check pointer to class object for null value

[cPlusN00b]

This is jamming me up a little bit. I've been thru the tutorial on this site but the bit about null pointers I apparently don't get.. Thanks in advance for any advice and suggestions. I've already posted in the beginner forum but haven't got a response.

My question is.. lets say I have a pointer p_unit of type c_unit* (c_unit is an a.b.c.)
I have a function that returns a pointer to a new c_unit object:

c_unit * man_add_unit()
{
    c_unit * local_p_unit;
    unsigned short int local_run_code;
    print_man_add_menu();
    local_run_code = get_a_run_code(); // this bit just gets user input

    switch (local_run_code)
    {
    case 1:
        local_p_unit = add_matl_unit();
        break;
    case 2:
        local_p_unit = add_indy_unit();
        break;
    // ...
    }
    return local_p_unit;
}

I assign that to p_unit, then add it to a vector v_units:

p_unit = man_add_unit();
v_units.push_back(p_unit);
cout << "New unit added.\n";

The whole program runs on a loop, and another thing the user can do is to print out data on c_unit objects pointed to by v_units. The problem is, in that function up there ^ I give the user the option to go back to main menu without creating a unit.

Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.

I tried to make an if thing with
p_unit == 0
but this always returns false and doesn't catch the "bad" unit that will subsequently cause a crash. Can someone please point me in the right direction here?

Btw, I have considered assigning a reference to a generic c_unit object to that there local_p_unit so it won't return null, then remove pointers to that object from v_units at the end of the loop.. But I know there's got to be a better way.

Thanks for any help yall can give me
- cPlusN00b

[cPlusN00b]

bump?

[firedraco]

Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.

No, if you declare it an don't assign it anything it becomes garbage, not NULL. You'll have to initialize it yourself.

[Disch]

Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up).

In C and C++, values for built in types are not zero'd for you. If you do not initialize your variables, they are filled with whatever random garbage happened to be stored in memory. This is true of pointers as well.

So no. local_p_unit will not be null here, because you're never setting it to null.

p_unit == 0

This will work just fine if you have a null pointer. However as previously stated, you do not have a null pointer, which is why this is failing.

[cPlusN00b]

Ah so
Thanks guy, is all good now. Much appreciated.
Not sure why I didn't think to try that.. << derp!