Question

Correction:

I messed up with the concept of pointer address and the address the pointer points to, so the following code has been modified. And now it prints out what I want, variable a, c, i, j, k, p are on the stack, and variable b,d are on the heap. Static and global variables are on another segment. Thanks a lot for all of you!

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Well, I know that these two concepts are deeply discussed…but I still have questions for the following code:

#include <iostream>
using namespace std;

class A {

};

int N = 10;

void f(int p) {
    int j = 1;
    float k = 2.0;
    A c;
    A* d = new A();
    static int l = 23;
    static int m = 24;
    cout << "&c: " << &c << endl;
    cout << "&d: " << d << endl;
    cout << "&j: " << &j << endl;
    cout << "&k: " << &k << endl;
    cout << "&l: " << &l << endl;
    cout << "&m: " << &m << endl;
    cout << "&p: " << &p << endl;
}

int main() {
    int i = 0;
    A* a;
    A* b = new A();
    cout << "&a: " << &a << endl;
    cout << "&b: " << b << endl;
    cout << "&i: " << &i << endl;
    cout << "&N: " << &N << endl;
    f(10);
    return 0;
}

My result is:

&a: 0x28ff20
&b: 0x7c2990
&i: 0x28ff1c
&N: 0x443000
&c: 0x28fef3
&d: 0x7c0f00
&j: 0x28feec
&k: 0x28fee8
&l: 0x443004
&m: 0x443008
&p: 0x28ff00

This is pretty interesting, coz except the global variable N, and two static variables in function f, which are l and m, the addresses of all the other variables seem to be together. (Note: The code and the results have been modified and not corresponding to what is said here.)

I’ve searched a lot about stack and heap. The common sense is that, if an object is created by “new”, then it is on the heap. And local variables (such as j and k in the above sample) are on stack. But it seems not to be the case in my example. Does it depend on different compilers, or my understanding is wrong?

Thanks a lot for all of you.

Answer 1

Your understanding is wrong. For example, b is a pointer – if you want the address of the object created by new, you need to print out b, not &b. b is a local variable, so it itself (found at &b) is on the stack.

For your example, N, l, and m are presumably somewhere in your executable’s data section. As you can see, they have similar addresses. Every other variable you are printing out is on the stack – their addresses are likewise similar to one another. Some of them are pointers pointing to objects allocated from the heap, but none of your printouts would show that.