Processes and Memory Organisation

CODE(静态存储区域)

Also known as the TEXT Segment

Usually starts at or near address 0 and does not change size during the lifetime of the process

Contains:

the machine instructions for the problem

STACK

Used to pass data between functions, and to store temporary variables local to a given routine

The stack often starts at a very high address and grows torwards smaller addresses (this may seem to waste a large amount of space. However, it does not, because the use of virtual memory means that unused addresses below the stack do not need to be mapped in memory)

HEAP

Dynamic memory which allocated by the process at run time(the most complicated type of memory)

Usually allocated starting just beyond the end of the code segment, and grows up in memory towards the stack

The end of heap is sometimes called the process break point (usually using malloc()/free() to manage this task)

Stack vs Heap Pros and Cons

Stack

very fast access

don’t have to explicitly de-allocate variables

space is managed efficiently by CPU, memory will not become fragmented

local variables only

limit on stack size (OS-dependent)

variables cannot be resized

Heap

variables can be accessed globally

no limit on memory size

(relatively) slower access

no guaranteed efficient use of space, memory may become fragmented overtime as blocks of memory are allocated, then freed

you must manage memory (you’re in charge of allocating and freeing variables)

variables can be resized using realloc()