Apprendre Defensive Programming Principles | Writing Safe and Predictable Code

Prérequis

C Basics

Definition

Defensive programming is the practice of writing code that anticipates errors, validates assumptions, and ensures that failures happen in a controlled and predictable way.

In C you should never assume that inputs are always valid or that functions always succeed. Instead, you write your code to check for unexpected or invalid situations, so your program can handle them safely and avoid unpredictable behavior or crashes. This approach leads to more robust and reliable software, especially in a language like C where the consequences of mistakes can be severe.

main.c


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#include <stdio.h>

// Non-defensive version: assumes input is always valid (denominator != 0)
double divide(int numerator, int denominator) {
    return (double)numerator / denominator;
}

int main() {
    int num = 10;
    int denom = 0;

    printf("Non-defensive result: %f\n", divide_nondefensive(num, denom)); // Undefined behavior

    return 0;
}

Assuming inputs are always valid is risky in C. Without checks for invalid values, like zero division or out of bounds access, your program can crash or behave unpredictably. Defensive checks validate inputs and keep your code safe and reliable.

main.c


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#include <stdio.h>

// Defensive version: checks for invalid input (denominator == 0)
double divide_defensive(int numerator, int denominator) {
    if (denominator == 0) {
        printf("Error: division by zero.\n");
        return 0.0; // Or handle error as appropriate
    }
    return (double)numerator / denominator;
}

int main() {
    int num = 10;
    int denom = 0;

    printf("Defensive result: %f\n", divide_defensive(num, denom)); // Safe handling

    return 0;
}

This is just a simple example of defensive programming in action. In real-world C programs, there are many more scenarios where careful validation, error checking, and safe coding practices are essential to ensure reliability and prevent serious bugs or crashes.

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Section 1. Chapitre 1

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Prérequis

C Basics

Definition

Defensive programming is the practice of writing code that anticipates errors, validates assumptions, and ensures that failures happen in a controlled and predictable way.

main.c


              123456789101112131415
            
#include <stdio.h>

// Non-defensive version: assumes input is always valid (denominator != 0)
double divide(int numerator, int denominator) {
    return (double)numerator / denominator;
}

int main() {
    int num = 10;
    int denom = 0;

    printf("Non-defensive result: %f\n", divide_nondefensive(num, denom)); // Undefined behavior

    return 0;
}

main.c


              12345678910111213141516171819
            
#include <stdio.h>

// Defensive version: checks for invalid input (denominator == 0)
double divide_defensive(int numerator, int denominator) {
    if (denominator == 0) {
        printf("Error: division by zero.\n");
        return 0.0; // Or handle error as appropriate
    }
    return (double)numerator / denominator;
}

int main() {
    int num = 10;
    int denom = 0;

    printf("Defensive result: %f\n", divide_defensive(num, denom)); // Safe handling

    return 0;
}

Tout était clair ?

Merci pour vos commentaires !

Section 1. Chapitre 1