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Full Discussion: c++ assignment operator overloading
Top Forums Programming c++ assignment operator overloading Post 302481656 by Corona688 on Saturday 18th of December 2010 09:19:13 PM
Old 12-18-2010
Since the class doesn't know how much memory is allocated to mem, you can't. You have to store the size somewhere.

I'd do it like this:

Code:
#include <stdio.h>
#include <string.h>

class A {
public:
   int * mem;
   int size;
   A(int isize=0) : mem(NULL), size(0) {
      if(isize > 0)
      {
        mem=new int[isize];
        size=isize;
      }
   }

   A &operator=(const A &o)
   {
      if(size > 0) // Free existing memory
      {
         delete mem;
         size=0;
      }

      if(o.size > 0) // Copy other memory if it exists
      {
         mem = new int[o.size];
         size=o.size;
         memcpy(mem, o.mem, o.size * sizeof(int));
      }

      return(*this);
   }

  ~A() {
     if (mem!=NULL)
     {
       printf("Freeing %p\n", mem);
       delete mem;
     }
   }
};

int main(void)
{
    A a(100), b;

    b=a;
}

Last edited by Corona688; 12-18-2010 at 10:39 PM.. Reason: forgot the return statement
 

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LEARN ABOUT OPENSOLARIS

mem

mem(7D) 							      Devices								   mem(7D)

NAME

       mem, kmem, allkmem - physical or virtual memory access

SYNOPSIS

       /dev/mem

       /dev/kmem

       /dev/allkmem

DESCRIPTION

       The file /dev/mem is a special file that provides access to the physical memory of the computer.

       The  file  /dev/kmem  is  a special file that provides access to the virtual address space of the operating system kernel, excluding memory
       that is associated with an I/O device.

       The file /dev/allkmem is a special file that provides access to the virtual address space of the operating system kernel, including  memory
       that is associated with an I/O device.  You can use any of these devices to examine and modify the system.

       Byte  addresses	in  /dev/mem are interpreted as physical memory addresses. Byte addresses in /dev/kmem and /dev/allkmem are interpreted as
       kernel virtual memory addresses. A reference to a non-existent location returns an error. See ERRORS for more information.

       The file /dev/mem accesses physical memory; the size of the file is equal to the amount of physical memory in the computer. This  size  may
       be  larger  than 4GB on a system running the 32-bit operating environment. In this case, you can access memory beyond 4GB using a series of
       read(2) and write(2) calls, a pread64() or pwrite64() call, or a combination of llseek(2) and read(2) or write(2).

ERRORS

       EFAULT	 Occurs when trying to	write(2) a read-only location (allkmem), read(2) a write-only location (allkmem), or read(2) or write(2) a
		 non-existent or unimplemented location (mem, kmem, allkmem).

       EIO	 Occurs  when  trying  to  read(2) or write(2) a memory location that is associated with an I/O device using the /dev/kmem special
		 file.

       ENXIO	 Results from attempting to mmap(2) a non-existent physical (mem) or virtual (kmem, allkmem) memory address.

FILES

       /dev/mem        Provides access to the computer's physical memory.

       /dev/kmem       Provides access to the virtual address space of the operating system kernel, excluding memory that is  associated  with	an
		       I/O device.

       /dev/allkmem    Provides  access  to  the virtual address space of the operating system kernel, including memory that is associated with an
		       I/O device.

SEE ALSO

       llseek(2), mmap(2), read(2), write(2)

WARNINGS

       Using these devices to modify (that is, write to) the address space of a live running operating system or to modify  the  state	of	 a
       hardware  device  is  extremely	dangerous  and	may  result  in a system panic if kernel data structures are damaged or if device state is
       changed.

SunOS 5.11							    18 Feb 2002 							   mem(7D)
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