To understand C++ memory management, let us explore its memory allocation mechanisms and the role of smart pointers in manual memory management for writing a robust C++ program.
C++ has manual memory management but does not support automatic garbage collection. Memory management is essential for a computer. Memory management optimizes the usage of main memory by allocating and deallocating memory for operating systems. It is to ensure memory is being used efficiently. Memory optimization can be achieved through Garbage Collection.
The term garbage collection refers to the process of automatic memory management. To be detailed, the unused memory during runtime will be reclaimed by the garbage collector by destroying the unreferenced objects. The definition of garbage collection is the automated process of deleting code that’s no longer referenced or used. This process automatically frees up memory space and makes it ideal for coding.
C++ is a middle-level programming language that is the same as CPP(C Plus Plus). Its first version was released in 1985. The C++ programming language was developed based on the C language. The C language was developed between 1969 and 1973, with the first edition of ‘The C Programming Language’ book published in 1978. The literal meaning of C plus is additional features are added to the C language.
C++ is an object-oriented programming language developed by Bjarne Stroustrup. Some of the features of this language are it is a machine-dependent, compiler-based, case-sensitive language. C++ also supports multi-threading and dynamic memory allocation. C++ also supports abstract data types that can be created using classes.
1. Manual Memory Management in C++
In Computer Science, manual memory management refers to the process in which the programmer manually identifies the unused objects and free() them by using predefined methods like free() in C. When writing a C++ program, memory is divided into two types: Heap memory and Stack memory.
1.1. Heap Memory
In heap memory of C++, heap allocations and deallocation of memory are done by the programmer explicitly by using the keywords new and delete, respectively, preceding the name of the constructor you want to manage memory. Two major drawbacks of heap memory are Memory leaks and Dangling pointers. If the programmer does not deallocate the memory, there may be memory leaks.
Dangling pointers refer to a pointer that is pointing to a process that is not in our operating system or pointing to a process that has already been deleted; such pointers are called Dangling pointers. It is not safe to use dangling pointers because they lead to memory faults.
1.2. Stack Memory
Whereas the Stack memory is managed automatically, i.e., after the execution, the memory will be deallocated automatically; hence, stack memory is also known as temporary memory. Every time we create an object while writing a program in C++, memory for the object will be created in the heap memory, and the information related to an object, like methods and variables, will be stored in stack memory.
The storage space for Stack memory is less compared to that of Heap memory because the deallocation of memory occurs automatically and much faster than the heap memory. Stack memory is considered to be much safer than heap memory because stack memory is only accessible to the parent process, but Heap memory is globally accessible in the program.
2. Smart Pointers in C++
Smart pointers are introduced in C++ to avoid a memory leak in Heap memory. A pointer whose lifetime is controlled by an encapsulating object is called a smart pointer. It is derived from the concept of raw pointers, where the lifetime of a pointer is not controlled by an encapsulating object. A raw pointer can also contain the address of another non-pointer variable. Smart pointers replace raw pointers to avoid memory leaks. There are three types of smart pointers: shared, unique, and weak pointers.
2.1. Shared Pointers
The first type of smart pointer is called a shared pointer, in which multiple pointers refer to one single object. Shared pointer uses a term called reference counting. Reference counting is used to count the number of pointers referring to an object. It is a simple Garbage collection algorithm. If the Reference counting algorithm searches for the objects with Zero Reference counting, those objects will be deleted by the garbage collector. However, there are certain limitations to reference counting, namely cycles. The syntax of the Shared pointer is given as std::shared_ptr, followed by the data type of the object that is being pointed and the name of the pointer.
2.2. Unique Pointer
The second type of smart pointer is called a Unique pointer. A unique pointer is introduced to overcome another limitation of Heap memory, i.e., memory leaks. A unique pointer is used to store a raw pointer, and when the raw pointer is no longer in use, the pointer is deallocated. It is also not possible to copy the raw pointer, which is being held by the unique pointer. This means that the unique pointer prevents the object present in a raw pointer from having more than one pointer. A unique pointer is used when we want a particular object to have a single ownership. The keyword used for a unique pointer is std::unique_ptr.
2.3. Weak Pointers
The third type of smart pointer is called a Weak pointer. A weak pointer contains a weak(non-owning) reference to an object that is held by a shared pointer. It must be converted into a shared pointer to access the object. Another use of a weak pointer is to overcome the limitations caused by reference counting. It is used to break the reference cycles formed due to reference counting. The keyword used for weak pointers is std::weak_ptr.
