Computer Science
Dynamic Allocation of Array in C
Dynamic allocation of arrays in C refers to the process of allocating memory for an array during runtime rather than at compile time. This allows for more flexibility in the size of the array and can help conserve memory usage. The process involves using functions such as malloc() and free() to allocate and deallocate memory.
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7 Key excerpts on "Dynamic Allocation of Array in C"
eBook - PDFA Short Course in Computational Science and Engineering
C++, Java and Octave Numerical Programming with Free Software Tools
- David Yevick(Author)
- 2012(Publication Date)
- Cambridge University Press(Publisher)
This facilitates iterating over the characters in a string, as in string S = ''a string''; for ( char* p = S.begin( ); p != S.end( ); p++ ) cout << *p; which writes S to the terminal. 12.11 Static and dynamic memory allocation Static memory allocation. Memory for variables and arrays that are allocated when the compiler processes definitions is termed statically allocated. The com- piler also issues instructions to deallocate memory at the point at which a variable will no longer be used (generally when the block containing the definition is ter- minated). Thus in float a[10]; void fun( ) { int b[10]; } void main( ) { int c[10]; { int d[10]; } } the lifetime, or the period during which memory is reserved, of the global array a extends from the beginning to the end of the program while the lifetime of the local arrays b, c and d extends from their definition statements to the end of the encompassing block. Dynamic memory allocation. Despite the efficiency of compiler memory man- agement, the amount of memory required by a program often depends on the outcome of a user interaction or a logical condition evaluated during execu- tion. By postponing memory allocation until runtime, a program can exploit the resources of large computers while still executing successfully on small machines. For example, a computer game that reserves memory for a new player upon request should function on any system, but the maximum number of players will necessarily be limited by the available hardware. In C++ a running program can request memory from the operating system for a variable of a certain type by invoking the new operator. This operator returns 114 Pointers and dynamic memory the starting memory address of the dynamically allocated space as a temporary pointer with the type specified in the new statement.
eBook - ePubLearn C Programming
A beginner's guide to learning C programming the easy and disciplined way
- Jeff Szuhay(Author)
- 2020(Publication Date)
- Packt Publishing(Publisher)
Using Dynamic Memory AllocationNot all data can be allocated statically or automatically. Sometimes, the number of items to be manipulated is not known beforehand; that number can only be known at runtime and may vary from run to run, depending on external inputs (user input, files, and so on). In the preceding chapter, we examined automatic and static memory allocation. We now stand on the threshold of an incredibly powerful feature of C – dynamic memory allocation and manipulation. Once we pass this threshold, many flexible dynamic data manipulations will be available to us. We will briefly introduce many of these data structures and their uses in this chapter.As mentioned in the preceding chapter, dynamic memory is unnamed, so it can only be manipulated via pointers. Furthermore, dynamic memory has a different lifetime than either automatic or static memory.The following topics will be covered in this chapter:- Acquiring an introductory understanding of the power and flexibility of dynamic memory allocation
- Learning how to allocate and release dynamic memory
- Implementing a simple linked list dynamic data structure
- Creating and using a dynamic function pointer
- Becoming aware of various special considerations when using dynamic memory
- Learning about some other important dynamic data structures
Technical requirements
As detailed in the Technical requirements section of Chapter 1 , Running Hello, World! , continue to use the tools you have chosen.The source code for this chapter can be found at https://github.com/PacktPublishing/Learn-C-Programming .Introducing dynamic memory
Do we always know exactly how many objects we will need to manipulate and allocate memory for in a program? The answer is a resounding No !Not every situation or program can be efficiently addressed using just automatic or static memory. The number of objects may vary widely over the runtime of the program and from one run to another of the same program. The number of objects may depend on inputs from the user (covered in Chapter 20 , Getting Input From the Command Line , and Chapter 21 , Exploring Formatted Input ), from one or more existing files (covered in Chapter 22 , Working with Files , and Chapter 23 , Using File Input and File Output
