The stack is one of the data structures. This is for those who want to seriously work in IT in the future: one of the fundamental concepts that affect the quality of your code but does not apply to any particular programming language. In this article, we will discuss the peculiarities of stack technology.
What is a data stack?
Before writing a program, it is important to choose the right data structure that provides an effective solution to the problem. The same data can be stored in structures that require different amounts of memory, and the algorithms for working with each structure can have different efficiency. Data structures define objects that are organized in a certain way and the operations that can be performed on objects. Access to objects and all operations with them are carried out only through the interface. The interface decouples the implementation of the data structure from the client and is “opaque” to the client.
Container classes are designed to store data organized in a specific way. For each type of container, methods for working with its elements are defined, which do not depend on the specific type of data that is stored in the container. Therefore, the same kind of container can be used to store data of different types.
Containers can be divided into two types: sequential and associative. Consecutive containers provide storage of a finite number of similar items in a continuous sequence. Sequential containers include vectors, deque, list, and so-called adapters: stacks, queue, and priority queue. Each type of container provides its own set of actions on data and the choice of this or that container depends on what exactly needs to be done with the data in the program.
A stack is a data structure that is a specially organized list of items. Access to the elements of the stack is carried out according to the LIFO (Last In First Out) principle – the last to come, the first to come out. The operating principle of this data structure is similar to an automatic firearm magazine. The cartridges are placed in the magazine from top to bottom, and only the top cartridge is always used. A queue is a sequential container that adds items to the end of the queue and retrieves items from the front of the queue.
Let’s select typical operations on the stack and its elements:
- adding an item to the stack;
- removing an item from the stack;
- checking if the stack is empty;
- viewing the element at the top of the stack without deleting;
- clearing the stack.
Stack overflow
There are two kinds of stack in programming – the call stack and the data stack.
Almost always, the call stack is stored in RAM and has a certain size. If you have a lot of nested calls or recursion with a very large nesting depth, then the following situation may happen:
- recursion everything works and works;
- with each new iteration of the recursion, a new element is added to the stack;
- when there are too many elements, memory will run out, new elements will have nowhere to add and a stack overflow will occur.
Overflow is bad: data can get into someone else’s memory area and write itself instead of the previous data. This can cause other programs or the computer itself to malfunction. It is also possible to inject malicious code into RAM in this way: if the program does not work well with the stack, you can deliberately cause an overflow and write something malicious into memory.