly(i);
infile>>n_x>>n_ y;
x = &n_x;
y = &n_y;
}
for (int j = 0; j< n_count ; j++)
{
infile >>p[j];
}
infile.close();
}
}

this is my class, and I wonder how come my pointer doesn't point to the
allocated memory?
the nv determines the allocation of memory of each x,y obtained from
the file.

[Richard Herring]

In message <11************ **********@l41g 2000cwc.googleg roups.com>, Mona
<pi*****@gmail. com> writes

class myPoly
{
private:
int nv;
double *x, *y;
int *p;

public:
myPoly()
{
x = new double (0);
y = new double (0);
p = new int (0);
nv = 0;
}

myPoly(int n) // number of vertices
{
nv = n;
Short answer: this constructor doesn't initialise x, y and p.

Long answer: there are other errors in your class design, which indicate
confusion about the diference between new/delete and new[]/delete[].
You'd be much better off using std::vector for this kind of thing.

[snip] }
this is my class, and I wonder how come my pointer doesn't point to the
allocated memory?
the nv determines the allocation of memory of each x,y obtained from
the file.

--
Richard Herring

[Mona]

well, I'm force to use classes and pointers because vector will slowing
the entire process.
So, I'm stuck in figuring out how to draw out the line.

[Stefan Näwe]

Mona schrieb:

well, I'm force to use classes and pointers because vector will slowing
the entire process.

How can you tell ?
Did you profile it ?

Stefan

[Mona]

Because this classes is only part of the whole code, and using vector
only makes us more reliable on c++ library.

[Stefan Näwe]

Mona schrieb:

Because this classes is only part of the whole code, and using vector
only makes us more
reliable on c++ library.

(You mean 'dependant on', right ?)

And going through all the hassle of doing the memory management yourself
is better ?

S.

[Richard Herring]

In message <11************ ********@f14g20 00cwb.googlegro ups.com>, Mona
<pi*****@gmail. com> writes

[please quote some context when replying, so we know what you're talking
about]

well, I'm force to use classes and pointers because vector will slowing
the entire process.
What makes you think so? How do you know?

What you are doing is what vector-based code would be doing anyway, but
with errors. There's no reason why using vector should be any slower.
So, I'm stuck in figuring out how to draw out the line.

--
Richard Herring

[Mona]

hm,....
depends on the task itself.
how large is the task i think, not really sure

[Mona]

Well, I try to discuss it but he requires me to use classes than
vector. Eventhough vector will be the easiest way to solve this problem.

[Richard Herring]

In message <11************ **********@l41g 2000cwc.googleg roups.com>, Mona
<pi*****@gmail. com> writes

[please quote some context when you reply]

Because this classes is only part of the whole code, and using vector
only makes us more reliable on c++ library.

Yes, the standard C++ library is reliable. Use it whenever you can.

--
Richard Herring