Where is heap

Also question is, where is the heap located? Stack is used for static memory allocation and Heap for dynamic memory allocation, both stored in the computer's RAM. Variables allocated on the stack are stored directly to the memory and access to this memory is very fast, and it's allocation is dealt with when the program is compiled.

Furthermore, how does a heap work? The definition of a heap is a complete binary tree in which the value stored in the parent is greater than or equal to that stored in each of its children.

Although a tree is used to explain how a heap works , the program uses an array to represent the heap. We exchange the root with the last node on the tree, c. A heap is a tree-based data structure in which all the nodes of the tree are in a specific order. For example , if is the parent node of , then the value of follows a specific order with respect to the value of and the same order will be followed across the tree.

The heap is a memory used by programming languages to store global variables. By default, all global variable are stored in heap memory space. It supports Dynamic memory allocation. The heap is not managed automatically for you and is not as tightly managed by the CPU. Heaps are used in many famous algorithms such as Dijkstra's algorithm for finding the shortest path, the heap sort sorting algorithm, implementing priority queues, and more.

Essentially, heaps are the data structure you want to use when you want to be able to access the maximum or minimum element very quickly. Is FIFO a heap? A heap data structure uses a complete binary tree. The heap property is that each node in a max-heap is greater than or equal to its children. What is the difference between a stack and a heap? Bondy Brian R. Bondy k gold badges silver badges bronze badges.

The pointer pBuffer and the value of b are located on the stack, and are mostly likely allocated at the entrance to the function.

Depending on the compiler, buffer may be allocated at the function entrance, as well. It is a common misconception that the C language, as defined by the C99 language standard available at open-std.

In fact, the word 'stack' does not even appear in the standard. See knosof. Brian You should explain why buffer[] and the pBuffer pointer are created on the stack and why pBuffer's data is created on the heap. I think some ppl might be confused by your answer as they might think the program is specifically instructing that memory be allocated on the stack vs heap but this is not the case.

Is it because Buffer is a value type whereas pBuffer is a reference type? Also the comments about scope and allocation are wrong - Scope is not connected to the stack or the heap at all. Variables on the heap must be destroyed manually and never fall out of scope. It's up to you or the garbage collector to free them.

Show 8 more comments. To what extent are they controlled by the OS or language runtime? David I don't agree that that is a good image or that "push-down stack" is a good term to illustrate the concept.

When you add something to a stack, the other contents of the stack aren't pushed down, they remain where they are. This answer includes a big mistake. Static variables are not allocated on the stack. See my answer [link] stackoverflow. Specifically, you say "statically allocated local variables" are allocated on the stack. Actually they are allocated in the data segment. Only automatically allocated variables which includes most but not all local variables and also things like function parameters passed in by value rather than by reference are allocated on the stack.

I've just realised you're right - in C, static allocation is its own separate thing rather than a term for anything that's not dynamic. I've edited my answer, thanks. It's not just C. Java, Pascal, Python and many others all have the notions of static versus automatic versus dynamic allocation. Saying "static allocation" means the same thing just about everywhere. In no language does static allocation mean "not dynamic". You want the term "automatic" allocation for what you are describing i.

I have moved this answer from another question that was more or less a dupe of this one. Both the stack and the heap are memory areas allocated from the underlying operating system often virtual memory that is mapped to physical memory on demand. In a multi-threaded environment each thread will have its own completely independent stack but they will share the heap. Concurrent access has to be controlled on the heap and is not possible on the stack.

The heap The heap contains a linked list of used and free blocks. New allocations on the heap by new or malloc are satisfied by creating a suitable block from one of the free blocks. This requires updating the list of blocks on the heap. This meta information about the blocks on the heap is also stored on the heap often in a small area just in front of every block. As the heap grows new blocks are often allocated from lower addresses towards higher addresses. Thus you can think of the heap as a heap of memory blocks that grows in size as memory is allocated.

If the heap is too small for an allocation the size can often be increased by acquiring more memory from the underlying operating system. Allocating and deallocating many small blocks may leave the heap in a state where there are a lot of small free blocks interspersed between the used blocks. A request to allocate a large block may fail because none of the free blocks are large enough to satisfy the allocation request even though the combined size of the free blocks may be large enough.

This is called heap fragmentation. When a used block that is adjacent to a free block is deallocated the new free block may be merged with the adjacent free block to create a larger free block effectively reducing the fragmentation of the heap.