3. Garbage Collectors
Garbage Collection is a memory recovery feature that is built in many programming languages. A GC must contain one or more garbage collectors that free up the object space occupied by the unreferenced objects. A simple garbage collector must automatically free memory occupied by unreferenced objects. A garbage collector runs periodically from time to time, and GC frees the object’s space.
There are several types of garbage collection, and two of them are traditional garbage collection and real-time garbage collection. Traditional garbage collection may have arbitrarily long pauses in which the running program is interrupted by the garbage collector. At the same time, real-time garbage collection can collect unused memory with a fixed, short bound on the amount of time. Another type is generational garbage collection. In this type, the objects are divided into different generations based on time intervals.
4. Does C++ have a Garbage Collection?
Garbage collection is an automatic memory management system that is used in different programming languages. However, the C++ programming language did not have a garbage collection mechanism when it was first created. Generally, there are two types of garbage collection: implicit and explicit. Implicit garbage collection is a fully automated process that is not available in C++. Many other programming languages have automated garbage collection, such as C#, JAVA, Python, and others.
Another type of garbage collection mechanism is explicit garbage collection, which was initially not available in C++ but later introduced with the help of smart pointers. In explicit garbage collection, the programmer will explicitly free the unused objects. There is a lot of debate going on about whether to add an automated garbage collector to C++ or not. Because it decreases the performance of C++, some of them want to reduce the complexity by introducing the automated garbage collector. Smart pointers have also been introduced to reduce the complexity of garbage collection. Some of the garbage collection algorithms are reference counting, marking, sweeping, and copying.
5. Resource Management Techniques
Here, the resource we are discussing is Memory space. For a computer system, the storage, processes, and threads are limited. We need to follow certain protocols for efficient memory management. If we don’t follow those protocols, we may run out of memory because of a memory leak. We may also face issues like data race and data locks. Some features of C++ help in efficient memory management. Some of the rules for resource management are
- Manage resource handles automatically using resource handles and RAII
- Use raw pointers to denote individual objects in the interface
- A raw pointer is non-owning
- A raw reference is non-non-owning
- Scoped objects should be preferred; unnecessary heap allocation should be avoided
- Avoid using non-constant global variables
5.1. RAII(Resource Acquisition Is Initialization)
Resource Acquisition Initialization, or RAII, is a C++ programming technique. RAII programming technique helps in binding the life cycle of a resource that must be acquired before use to the lifetime of an object.RAII ensures that the resource is available to any function accessing the object. It ensures that the object is deleted after that object’s lifetime. Some of the features of RAII are
- This technique encapsulates each resource into a class.
- This technique always uses the resource through an instance of an RAII class.
The classes in the C++ library that manage their resources are a part of RAII. These classes acquire the resources in constructors and release them in their destructors implicitly. They don’t need to be explicitly freed.
6. Manual Memory Management in C++ and Garbage Collection- Pro’s
In different programming languages, there are two different approaches to memory management: garbage collection and manual memory management. Now, let us compare the manual memory management of C++ language with the garbage collection of other high-level languages.
6.1. Advantages of Garbage Collection
In garbage collection memory management is automated because it includes tracing garbage collection and helps in relieving the programmers from the responsibility of manually managing memory space. There are many garbage-collected languages. There is a higher risk of a memory leak when we are manually deleting the objects.
Garbage collectors also reduce the risk of memory leaks since the deallocation occurs automatically. For manual memory management, programmers must write complex code to allocate and deallocate the allocated memory. In garbage collection, we can reduce the code complexity and the chances of getting errors. Since the programmers don’t need to focus on memory management, they can increase their productivity by focusing on application-based code.
6.2. Advantages of Manual Memory Management in C++
C++ provides manual memory management through features like smart pointers, new and delete operators and RAII techniques. These features help the programmers to manually manage memory allocation and manually delete objects compared to garbage collection. Manual memory management also helps programmers better understand how memory is allocated and deallocated, which can be crucial when developing a real-time project with memory constraints.
During automatic garbage collection, garbage collectors take up system resources, which introduces latency in the application. However, in manual memory management, we can avoid this overhead problem. In C++, we can explicitly free the memory where they are no longer needed, and timely resource management is an important factor. Some external libraries and APIs may not be compatible with the garbage collectors, so it is better to manage memory manually.
