Memory Management in Depth

A running C program's memory splits into distinct regions: the stack (local variables, growing and shrinking automatically with function calls), the heap (malloced memory, managed entirely by hand), and static storage (global and static variables, allocated once for the program's whole lifetime).

int global = 1;             // static storage

void example(void) {
    int local = 2;           // stack — gone when example() returns
    static int persistent = 3; // static storage — keeps its value
    int *heap = malloc(sizeof(int)); // heap — lives until free()d
    *heap = 4;
    free(heap);
}

A static local variable retains its value between calls, unlike an ordinary local — useful for a counter that persists without needing a global variable visible to the whole file.

Common mistakes

• Returning a pointer to a local (stack) variable from a function — that memory is invalid the instant the function returns, even though the pointer itself still looks valid.