The stack The stack often works in close tandem with a special register on the CPU named the stack pointer. Initially the stack pointer points to the top of the stack the highest address on the stack. The CPU has special instructions for pushing values onto the stack and popping them off the stack. Each push stores the value at the current location of the stack pointer and decreases the stack pointer. A pop retrieves the value pointed to by the stack pointer and then increases the stack pointer don't be confused by the fact that adding a value to the stack decreases the stack pointer and removing a value increases it.

Remember that the stack grows to the bottom. The values stored and retrieved are the values of the CPU registers. If a function has parameters, these are pushed onto the stack before the call to the function.

The code in the function is then able to navigate up the stack from the current stack pointer to locate these values. When a function is called the CPU uses special instructions that push the current instruction pointer onto the stack, i.

The CPU then jumps to the function by setting the instruction pointer to the address of the function called. Later, when the function returns, the old instruction pointer is popped off the stack and execution resumes at the code just after the call to the function. When a function is entered, the stack pointer is decreased to allocate more space on the stack for local automatic variables. If the function has one local 32 bit variable four bytes are set aside on the stack. When the function returns, the stack pointer is moved back to free the allocated area.

Nesting function calls work like a charm. Each new call will allocate function parameters, the return address and space for local variables and these activation records can be stacked for nested calls and will unwind in the correct way when the functions return. Often the memory area used for the stack is set up in such a way that writing below the bottom the lowest address of the stack will trigger a trap or exception in the CPU.

This exceptional condition can then be caught by the runtime and converted into some kind of stack overflow exception. Can a function be allocated on the heap instead of a stack?

Maggyero 3, 3 3 gold badges 24 24 silver badges 45 45 bronze badges. Martin Liversage Martin Liversage Every reference type is composition of value types int, string etc. As it is said, that value types are stored in stack than how does it work when they are part of reference type.

This answer was the best in my opinion, because it helped me understand what a return statement really is and how it relates to this "return address" that I come across every now and then, what it means to push a function onto the stack, and why functions are pushed onto stacks. Great answer! What do you mean "The code in the function is then able to navigate up the stack from the current stack pointer to locate these values. Can you elaborate on this please? Show 12 more comments. More information can be found here: The difference between stack and heap memory allocation « timmurphy.

NET concepts: Stack, heap, value types, reference types, boxing, and unboxing - CodeProject but be aware it may contain some inaccuracies. Snowcrash Snowcrash 70k 67 67 gold badges silver badges bronze badges.

This is incorrect. It is a very important distinction. See [link] stackoverflow. I did not say they were static variables. I said that int and cls1 are static items. Their memory is statically allocated and therefore they go on the stack. This is in contrast to an object which requires dynamic memory allocation which therefore goes on the heap.

I quote "Static items This is just flat out wrong. Static items go in the data segment, automatic items go on the stack. Also whoever wrote that codeproject article doesn't know what he is talking about. For instance, he says "primitive ones needs static type memory" which is completely untrue. That is just one of several inaccuracies. I edited your post because you have made serious technical mistakes about what goes in the stack and heap.

Show 6 more comments. Tom Leys Tom Leys A recommendation to avoid using the heap is pretty strong. Modern systems have good heap managers, and modern dynamic languages use the heap extensively without the programmer really worrying about it. I'd say use the heap, but with a manual allocator, don't forget to free! If you can use the stack or the heap, use the stack. If you can't use the stack, really no choice.

I use both a lot, and of course using std::vector or similar hits the heap. For a novice, you avoid the heap because the stack is simply so easy!! If your language doesn't implement garbage collection, Smart pointers Seporately allocated objects that wrap around a pointer which do reference counting for dynamically allocated chunks of memory are closely related to garbage collection and are a decent way of managing the heap in a safe and leak free manner.

They are implemented in various frameworks, but are also not that tough to implement for your own programs as well. Good point JonnoHampson - While you make a valid point, I'd argue that if you're working in a "high level language" with a GC you probably don't care about memory allocation mechanisms at all - and so don't even care what the stack and heap are.

Add a comment. The stack is managed for us. Important to note - this one static variable is shared among all instances of Dog, hence it is not dynamic! PetAnimal fido. PetAnimal rinTinTin. PetAnimal Dog. PetAnimal Output is: Thank you for petting me. But it's My favorite food is tuna Thank you for petting me. My favorite food is steak Thank you for petting me. My favorite food is milkbones Thank you for petting me. My favorite food is milkbones. I would refer to a static variable declared within a function as having only local accessibility , but would generally not use the term "scope" with it.