7. Efficient Memory Management in C++
Efficient memory management is crucial for a programmer to write reliable and optimized code or for a developer to produce an efficient product. Especially when we’re working on projects that have limited resources, here are some of the tips for better memory management:
- Using Resource acquisition is initialization. RAII is a C++ algorithm in which a resource’s lifetime is linked with an object’s lifetime, so when an object that is no longer needed is deallocated, the memory space will also be deallocated. This technique ensures that the resources are released when they are no longer used, reducing the chance of memory leaks. We use smart pointers and classes to implement RAII for dynamic memory management.
- Whenever possible, avoid using manual memory management with new, deleted operators and raw pointers. Instead, if feasible, use smart pointers and predefined C++ standard libraries.
- Always ensure that the allocated memory is deallocated properly every time. Check for proper cleanup in the destructors or use smart pointers to automate memory management.
- Whenever possible, prefer stack memory over heap memory. Since the lifetime of stack memory is less than that of heap memory, the memory will be deallocated.
- Use the standard containers and algorithms like std::vector, std:: map, and std::set to provide well-tested functionality. Utilize the algorithms for C++ standard libraries to manipulate the data in the containers.
- In our code, we should clearly define the ownership and responsibilities for managing memory. When multiple objects need access to the same memory, we can use smart pointers.
- Online memory profiling tools or tools provided by the IDE can also be utilized to detect buffer overflows and other memory-related issues related to our code.
Efficient memory management is crucial for writing robust code. By following the above practices, we can reduce memory-related bugs.
8. Tools for Memory Debugging and Profiling
Memory debugging and profiling are important aspects of debugging, as a software developer needs to write an efficient and robust program. Some of the popular tools used for memory debugging are
- Valgrind: It is one of the most popular and widely used open-source tools for memory debugging and memory leak detection.
- GDB(GNU debugger): GDB is the most powerful tool for debugging many programming languages. Primarily it is used for debugging, but it is also used to analyze memory-related issues.
- AddressSanitizer: It is a runtime memory error detector built into GCC and Clang compilers. It helps in detecting various memory-related errors.
- MemorySanitizer(MSan): MemorySanitizer is another run-time memory error detector that is available in the Clang compiler. It is used to detect uninitialized memory reads.
- LeakSanitizer: LeakSanitizer is also a part of Clang’s compiler that detects memory leaks in C++ programs.
- Dynamic Analysis Tools: Several commercial and open-source dynamic tools, such as Intel Inspector and IBM Purify, have advanced memory debugging and profiling capabilities.
- Massif: Massif is a memory profiler provided by Valgrind. It helps us understand the memory usage patterns in C++ programs, including heap memory usage.
- Cpp check: Cpp check is a static code analysis tool for C++. It does not provide runtime debugging or profiling but can identify memory issues in code by analyzing source code.
- Electric Fence: Electric Fence is a simple memory debugging library that can help detect buffer overflows. It is less powerful than some other tools but can be useful for quick checks. The choice of tools depends on the specific needs, the type of platform we are working on, and operating systems like Windows, Linux, Mac, and other OS.
Key Note
Memory utilization is a critical aspect of software development, ensuring efficient utilization of system resources while minimizing the risk of memory-related issues. C++ is a middle-level programming language, which offers the programmer a wide range of tools and techniques for managing memory effectively.
One of the key distinctions in C++ memory management is the division between stack and heap memory. Stack memory is automatically managed, making it safer and faster, while heap memory requires manual allocation and deallocation, posing the risk of memory leaks and dangling pointers. To address these challenges, C++ introduced smart pointers, offering safer and more reliable memory utilization options.
Garbage collection, an automatic cleanup system found in other high-level languages like C#, Java, and Python, was not originally part of C++. However, there have been discussions about introducing automated collection to C++ to reduce complexity and the risk of memory leaks. Still, some argue for manual memory management’s advantages, as it provides developers with greater control, which is vital for real-time projects and compatibility with certain libraries and APIs.
Efficient memory utilization in languages like C++ can be achieved by adhering to best practices, such as using Resource Acquisition Is Initialisation(RAII), preferring smart pointers over raw pointers, ensuring proper memory deallocation, favoring stack memory when possible, and utilizing standard containers and algorithms. Additionally, the use of memory profiling tools like Valgrind, GDB, and others can help identify and rectify memory-related issues in code.
In essence, effective memory use in languages like C++ requires a balance between manual control and automation, as well as a commitment to following best practices and utilizing the right tools for debugging and profiling. By implementing these strategies, developers can write more robust and reliable code, minimizing memory-related bugs and ensuring efficient resource utilization in their software projects.
Last Updated on by Arnab