Here is simple C program which prints some addresses
#include <stdio.h>
#include <stdlib.h>
struct thing {
int a;
int b;
};
int main(void)
{
struct thing t1, t2, *t3, *t4;
printf(" t1 @ %p\n", &t1);
printf(" t2 @ %p\n", &t2);
printf(" t3 @ %p\n", &t3);
printf(" t4 @ %p\n", &t4);
t3 = calloc(1, sizeof(struct thing));
t4 = calloc(1, sizeof(struct thing));
printf("*t3 @ %p\n", t3);
printf("*t4 @ %p\n", t4);
}
Run
Output:
t1 @ 0x7ffcbecee138
t2 @ 0x7ffcbecee140
t3 @ 0x7ffcbecee128
t4 @ 0x7ffcbecee130
*t3 @ 0x56153fdc16b0
*t4 @ 0x56153fdc16d0
Run
>From the output I clearly see that all 4 variables are on the stack and `t3,
>t4` points somewhere into the heap (addresses with lower values). Then I tried
>to write something similar in Nim:
from strutils import toHex, strip
proc printAddr(p: pointer) =
let u = cast[uint64](p)
echo "0x", u.toHex.strip(leading = true, trailing = false, chars = {'0'})
type
Thing = object
a: int
b: int
var
t1 = Thing(a: 1, b: 2) # on the stack
t2 = Thing(a: 3, b: 4) # on the stack
t3, t4: ref Thing # on the heap
printAddr(t1.addr)
printAddr(t2.addr)
t3 = new(Thing)
t4 = new(Thing)
echo t3.repr
echo t4.repr
Run
Output:
0x55F7A66C3060
0x55F7A66C3070
ref 0x7f7e3c893050 --> [a = 0, b = 0]
ref 0x7f7e3c893070 --> [a = 0, b = 0]
Run
First two addresses seem to belong to the heap, aren't they? I expected them to
be in the stack region. Second two other way around... If these are addresses
of `t3, t4` (which are on the stack), then how to print locations where the
objects seat?
