Destructor question

[petermichaux]

Hi,

I ran into a destructor problem that is illustrated in the following code. I have used a stripped down matrix class. The problem is the destructor is invoked when the function testfunc ends. I think the destructor deallocates the memory pointed to by secondmatrix.p. That also means the memory pointed to by firstmatrix.p is deallocated. How do I avoid this so I can continue using firstmatrix later in main.

Thanks,
Peter

// - - - - - - - - - main.cpp - - - - - - - - - - - - 

#include <stdlib.h>
#include "matrix.h"

using namespace std;

void testfunc(matrix secondmatrix){
     //doesn't matter what happens in here
}

int main(void) {

    matrix firstmatrix(4,5);
    testfunc(firstmatrix);    

    //at this point isn't the memory pointed to by firstmatrix.p gone?
 
    system("PAUSE");	
    return 0;
}

// - - - - - - - - - matrix.h - - - - - - - - - - - - 

#ifndef MAT_H
#define MAT_H

using namespace std;

class matrix {
public:
    matrix(){;} 
    matrix(long,long);           
    ~matrix(){delete [] p;} 
               
protected:
    double *p;
    long r; /*number of rows*/
    long c; /*number of columns*/
};

#endif

// - - - - - - - - - - matrix.cpp - - - - - - - - - - - 

#include <assert.h>
#include "matrix.h"

using namespace std;

matrix::matrix(long rows, long cols){
    r = rows;
    c = cols;
        
    p = new double [rows*cols];
    assert (p != 0);
}