← Back to Blog

Understanding Pointers and Memory Management in C

SystemsC

Pointers are the barrier to entry for C. They scare away the faint of heart. But a pointer is just a variable that holds a memory address. That’s it.

Stack vs. Heap

To understand pointers, you must understand memory layout.

The Stack

Fast, ordered, automatic. Variables created here die when the function returns.

void foo() {
    int a = 10; // 'a' lives on the stack
} // 'a' is destroyed here

The Heap

An endless ocean of memory. You ask for a chunk, you get it. But you must give it back.

void foo() {
    int* ptr = malloc(sizeof(int)); // Request 4 bytes
    *ptr = 10;
    // ...
    free(ptr); // You MUST free it!
}

The “Segfault” (Segmentation Fault)

This happens when you try to touch memory that doesn’t belong to you.

1. Dereferencing NULL: int* p = NULL; *p = 5; -> CRASH.
2. Use After Free: You free(ptr) but then try to read *ptr. The OS has likely revoked your access card or given that room to someone else.

Why Learn This?

“I use Java/Python, I don’t need this.”

Yes, you do. When your Java app throws an OutOfMemoryError, or your Python script runs slow because of unintentional object copying, understanding what’s happening under the hood (on the heap) allows you to fix it. Abstractions are leaky; knowing the basement mechanics makes you a better architect of the skyscraper.

← Back to Blog