eBook - ePub- Jeff Szuhay(Author)
- 2022(Publication Date)
- Packt Publishing(Publisher)
Chapter 18 : Using Dynamic Memory AllocationNot all data can be allocated statically or automatically. Sometimes, the number of items to be manipulated is not known beforehand; that number can only be known at runtime and may vary from run to run, depending on external inputs (such as user input and files). In the preceding chapter, we examined automatic and static memory allocation. We now stand on the threshold of an incredibly powerful feature of C – dynamic memory allocation and manipulation. Once we pass this threshold, many flexible dynamic data manipulations will be available to us. We will briefly introduce many of these data structures and their uses in this chapter.As mentioned in the preceding chapter, dynamic memory is unnamed, so it can only be manipulated via pointers. Furthermore, dynamic memory has a different lifetime than either automatic or static memory.The following topics will be covered in this chapter:- Acquiring an introductory understanding of the power and flexibility of dynamic memory allocation
- Learning how to allocate and release dynamic memory
- Implementing a simple linked list dynamic data structure
- Creating and using a dynamic function pointer
- Becoming aware of various special considerations when using dynamic memory
- Learning about some other important dynamic data structures
Technical requirements
As detailed in the Technical requirements section of Chapter 1 , Running Hello World! , continue to use the tools you have chosen.The source code for this chapter can be found at https://github.com/PacktPublishing/Learn-C-Programming-Second-Edition/tree/main/Chapter18 .Introducing dynamic memory
Do we always know exactly how many objects we will need to manipulate and allocate memory for in a program? The answer is a resounding no !Not every situation or program can be efficiently addressed using just automatic or static memory. The number of objects may vary widely over the runtime of the program and from one run to another of the same program. The number of objects may depend on inputs from the user (covered in Chapter 20 , Getting Input from the Command Line , and Chapter 21 , Exploring Formatted Input ), from one or more existing files (covered in Chapter 22 Working with Files
eBook - PDF- Roger T. Stevens(Author)
- 2014(Publication Date)
- Academic Press(Publisher)
This is really a little easier to understand than is the use of malloc. 237 Chapter 17 The Stack and the Heap Most C compilers divide the available memory into two areas, the stack and the heap. All variables that are defined in the main program and in the functions are assigned to memory space on the stack by the compiler. The compiler begins assigning space on the stack at the very bottom of the memory that is available for data and works upward. When the compiler is done, the stack assignments are complete and permanent. All remaining memory that is available for data is the heap. Space in the heap is assigned from the top down, by functions such as malloc and calloc. The heap is often called dynamic memory, since you can call it when you need it and then release it when you are through with it, whereas variables assigned to the stack have permanent memory assignments for the life of the program. It's nice to have some idea of how these memory assignment techniques work, but the compiler and program manipulations of the stack and heap will not directly affect your programming. The free Function The free function is used to release the memory assigned by malloc or calloc when you are finished using it. If you can release the memory occupied by one of your big arrays, when the operations on this array are done, then the memory will be available for another array that you may need later in the program. This is very important when you are using a lot of memory and spare memory is scarce. The function works like this. First you must have allocated memory by a statement like c = m a l l o c ( 3 2 0 0 0 ) ; or d = c a l l o c ( 1 5 6 7 0 , 2 ) ; To release this memory after you are through using it, you would write f r e e ( c ) ; f r e e ( d ) ; 238 Memory Management The farmalloc and farcalloc Functions While malloc and calloc are limited by the size of the memory model used, farmalloc and farcalloc can make use of all memory available to the computer.