Some languages like PostScript have multiple stacks, but have a "heap" that behaves more like a stack. I defined scope as "what parts of the code can access a variable" and feel this is the most standard definition so I think we agree : — davec.

ZaeemSattar Think of the static function variable like a hidden global or like a private static member variable. Show 4 more comments. Others have answered the broad strokes pretty well, so I'll throw in a few details.

Peter Mortensen 29k 21 21 gold badges 97 97 silver badges bronze badges. Don Neufeld Don Neufeld Re "as opposed to alloc": Do you mean "as opposed to malloc"? How portable is alloca? EthanP 1, 2 2 gold badges 19 19 silver badges 26 26 bronze badges. What is a stack? A stack is a pile of objects, typically one that is neatly arranged. What is a heap? A heap is an untidy collection of things piled up haphazardly. Both together In a multi-threaded application, each thread will have its own stack.

Which is faster — the stack or the heap? And why? Java Memory Model The stack is the area of memory where local variables including method parameters are stored.

Community Bot 1 1 1 silver badge. Shreyos Adikari Shreyos Adikari This behavior is often customizable Because you've allocated the stack before launching the program, you never need to malloc before you can use the stack, so that's a slight advantage there. Daniel Papasian Daniel Papasian Also worth mentioning here that intel heavily optimizes stack accesses, especially things such as predicting where you return from a function.

I think many other people have given you mostly correct answers on this matter. Heath Heath. Another nitpick- most of the answers lightly imply that the use of a "stack" is required by the C language.

This is a common misconception, though it is the by far dominate paradigm for implementing C99 6. In fact, the word "stack" does not even appear in the C99 language standard: open-std. Take a look at the accepted answer to this question.

It says that the free store most probably is the same as the heap , though not necessarily is. Peter Peter 1, 8 8 silver badges 4 4 bronze badges. For instance, does it work on Windows? Is it only for Unix-like operating systems? What I know is that they always are. Could you please elaborate more? Classic Fortran behavior is to not use a stack at all. Some languages support exotic things like pass-by-name, which is effectively a textual substitution.

From WikiAnwser. Stack When a function or a method calls another function which in turns calls another function, etc. Heap The heap is simply the memory used by programs to store variables. 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 over time 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.

In Short A stack is used for static memory allocation and a heap for dynamic memory allocation, both stored in the computer's RAM.

The Heap The heap is a region of your computer's memory that is not managed automatically for you, and is not as tightly managed by the CPU. Now come to your question's answers. Already given in top. Abrar Jahin Abrar Jahin I also create the image below to show how they may look like:. Alireza Alireza Yousha Aleayoub Yousha Aleayoub 3, 4 4 gold badges 44 44 silver badges 59 59 bronze badges. A couple of cents: I think, it will be good to draw memory graphical and more simple: Arrows - show where grow stack and heap, process stack size have limit, defined in OS, thread stack size limits by parameters in thread create API usually.

Maxim Akristiniy Maxim Akristiniy 2, 2 2 gold badges 14 14 silver badges 20 20 bronze badges. I have something to share, although the major points are already covered.

Stack Very fast access. Stored in RAM. Function calls are loaded here along with the local variables and function parameters passed. Space is freed automatically when program goes out of a scope. Stored in sequential memory. Heap Slow access comparatively to Stack. Dynamically created variables are stored here, which later requires freeing the allocated memory after use.

Stored wherever memory allocation is done, accessed by pointer always. Interesting note: Should the function calls had been stored in heap, it would had resulted in 2 messy points: Due to sequential storage in stack, execution is faster.

Storage in heap would have resulted in huge time consumption thus making the whole program execute slower. If functions were stored in heap messy storage pointed by pointer , there would have been no way to return to the caller address back which stack gives due to sequential storage in memory. Pang 8, gold badges 82 82 silver badges bronze badges. Since some answers went nitpicking, I'm going to contribute my mite.

So many answers and I don't think one of them got it right There are two heaps: public and private. They are all global to the program, but their contents can be private, public, or global. Without stack no microprocessor can work. What is OPP? Do you mean to say that malloc is a kernel call? When programmers talk about a stack, this is the thread execution stack of the runtime, e.

Some of them even more than 1 data memory. This is to optimize the cycle duration Instruction fetch, data fetch and execute of previous instruction all in one machine cycle , thus take advantage from what they call pipe-lining. Net job? Net Interview Questions Next : What is.

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