Updated April 4, 2023
Difference Between C++ Stack vs Heap
The following article provides an outline for C++ Stack vs Heap. Stack is the data structure which follows the LIFO (Last In First Out) strategy. It is managed by the CPU and stores all the local variables created by the function and stack them one above the other. Every new function variable, once declared, it is pushed into the stack memory. Once the function execution/call is done, all the function data and variables are freed up. Stack has access to the local variables only. One of the biggest advantages (being a programmer) of using the stack is that the CPU manages the memory at the time of allocation or de-allocation (freed) the memory.
Heap is a free-floating region of the memory which is not totally managed by the CPU, but the programmer has to manage it. It allows the dynamic memory allocation, which is allocated at the time of execution of instructions using the malloc() and calloc() methods. Memory is allocated in the random order, and the pointers are used in order to access the data. All the global variables are by default stored in the heap memory. A programmer has to free the memory when using the heap once the task is performed using the free() method.
Head to Head Comparison Between C++ Stack vs Heap (Infographics)
Below are the top 8 differences between C++ Stack vs Heap:
Key Difference Between C++ Stack vs Heap
Let us discuss some of the major key differences between C++ Stack vs Heap:
- Stack is basically the region in the computer memory, which is automatically managed by the computer in order to store the local variables, methods and its data used by the function, whereas the heap is the free-floating region of memory which is neither automatically managed by the CPU nor by the programmer.
- Heap supports dynamic memory allocation with the use of malloc() and calloc() keywords. In order to release the memory, the programmer has to use the free() method, whereas in the case of Stack, memory allocated to store the variables and function data is released automatically by the compiler once the function execution ends.
- Stack is comparatively more flexible than heap as once the memory allocated for the stack cannot be changed, whereas, in the case of the heap, there is dynamic memory allocation so that the size can be altered.
- The main issue that can happen in the case of the stack is the memory shortage, whereas, in a heap, the main issue is fragmentation as the memory is allocated and released again and again.
- Implementing the stack is comparatively less costlier than the heap memory in C++.
- Once the stack memory falls outside of memory can lead to abnormal termination of the program, whereas in the case of the heap, being unable to free the memory in a heap can lead to memory leak issues as that memory will not get freed.
- Stack allows the stacking of local variables, method data and the sub-routines one above the other of the function or method, whereas heap does not stack the data but allocate the memory to each member using the dynamic memory allocation techniques.
- One of the biggest advantages of using the Stack memory is that there is no overhead of the memory management (allocation/ deallocation) on the programmer as the stack data is cleared every time after the function call is done, whereas, in the case of the heap, a programmer has to take the responsibility of the memory management and free the memory every time once the required task has been performed.
- Only local variables and method data can be accessed in the stack, whereas heap allows accessing global data and data present anywhere in the program.
- It is a bit slow and difficult in manipulating data in the heap memory as it allows the use of pointers in order to access the memory of the heap as the memory allocated is random, whereas stack allows the sequential access of data so it can be manipulated easily until the stack is out of memory.
- Heap is used when we need large memory variables to be used globally, and resizing is to be done frequently, whereas stack is used when the small variables need to be stored till the execution of function only and no/ very less resizing is to be done.
C++ Stack vs Heap Comparison Table
Let’s discuss the top comparison between C++ Stack vs Heap:
| S.No. | C++ Stack | Heap |
| 1. | In C++, stack memory is allocated in the contiguous blocks. | In the case of the heap, memory is allocated in the computer in random order. |
| 2. | In terms of accessing the data, a stack is comparatively faster than a heap. | Accessing data in heap memory is comparatively slower than a stack. |
| 3. | When it comes to a data structure, the stack follows the linear data structure. | Heap in C++ follows the hierarchical data structure. |
| 4. | In the case of stack memory, allocation and de-allocation of memory are done automatically by the compiler. | In the case of heap memory, allocation and deallocation of the memory need to be done by the programmer programmatically. |
| 5. | Memory used in the stack never gets fragmented as it is efficiently managed by OS at the time of allocation and deallocation. | Memory used in a heap gets fragmented as the blocks of memory first get allocated and then get freed up. |
| 6. | Stack allows the accessing of local variables only like function, method data, etc. | Data in a heap can also be accessed globally, unlike stack.
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| 7. | Variables in the stack memory cannot be resized as there is a restriction on the memory size. | In a heap, variables can be resized as there is no limit on the memory size. |
| 8. | Objects in stack memory are automatically destroyed after the function call is finished and the memory is deallocated. | The programmer needs to explicitly deallocate the memory of the variables in the case of the heap. |
Conclusion
The above description clearly explains what is stack and heap in C++ and what are the major differences between the two. However, both the stack and heap are used for the memory allocation in the programming but for different purposes. Both have their own advantages and disadvantages and can cause different issues; one needs to understand them deeply in order to use them according to the specific requirements of the programmer.
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