If a program tries to put too much information on the stack, stack overflow will occur. Note that there is generally a limit on the size of the stack – which can vary with the operating system (for example OSX currently has a default stack size of 8MB). Stack memory is divided into successive frames where each time a function is called, it allocates itself a fresh stack frame. The stack is a special region of memory, and automatically managed by the CPU – so you don’t have to allocate or deallocate memory. This leads to the “local” scope of function variables. Then when a function finishes running, all the variables associated with that function on the stack are deleted, and the memory they use is freed up. Every time a function declares a new variable it is “pushed” onto the stack. It’s a LIFO, “ L ast- I n,- F irst- O ut”, structure. The stack is used to store variables used on the inside of a function (including the main() function). For example, the same variable created inside a function using the static clause would allow it to be stored in static memory. It is also possible to force a variable to be static using the static clause. Inside a function the variable is allocated on the stack. Global variables are static, and there is only one copy for the entire program. If a variable is declared outside of a function, it is considered global, meaning it is accessible anywhere in the program. This memory can come from one of two places. On many systems this variable uses 4 bytes of memory. Static memory persists throughout the entire life of the program, and is usually used to store things like global variables, or variables created with the static clause. – heap: dynamic storage (large pool of memory, not allocated in contiguous order). – stack: local variable storage (automatic, continuous memory). – static: global variable storage, permanent for the entire run of the program. The great thing about C is that it is so intertwined with memory – and by that I mean that the programmer has quite a good understanding of “ what goes where“. C has three different pools of memory. AI will likely replace mediocre programmers.

Stack vs heap persistent