Pointer Aliases

Two pointers can refer to the same object, so writing through one pointer changes what the other reads.

alias Pointers alias when they store the same address.

shared object A write through one alias updates the single shared object.

                            value
                            value = 5 (default)value = 8value = 11
                        

                            pointer_aliases.c
                        
Replay: real traced execution (multi-file project)

                            #include <stdio.h>

int main(void) {
    int value = 5;
    int *left = &value;
    int *right = left;

    *right = *right + 1;

    printf("left=%d value=%d\n", *left, value);
    return 0;
}
#include <stdio.h>

int main(void) {
    int value = 8;
    int *left = &value;
    int *right = left;

    *right = *right + 1;

    printf("left=%d value=%d\n", *left, value);
    return 0;
}
#include <stdio.h>

int main(void) {
    int value = 11;
    int *left = &value;
    int *right = left;

    *right = *right + 1;

    printf("left=%d value=%d\n", *left, value);
    return 0;
}

                        
1value ← 5, left ← ⟨addr A⟩, right ← ⟨addr A⟩⋯3int main(void) {4    int value→ 5 = 5; //@value=8, 115    int *left→ ⟨addr A⟩ = &value5;6    int *right→ ⟨addr A⟩ = left⟨addr A⟩;78    *right⟨addr A⟩ = *right + 1;910    printf("left=%d value=%d\n", *left⟨addr A⟩, value6);11    return 0;12}⋯outputleft=6 value=6
1value ← 8, left ← ⟨addr A⟩, right ← ⟨addr A⟩⋯3int main(void) {4    int value→ 8 = 8;5    int *left→ ⟨addr A⟩ = &value8;6    int *right→ ⟨addr A⟩ = left⟨addr A⟩;78    *right⟨addr A⟩ = *right + 1;910    printf("left=%d value=%d\n", *left⟨addr A⟩, value9);11    return 0;12}⋯outputleft=9 value=9
1value ← 11, left ← ⟨addr A⟩, right ← ⟨addr A⟩⋯3int main(void) {4    int value→ 11 = 11;5    int *left→ ⟨addr A⟩ = &value11;6    int *right→ ⟨addr A⟩ = left⟨addr A⟩;78    *right⟨addr A⟩ = *right + 1;910    printf("left=%d value=%d\n", *left⟨addr A⟩, value12);11    return 0;12}⋯outputleft=12 value=12