Programs use many types of memory during operation, the most common of which are heap memory and stack memory. Here is a brief description of them and their purpose in the program:
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Stack Memory :
- When a function call occurs, the stack is used to store local variables, function parameters, and return addresses.
- The stack is a last-in-first-out (LIFO) structure, which means that as functions are called, new memory blocks are pushed onto the top of the stack, and when the function returns, these memory blocks are popped out.
- The size of the stack is limited, usually pre-allocated, and when you reach the upper limit of the stack (for example, due to a recursive call too deep), you will encounter a stack overflow.
- Memory allocation and deallocation is very fast on the stack because it only involves moving the stack pointer.
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Heap Memory :
- The heap is an area of memory used for dynamic memory allocation.
- When you use operators such as C
malloc()or C++newto dynamically allocate memory, these memory blocks are located on the heap. - Unlike the stack, the allocation and deallocation of heap memory may cause memory fragmentation and is relatively slow.
- Heap memory must be managed explicitly. If you allocate heap memory but forget to free it, it can cause a memory leak.
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Others :
- Static/global memory : This part of memory is used to store global variables and static variables. It exists throughout the life of the program.
- Code/Text Segment : Stores the executable code of the program.
- Data segment : stores global variables and static data in the program.
- Constant pool : In some languages (such as Java), there is a special area for storing constants, such as string literals.
Programs use all of the above types of memory during their execution. However, when we talk about a program's memory usage, we usually care about the stack and the heap, because these are the places where problems are most likely to occur (for example, stack overflows or memory leaks on the heap).