What is the difference between memory leak and memory overflow?

One Relevant concepts ：

out of memory （out of memory）： When a program requests memory , Not enough memory for it , appear out of memory; Like applying for a integer, But save it long Number that can be saved , That's memory overflow .

Memory leak （memory leak）： Refers to the program after applying for memory , Unable to free requested memory space , The harm of a memory leak can be ignored , But the memory leak has serious consequences , No matter how much memory , Sooner or later it will be taken up .

difference ： Memory overflow is when a program requests memory , Not enough memory for it , The system can no longer allocate the space you need ; Memory leak refers to the program after applying for memory , Unable to free requested memory space , The harm of a memory leak can be ignored , However, the number of memory leaks will lead to memory overflow .

Memory overflow is when you ask for more memory than the system can give you , The system can't meet the demand , So there's overflow .

A memory leak is when you apply to the system to allocate memory for use (new), But they don't return it after using it (delete), As a result, you can't access the memory you applied for （ Maybe you lost its address ）, And the system can't assign it again to the program it needs . A plate can only hold 4 A fruit , You put on 5 individual , As a result, I fell to the ground and couldn't eat . This is overflow ！ Like stacks , When the stack is full, it will cause space overflow , Call for overflow , When the stack is empty, it will cause space overflow , It's called underflow . The memory allocated is not enough to put down the sequence of data items , It's called a memory overflow .

Classify in the way that they happen , Memory leaks can be divided into 4 class ：

1、 Frequent memory leaks . Code with memory leaks will be executed multiple times to , Each time it is executed, it will cause a memory leak .

2、 Occasional memory leak . Code that has a memory leak only happens under certain circumstances or operating procedures . Recurrent and episodic are relative . For a particular environment , What happens occasionally may become what happens frequently . So test environment and test method are very important to detect memory leak .

3、 One time memory leak . Code with a memory leak will only be executed once , Or because of algorithm flaws , There will always be a single memory leak . such as , Allocate memory in the class's constructor , In the destructor, the memory is not freed , So memory leaks only happen once .

4、 Implicit memory leaks . Program in the process of running the allocation of memory , But don't release memory until the end . Strictly speaking, there is no memory leak , Because eventually the program frees up all of the requested memory . But for a server program , It takes a few days to run , Weeks or even months , Not releasing memory in time can also lead to the eventual exhaustion of all the system's memory . therefore , We call such memory leaks implicit memory leaks .

From the point of view of the user using the program , Memory leaks themselves don't do any harm , As a general user , There is no memory leak at all . The real danger is the accumulation of memory leaks , This will eventually consume all the memory of the system . From this perspective , One time memory leaks don't hurt , Because it doesn't pile up , The implicit memory leak is very harmful , Because it is more difficult to detect than frequent and accidental memory leaks