A Brief Context About Pointers
To put it in simpler terms, a pointer is defined as a variable whose value is a memory address that contains another variable's value. Variables mostly render as data values but pointers, as previously mentioned, are a class of variables which point or store the address of a location where data is rendered in memory. With this feature programmers are able to do rather complex operations like constructing data structures or allocating memory dynamically.
For example, It's rather inefficient to send a big array to a function directly when you send the address of the array instead. The program is said to be efficient because not only is time saved but also memory is conserved. With pointers, the memory can be controlled in a more effective manner therefore optimizing performance due to having to deal with large sets of data.
Memory Management in C++
In C++, memory allocation takes place through two main types of memory which will be analyzed in-depth in this article: stack memory and heap memory.
1. Stack Memory:
The stack is the main repository for local variables. When a given function is designed to use local variables, the stack is expanded to make more room for those variables. Those local variables are allocated memory in the stack but that memory is freed as soon as the function exits. Local variables, however, are usually of small size and stack memory is constrained, so it is not useful for data that has been allocated dynamically.
2. Heap Memory:
Heap Memory, on the other hand, takes up the dynamically allocated memory. This occurs during the program’s runtime while using commands like `new` in C++. Memory allocated in heap does not get automatically freed after a particular function gets terminated as is the case in stack memory. It is only freed once deleted from memory through the command `delete` in C++. This provides the programmer access to more space but requires proper handling of memory in order to prevent memory leaks.
The Role of Pointers in Memory Management
C++ makes extensive use of pointers. Pointers assist with the allocation of memory which assists programs in creating and manipulating variables through the use of dynamic memory allocation. Heap memory that is allocated via pointers is not at any time automatically deallocated when a variable goes out of scope unlike stack allocated variables. This scenario explains why manual fixing of memory becomes relevant and is one of the key issues faced when filing coding tasks when coding in C++.
When a pointer is used to represent a dynamically allocated memory address, it is the programmer that needs to politely request that the memory is released when it is no longer required using the `delete` or `delete[]`. In the event that memory is not properly released this can potentially lead to memory leaks in which instance the memory that is no longer useful is still allocated taking up unnecessary resources.
Dynamic Memory Allocation
Memory allocation is the controlled process of requesting for memory placements and usually involves free areas on a physical device such as a computer and in this case within the context of the computer is called Dynamic Memory Allocation and is opposed to static allocation during compile. Variables of single types must use `new` when requesting dynamic memory allocation and `new[]` when dealing with arrays in C++. Dynamic memory allocation permits the program to ask for memory when it is needed to be allocated keeping in mind the fact that in some cases the user may not know the accurate amount of memory that will be needed.
By way of illustration, consider a program that requires an array of integers but does not know its size until the program is run. In such a case, the programmer will use `new[]` to request an array of a certain size. When the variable is no longer required, the programmer is obliged to free the memory by calling `delete[]`. If this is ignored, the memory is not released and a memory leak occurs.
Managing Memory with Pointers
In C++, pointers in conjunction with memory management entails a number of key responsibilities. First, a pointer must be assigned the value returned from `new` or `new[]` during the process of obtaining memory, and this value should not be omitted if memory was allocated. A pointer is set to the address returned from the allocated memory and can be used to obtain or adjust the values stored there.
When an object or array is no longer required, `delete` or `delete[]` must be used to free the memory. Upon failure to utilize `delete`, there would be problems of memory being left unused and which cannot be reclaimed by the system, leading to application performance problems and finally application crashing.
Another significant course of action is to prevent dangling pointers from occurring. A dangling pointer is said to exist when a pointer still points to a memory address that has been freed or allocated to some other process. Whenever dangling pointers are used, the resulting effects can be undefined. This may include crashing of the system or corruption of data. To avoid this from happening, a common practice that programmers undertake is to set such pointers to `nullptr` once they have been deleted.
Common Problems Related To Memory Management
Pointers and allocating dynamic memory comes with its own set of benefits and features, but alongside it introduces additional risks and makes people more prone to errors. One of the most common issues that tends to arise is memory leaks that occur when memory is never deleted, but is allocated. This can be the case when a programmer forgets to use `delete`, or when the program crashes before memory is freed. Memory leaks over a long time span can build up causing the application to use more and more memory till the device resources have been exhausted.
Accessing memory that has already been freed is another issue but not as common as the other ones. Also known as dangling pointers, it occurs when one tries to access memory which has been deallocated. Since a pointer is trying to point at a location which has already been deallocated, it results in undefined behavior whenever any operation is done on it. For this reason one must make it a habit to delete pointers after they have been used to prevent this problem from occurring.
Additionally, incorrect utilization of pointers may result in the dreaded phenomenon known as buffer overflows, which occurs when data is inscribed or written beyond a particular memory address. This is dangerous in the sense that it has the capacity to overwrite data locations next to it, which in the long run leads to data corruption or crashes or security risks.
Smart Pointers in Modern C++
As the language progressed, there was a feature that was introduced in C++ which was known as Smart Pointers which can be useful. A smart pointer is essentially an object that behaves like a classic pointer, but does all the memory management work for you. As the rest, smart pointers solve a lot of the issues connected to this manual memory management, and especially memory leaks and dangling pointers.
Types of smart pointers available include `std::unique_ptr`, `std::shared_ptr`, and `std::weak_ptr`. Each one has a different behavior to offer. As an example, this pointer `std::unique_ptr` makes certain that only one pointer at the time is in charge of an object and will physically remove the object once the pointer no longer exists. `std::shared_ptr` empowers pointer duplication by more than one group where an object is shared but once the last pointer goes off there will not be more objects to point to.
It is apparent that when it comes to managing memory, smart pointers eliminate a lot of the tasks that cut the chance of making errors making it easy to maintain programs.
