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Segmentation Fault Fix

Fix 'Segmentation Fault' in Online C Compiler

Learn why segmentation faults happen in C and how to fix them — with clear explanations and working code examples.

segmentation-fault-fix

🧠 What is a Segmentation Fault in C?

A segmentation fault occurs when a program tries to access a memory area it shouldn't — for example, dereferencing an invalid pointer or accessing memory out of bounds.

🚨 Common Causes in Online C Compilers (and Fixes)

✅ 1. Uninitialized or NULL Pointer Dereference

int *ptr;
*ptr = 10;  // ❌ Segmentation Fault

Fix:

int *ptr = (int *)malloc(sizeof(int));
*ptr = 10;
printf("%d\n", *ptr);
free(ptr);

✅ 2. Array Index Out of Bounds

int arr[5];
arr[10] = 100;  // ❌ Invalid memory access

Fix:

int arr[5];
arr[4] = 100;  // ✅ Within valid range

✅ 3. Improper Use of scanf()

int num;
scanf("%d", num);  // ❌ Segmentation fault

Fix:

int num;
scanf("%d", &num);  // ✅ Correct usage

✅ 4. Using Freed Memory

int *ptr = malloc(sizeof(int));
free(ptr);
*ptr = 5;  // ❌ Illegal memory access

Fix: Avoid using ptr after freeing it, or set it to NULL.

✅ 5. Stack Overflow (Deep Recursion)

void recurse() {
    recurse();  // ❌ No base case leads to stack overflow
}

Fix:

void recurse(int count) {
    if (count <= 0) return;
    recurse(count - 1);
}

🛠️ How to Debug in Online C Compiler

  • Add printf() statements to check variable values.
  • Isolate the faulty block and test separately.
  • Use tools like Online C Compiler with input/output preview.
  • Avoid dynamic memory usage unless necessary.

💡 Pro Tip

Always initialize pointers and arrays properly, and double-check loops and input handling when using online compilers — they are more sensitive to runtime crashes due to limited memory.

✅ Conclusion

Segmentation faults are common, especially in C. But with careful pointer handling, bounds checking, and input validation, you can easily avoid them — even on an online compiler.

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