Structs

I'm having some issues with structs.

If I have a couple of nested structs, is it possible to obtain the address of a member struct, or is this something that is not good practise. I.e. is it possible to obtain the address of fooStruct->barStruct->num ?. I am guessing that this is not possible, as the member would be something like an offset from the address of the encompassing struct (maybe??).

Code:

---

#include <iostream>

using namespace std;

typedef struct bar
{
        int num;
}BAR;

typedef struct foo
{
        BAR *barStruct;
}FOO;

int main(void)
{
        FOO *fooStruct = new FOO;
        fooStruct->barStruct = new BAR;

        FOO *blahStruct = new FOO;
        blahStruct->barStruct = new BAR;

        fooStruct->barStruct->num = 10;
        blahStruct->barStruct->num = 11;

        cout << "fooStruct->barStruct->num: " << fooStruct->barStruct->num << endl;
        cout << "blahStruct->barStruct->num: " << blahStruct->barStruct->num << endl;

        return 0;
}

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Also, if I do not allocate memory for barStruct member in both of the "fooStruct" and "blahStruct" then the "num" member seems to point at exactly the same location. I.e. updating one with a value changes the other. Why is this?

>> is it possible to obtain the address of fooStruct->barStruct->num ?

Yes. &( fooStruct->barStruct->num )


>>Also, if I do not allocate memory for barStruct member in both of the "fooStruct" and "blahStruct" then the "num" member seems to point at exactly the same location. I.e. updating one with a value changes the other. Why is this?
It is undefined behaviour, so anything can happen.

Quote:

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Originally posted by filler_bunny
I'm having some issues with structs.

If I have a couple of nested structs, is it possible to obtain the address of a member struct, or is this something that is not good practise. I.e. is it possible to obtain the address of fooStruct->barStruct->num ?.

---

Sure; you can take the address of anything that lives in memory.

I am guessing that this is not possible, as the member would be

Quote:

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Also, if I do not allocate memory for barStruct member in both of the "fooStruct" and "blahStruct" then the "num" member seems to point at exactly the same location. I.e. updating one with a value changes the other. Why is this?

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At a guess? Coincidence. Dereferencing a pointer to unallocated memory is undefined; for the results you see, it's likely that, under the test conditions you had, the initial value for fooStruct->barStruct and blahStruct->barStruct was the same -- that is, they point at the same (uninitialized) place in memory.

Quote:

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Yes. &( fooStruct->barStruct->num )

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That simple huh. :)

Thanks for the responses, that is very helpful!