fork(): Child Memory from Parent

[bp4444]

On a HPUX, a CPP program. In main() defined a variable as int x = 900, called fork(), changed value of x as 89 in child process. Printed the address of x and value of x in child process and also in the parent process after wait(0).

Doubt
--------
Both in child and parent process, the address of x (&x) was same.
Since the address of x is same, the value shows different in parent and child.
Could you please reply. I got confused.


int main()
{

int x = 900;
int *ptr = &x;
cout << "\n &x x " <<&x<< " " << x; OUTPUT=> 0x7b03a490 900

if (fork())
{
cout << "\n &x x " <<&x<< " " << x; OUTPUT=> 0x7b03a490 900
wait(0);
cout << "\n walk up parent";
cout << "\n &x x " <<&x<< " " << x; OUTPUT=> 0x7b03a490 900
return(0);
}
else
{
x = 89;
cout << "\n &x x " <<&x<< " " << x; OUTPUT=> 0x7b03a490 89
exit(0);
}
cout << "\n parent is here exit";
return(0);
}

[mac11]

when you fork() each process gets it's own copy of everything. If you want to have the parent process see changes to variables that the child process makes (or vice-versa) you will have to use shared memory.

[bp4444]

when you fork() each process gets it's own copy of everything. If you want to have the parent process see changes to variables that the child process makes (or vice-versa) you will have to use shared memory.

My question is though the parent and child process print the same address (&x) of the variable x, shows different values in parent and child.

[JosAH]

My question is though the parent and child process print the same address (&x) of the variable x, shows different values in parent and child.

That's what virtual memory is all about; address 42 for your process doesn't
refer to the same real memory location as my process's address 42.

kind regards,

Jos