Lære Safe Handling of Pointers | Writing Safe and Predictable Code

Pointers are variables that store the memory address of another variable. They are powerful in C because they allow you to directly access and manipulate memory. However, pointers are also risky: improper use can lead to bugs such as crashes, memory corruption, or unpredictable program behavior. One common source of errors is dereferencing a pointer that does not point to a valid memory location.

main.c


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#include <stdio.h>

int main() {
    int *unsafe_ptr = NULL; // This pointer is NULL

    // Unsafe: Dereferencing a NULL pointer (will likely crash)
    printf("%d\n", *unsafe_ptr); // Causes undefined behavior

    return 0;
}

This first example shows what happens when you dereference a NULL pointer — it leads to undefined behavior and often crashes the program. Look at a safer version that includes proper checks before using pointers.

main.c


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#include <stdio.h>

int main() {
    int value = 42;
    int *safe_ptr = &value;   // Valid pointer
    int *unsafe_ptr = NULL;   // NULL pointer

    // Safe: Check for NULL before dereferencing safe_ptr
    if (safe_ptr != NULL)
        printf("Safe pointer value: %d\n", *safe_ptr);
    else
        printf("safe_ptr is NULL\n");

    // Safe: Check for NULL before dereferencing unsafe_ptr
    if (unsafe_ptr != NULL)
        printf("Unsafe pointer value: %d\n", *unsafe_ptr);
    else
        printf("unsafe_ptr is NULL\n");

    return 0;
}

Note

Always check whether a pointer is NULL before dereferencing it. This simple defensive check prevents crashes and helps you identify logic errors early, keeping your programs more stable and predictable.

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main.c


              12345678910
            
#include <stdio.h>

int main() {
    int *unsafe_ptr = NULL; // This pointer is NULL

    // Unsafe: Dereferencing a NULL pointer (will likely crash)
    printf("%d\n", *unsafe_ptr); // Causes undefined behavior

    return 0;
}

main.c


              123456789101112131415161718192021
            
#include <stdio.h>

int main() {
    int value = 42;
    int *safe_ptr = &value;   // Valid pointer
    int *unsafe_ptr = NULL;   // NULL pointer

    // Safe: Check for NULL before dereferencing safe_ptr
    if (safe_ptr != NULL)
        printf("Safe pointer value: %d\n", *safe_ptr);
    else
        printf("safe_ptr is NULL\n");

    // Safe: Check for NULL before dereferencing unsafe_ptr
    if (unsafe_ptr != NULL)
        printf("Unsafe pointer value: %d\n", *unsafe_ptr);
    else
        printf("unsafe_ptr is NULL\n");

    return 0;
}

Note

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