Testing and Debugging

Boundary Check

An index check prevents the program from reading outside an array.

range guard The guard checks both lower and upper bounds before indexing.
fallback value The fallback path gives a predictable value for out-of-range input.

Boundary Check

index
boundary_check.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    int index = 1;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

#include <stdio.h>

int main(void) {
    int index = -1;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

#include <stdio.h>

int main(void) {
    int index = 3;
    int values[3] = {10, 20, 30};
    int selected = -1;

    if (index >= 0 && index < 3) {
        selected = values[index];
    }

    printf("selected=%d\n", selected);
    return 0;
}

  1. index ← 1, values ← ⟨addr A⟩, selected ← -1

    3int main(void) {4    int index→ 1 = 1; //@index=-1, 35    int values→ ⟨addr A⟩[3] = {10, 20, 30};6    int selected→ -1 = -1;

  2. selected ← 20

    8if (index1 >= 0 && index < 3) {9    selected→ 20 = values[index]20;10}

  3. printf("selected=%d ", selected);

    12    printf("selected=%d\n", selected20);13    return 0;14}
    outputselected=20

  1. index ← -1, values ← ⟨addr A⟩, selected ← -1

    3int main(void) {4    int index→ -1 = -1;5    int values→ ⟨addr A⟩[3] = {10, 20, 30};6    int selected→ -1 = -1;78    if (index >= 0 && index < 3) {9        selected = values[index];10    }1112    printf("selected=%d\n", selected-1);13    return 0;14}
    outputselected=-1

  1. index ← 3, values ← ⟨addr A⟩, selected ← -1

    3int main(void) {4    int index→ 3 = 3;5    int values→ ⟨addr A⟩[3] = {10, 20, 30};6    int selected→ -1 = -1;78    if (index >= 0 && index < 3) {9        selected = values[index];10    }1112    printf("selected=%d\n", selected-1);13    return 0;14}
    outputselected=-1