Stack and heap

This page deliberately lives several folders deep. The filesystem is the note tree; no second navigation database is involved.

notes/
└── systems/
    └── memory/
        └── stack-and-heap.md

Tags cut across that tree. The hierarchy answers where does this note belong? while tags such as #c and #memory answer what else is it related to?

Working model

Region	Usually contains	Lifetime
Stack	Call frames, parameters, automatic variables	Until the function returns
Heap	Dynamically allocated objects	Until explicitly released or reclaimed

The names describe allocation strategies, not C types. A pointer variable can live on the stack while referring to an object on the heap.

#include <stdlib.h>

int *make_value(void) {
    int *value = malloc(sizeof *value);
    if (value != NULL) *value = 42;
    return value;
}

The pointer variable value is automatic; the allocation returned by malloc remains alive after the function returns and must later be passed to free.