cheap-memorydynamic-memory-allocationstack-memorystatic-allocation

Are variables on the stack "statically allocated"?

I was reading this article and saw this: "This article assumes that you already know and understand at least basically how the memory map in GNU/Linux system works, and specially the difference between memory statically allocated in the stack and memory dynamically allocated in the heap."

This confused me because I thought that stack and heap are dynamically allocated, meaning only allocated if necessary, and global variables and variables declared as "static" inside of a function are statically allocated, meaning always allocated.

For example, if I have

void f() {
    int x = 1;
    ...
}

the value 1 only gets put on the stack and the stack pointer only gets incremented if the function f() gets called. Likewise, if I have

void f() {
    int x = malloc(1 * sizeof(int));
    ...
}

that heap memory only gets allocated if f() is called. However, if I have "int x = 1;" in the global section of the program or "static int x = 1;" within a function body, any time I run this program, that memory will be allocated in the data section with the value 1.

Am I wrong about any of this?

Solution

  • The stack itself is statically allocated. Variables allocated in the stack come and go, as control flow enters and leaves their scope.