No longer available |Learn moreHands-On System Programming with Linux
Explore Linux system programming interfaces, theory, and practice
- Kaiwan N Billimoria(Author)
- 2018(Publication Date)
- Packt Publishing(Publisher)
Dynamic Memory Allocation
In this chapter, we will delve into a key aspect of system programming on a modern OS—the management of dynamic (runtime) memory allocation and deallocation. We'll first cover the basic glibc APIs used to allocate and free memory dynamically. We'll then move beyond these basics, examining the program break within the VAS and the behavior of malloc(3) under differing circumstances.We will then immerse the reader in a few advanced discussions: demand-paging, memory locking and protection, and the usage of the alloca API. Code examples provide the reader with an opportunity to explore these topics in a hands-on manner. In this chapter, we will cover the following topics:- Basic glibc dynamic memory-management APIs and their correct usage in code
- The program break (and its management via the sbrk(3) API)
- The internal behavior of malloc(3) when allocating differing amounts of memory
- Advanced features:
- The demand-paging concept
- Memory locking
- Memory region protection
- Using the alloca (3) API alternative
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The glibc malloc(3) API family
In Chapter 2 , Virtual Memory , we learned that there are regions or segments meant for the use of dynamic memory-allocationwithin the process of Virtual Address Space (VAS ). The heap segment is one such dynamic region—a free gift of memory made available to the process for its runtime consumption.How exactly does the developer exploit this gift of memory? Not just that, the developer has to be extremely careful with matching memory allocations to subsequent memory frees , otherwise the system isn't going to like it!The GNU C library (glibc ) provides a small but powerful set of APIs to enable the developer to manage dynamic memory; the details of their usage is the content of this section.As you will come to see, the memory-management APIs are literally a handful: malloc(3)
eBook - PDF- Arvind Kumar Bansal(Author)
- 2013(Publication Date)
- Chapman and Hall/CRC(Publisher)
215 C H A P T E R 6 Dynamic Memory Management BACKGROUND CONCEPTS Abstract concepts in computation (Section 2.4); Abstract implementation (Chapter 5); Data abstraction (Section 4.1); Data structures concepts (Section 2.3); Principle of locality (Section 2.4.8). Memory reuse is an important requirement for executing large-scale programs. Different program subunits and dynamically created objects have a lifetime. Allocated memory gets released when the corresponding program units have finished execution, or when the recursive data structures or the dynamic data object are manually released by a programmer action. The memory is allocated in the control stack or the heap . The memory from the control stack is released when the frame of the called procedure is discarded, and the memory location can be reused for allocating another frame. Heap is a common area used mainly for recursive data structures and dynamically created data objects as in object-oriented programming languages such as C ++ , Java, and C#. The data structures allocated in heap are extended dynamically based upon run-time programmer request, and outlive the procedures in which they were created. Heap is visible throughout the life of a program. The allocated memory in heap is recycled only after the data entity has been released. Dynamic memory management is concerned about allocation, deallocation, and recy-cling of memory locations needed for data structures allocated in heap at runtime. If the objects are extended piecemeal, then it is difficult to access them in the frame of a pro-cedure, as different allocations need to be chained and accessed sequentially, while data objects in a frame are accessed using index and offsets. The data structures and objects that are constructed once and deleted before the lifetime of the subprogram that created them can be allocated in the control stack for efficient access and better memory reclaim.
eBook - PDF- Ivor Horton(Author)
- 2014(Publication Date)
- Wrox(Publisher)
Any program that processes a number of data items that is not known in advance can take advantage of the ability to allocate memory at run time. For example, in a program that stores information about the students in a class, the number of students is not fixed and their names will vary in length, so to deal with the data most efficiently, you’ll want to allocate space at execution time. Obviously, because dynamically allocated variables can’t have been defined at compile time, they can’t be named in your code. When they are created, they are identified by their address, which you store in a pointer. With the power of pointers, and the dynamic memory management tools in Visual C++, writing your programs to have this kind of flexibility is quick and easy. The Free Store, Alias the Heap In most instances, when your program is executed, there is unused memory in your computer. This unused memory is called the heap , or the free store . You can allocate space within the free store for a new variable of a given type using a special operator that returns the address of the space allo-cated. This operator is new , and it’s complemented by the operator delete , which releases memory previously allocated by new . You can allocate space in the free store for variables in one part of a program, and then release the space and return it to the free store after you have finished with it. This makes the memory available 164 ❘ CHAPTER 4 ARRAYS, STRINGS, AND POINTERS for reuse by other dynamically allocated variables. This is a powerful technique; it enables you to use memory very efficiently and in many cases results in programs that can handle much larger problems, involving considerably more data than otherwise might be possible. The new and delete Operators Suppose that you need space for a double variable. You can define a pointer to type double and then request that the memory be allocated at execution time.
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