Help with dynamic memory

[Silver]

Hi everyone,

my program compiles and executes, but I get an error during run-time. I
guess it has something to do with memory allocation (which I don't seem to
fully control yet).. Here's the code:

#include <iostream>
#include <malloc.h>
#include <iomanip>
using namespace std;

class X;
class A
{
private:
float** ppa;
int fl;
int row1;
int column1;

public:
A(int n, int m); // Constructor
A(); // Default constructor
~A(); // Destructor
void setA(int n, int m);
void set_fl() {fl = 0;}

friend void multi(A &a, X &x);
};

A::A(int n, int m)
{
cout << endl << "Constructo r for class A called.";
fl = 1;
row1 = n;
column1 = n;

ppa = (float **)malloc(n * sizeof(float *));
for(int i = 0; i < n; i++)
ppa[i] = (float *)malloc(m * sizeof(float));
}

A::A()
{
cout << endl << "Default constructor for class A called.";
fl = 0;
}

A::~A()
{
if(fl)
{
free((void **)ppa);
cout << endl << "Destructor for class A called.";
}
}

void A::setA(int n, int m)
{
for (int i = 0; i < n; i++) // initialization of a[n][m]
{ // this is for a
for (int j = 0; j < m; j++)
{
cout << "\nDWSE TO STOIXEIO " << "a[" << i << "][" << j << "]";
cin >> ppa[i][j];
}
}
}

class X
{
private:
float* x;
float* b;
int row2;
int column2;
int fl;

public:
X(int n, int m);
~X();
void setX(int n, int m);
void set_fl() {fl = 0;}

friend void multi(A &a, X &x);
};

X::X(int n, int m)
{
cout << endl << "Constructo r for class X called.";
x = (float *)malloc(m * sizeof(float));
b = (float *)malloc(n * sizeof(float));
row2 = n;
column2 = 1;
}

X::~X()
{
if (fl=1)
{
free((void *)x);
free((void *)b);
}
cout << endl << "Destructor for class X called.";
}

void X::setX(int n, int m)
{
for (int i = 0; i < m; i++) // Initialization of b[m]
{
cout << "\nDWSE TO STOIXEIO " << "b[" << i << "]";
cin >> b[i];
}
}

void multi(A &a, X &x) // array multiplication
{
cout<<"\n\nMatr ix Multiplication\ n";
for(int i = 0; i < a.row1; i++)
{
x.b[i] = 0;
for (int k=0 ; k < x.row2; k++)
{
x.b[i] += a.ppa[i][k] * x.x[k];
}
cout << setw(5) << x.b[i] << endl;
}
a.set_fl();
x.set_fl();
}

int main()
{
int grammes = 0 ; // rows
int stiles = 0 ; // colums
int i = 0; // index for loop
int j = 0; // index for loop

cout << "PROGRAM FOR MATRIX MULTIPLICATION\ n";
cout << "---------------------------------\n\n";
cout << "\nROWS? ";
cin >> grammes;
cin.ignore(); // to get rid of newline

cout << "\nCOLUMNS? ";
cin >> stiles;
cin.ignore();

A a(grammes, stiles);
a.setA(grammes, stiles);

X x(grammes, stiles);
x.setX(grammes, stiles);

X b(grammes, stiles);

multi(a,x);

return 0;
}

[Gianni Mariani]

Re: Help with dynamic memory

Silver wrote:[color=blue]
> Hi everyone,
>
> my program compiles and executes, but I get an error during run-time. I
> guess it has something to do with memory allocation (which I don't seem to
> fully control yet).. Here's the code:
>
> #include <iostream>
> #include <malloc.h>
> #include <iomanip>
> using namespace std;
>
> class X;
> class A
> {
> private:
> float** ppa;
> int fl;[/color]

What is "fl" ?
[color=blue]
> int row1;
> int column1;
>
> public:
> A(int n, int m); // Constructor
> A(); // Default constructor
> ~A(); // Destructor
> void setA(int n, int m);
> void set_fl() {fl = 0;}
>
> friend void multi(A &a, X &x);
> };
>
> A::A(int n, int m)
> {
> cout << endl << "Constructo r for class A called.";
> fl = 1;
> row1 = n;
> column1 = n;
>
> ppa = (float **)malloc(n * sizeof(float *));[/color]

use new. Or even better - use std::vector<flo at>
[color=blue]
> for(int i = 0; i < n; i++)
> ppa[i] = (float *)malloc(m * sizeof(float));
> }
>
> A::A()
> {
> cout << endl << "Default constructor for class A called.";
> fl = 0;
> }
>
> A::~A()
> {
> if(fl)
> {
> free((void **)ppa);
> cout << endl << "Destructor for class A called.";
> }[/color]

you can use ppa instead of fl ...
[color=blue]
> }
>
> void A::setA(int n, int m)
> {
> for (int i = 0; i < n; i++) // initialization of a[n][m]
> { // this is for a
> for (int j = 0; j < m; j++)
> {
> cout << "\nDWSE TO STOIXEIO " << "a[" << i << "][" << j << "]";
> cin >> ppa[i][j];
> }
> }
> }
>
> class X
> {
> private:
> float* x;
> float* b;
> int row2;
> int column2;
> int fl;
>
> public:
> X(int n, int m);
> ~X();
> void setX(int n, int m);
> void set_fl() {fl = 0;}[/color]

Look up "the c++ rule of 3".

See references to th "Rule of 3": if your class has either a destructor
or a copy constructor or an assignment operator, it probably needs all 3
of them.
[color=blue]
>
> friend void multi(A &a, X &x);
> };
>
> X::X(int n, int m)
> {
> cout << endl << "Constructo r for class X called.";
> x = (float *)malloc(m * sizeof(float));
> b = (float *)malloc(n * sizeof(float));[/color]

use a std::vector.
[color=blue]
> row2 = n;
> column2 = 1;
> }
>
> X::~X()
> {
> if (fl=1)
> {
> free((void *)x);
> free((void *)b);
> }
> cout << endl << "Destructor for class X called.";
> }
>
> void X::setX(int n, int m)
> {
> for (int i = 0; i < m; i++) // Initialization of b[m]
> {
> cout << "\nDWSE TO STOIXEIO " << "b[" << i << "]";
> cin >> b[i];
> }
> }
>
> void multi(A &a, X &x) // array multiplication
> {
> cout<<"\n\nMatr ix Multiplication\ n";
> for(int i = 0; i < a.row1; i++)
> {
> x.b[i] = 0;
> for (int k=0 ; k < x.row2; k++)
> {
> x.b[i] += a.ppa[i][k] * x.x[k];
> }
> cout << setw(5) << x.b[i] << endl;
> }
> a.set_fl();
> x.set_fl();
> }
>
> int main()
> {
> int grammes = 0 ; // rows
> int stiles = 0 ; // colums
> int i = 0; // index for loop
> int j = 0; // index for loop
>
> cout << "PROGRAM FOR MATRIX MULTIPLICATION\ n";
> cout << "---------------------------------\n\n";
> cout << "\nROWS? ";
> cin >> grammes;
> cin.ignore(); // to get rid of newline
>
> cout << "\nCOLUMNS? ";
> cin >> stiles;
> cin.ignore();
>
> A a(grammes, stiles);
> a.setA(grammes, stiles);
>
> X x(grammes, stiles);
> x.setX(grammes, stiles);[/color]

setX initializes the "b" array but "multi" below uses the "x" array ....
[color=blue]
>
> X b(grammes, stiles);
>
> multi(a,x);
>
> return 0;
> }[/color]

suggestions:

a. Your memory allocation problem goes away when you use std::vector.
b. look up some other standard matrix library.