pointer and array in c++ pdf

Pointer And Array In C++ Pdf

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An array is a data structure that stores an element of the same data type sequentially. You can see an array as a collection of variables of a similar data type. Instead of declaring each variable and assigning it a value individually, you can declare one variable the array and add the values of the various variables to it.

Pointer (computer programming)

Donald Knuth , Structured Programming, with go to Statements [1]. In computer science , a pointer is an object in many programming languages that stores a memory address.

This can be that of another value located in computer memory , or in some cases, that of memory-mapped computer hardware.

A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture. Using pointers significantly improves performance for repetitive operations, like traversing iterable data structures e.

In particular, it is often much cheaper in time and space to copy and dereference pointers than it is to copy and access the data to which the pointers point. Pointers are also used to hold the addresses of entry points for called subroutines in procedural programming and for run-time linking to dynamic link libraries DLLs.

In object-oriented programming , pointers to functions are used for binding methods , often using virtual method tables. A pointer is a simple, more concrete implementation of the more abstract reference data type.

Several languages, especially low-level languages , support some type of pointer, although some have more restrictions on their use than others. While "pointer" has been used to refer to references in general, it more properly applies to data structures whose interface explicitly allows the pointer to be manipulated arithmetically via pointer arithmetic as a memory address, as opposed to a magic cookie or capability which does not allow such.

Primitive pointers are often stored in a format similar to an integer ; however, attempting to dereference or "look up" such a pointer whose value is not a valid memory address will cause a program to crash. To alleviate this potential problem, as a matter of type safety , pointers are considered a separate type parameterized by the type of data they point to, even if the underlying representation is an integer.

In , Soviet computer scientist Kateryna Yushchenko invented the Address programming language that made possible indirect addressing and addresses of the highest rank — analogous to pointers. This language was widely used on the Soviet Union computers.

However, it was unknown outside the Soviet Union and usually Harold Lawson is credited with the invention, in , of the pointer. According to the Oxford English Dictionary , the word pointer first appeared in print as a stack pointer in a technical memorandum by the System Development Corporation.

In computer science , a pointer is a kind of reference. A data primitive or just primitive is any datum that can be read from or written to computer memory using one memory access for instance, both a byte and a word are primitives.

A data aggregate or just aggregate is a group of primitives that are logically contiguous in memory and that are viewed collectively as one datum for instance, an aggregate could be 3 logically contiguous bytes, the values of which represent the 3 coordinates of a point in space. When an aggregate is entirely composed of the same type of primitive, the aggregate may be called an array ; in a sense, a multi-byte word primitive is an array of bytes, and some programs use words in this way.

In the context of these definitions, a byte is the smallest primitive; each memory address specifies a different byte. The memory address of the initial byte of a datum is considered the memory address or base memory address of the entire datum. A memory pointer or just pointer is a primitive, the value of which is intended to be used as a memory address; it is said that a pointer points to a memory address.

It is also said that a pointer points to a datum [in memory] when the pointer's value is the datum's memory address. More generally, a pointer is a kind of reference , and it is said that a pointer references a datum stored somewhere in memory ; to obtain that datum is to dereference the pointer. The feature that separates pointers from other kinds of reference is that a pointer's value is meant to be interpreted as a memory address, which is a rather low-level concept.

References serve as a level of indirection: A pointer's value determines which memory address that is, which datum is to be used in a calculation. Because indirection is a fundamental aspect of algorithms, pointers are often expressed as a fundamental data type in programming languages ; in statically or strongly typed programming languages, the type of a pointer determines the type of the datum to which the pointer points.

When setting up data structures like lists , queues and trees, it is necessary to have pointers to help manage how the structure is implemented and controlled. Typical examples of pointers are start pointers, end pointers, and stack pointers. These pointers can either be absolute the actual physical address or a virtual address in virtual memory or relative an offset from an absolute start address "base" that typically uses fewer bits than a full address, but will usually require one additional arithmetic operation to resolve.

Relative addresses are a form of manual memory segmentation , and share many of its advantages and disadvantages. A two-byte offset, containing a bit, unsigned integer, can be used to provide relative addressing for up to 64 KiB 2 16 bytes of a data structure. This can easily be extended to , or KiB if the address pointed to is forced to be aligned on a half-word, word or double-word boundary but, requiring an additional "shift left" bitwise operation —by 1, 2 or 3 bits—in order to adjust the offset by a factor of 2, 4 or 8, before its addition to the base address.

Generally, though, such schemes are a lot of trouble, and for convenience to the programmer absolute addresses and underlying that, a flat address space is preferred. X'29' can be used to point to an alternative integer value or index in an array e.

In this way, characters can be very efficiently translated from ' raw data ' to a usable sequential index and then to an absolute address without a lookup table. Control tables that are used to control program flow usually make extensive use of pointers.

The pointers, usually embedded in a table entry, may, for instance, be used to hold the entry points to subroutines to be executed, based on certain conditions defined in the same table entry. The pointers can however be simply indexes to other separate, but associated, tables comprising an array of the actual addresses or the addresses themselves depending upon the programming language constructs available. They can also be used to point to earlier table entries as in loop processing or forward to skip some table entries as in a switch or "early" exit from a loop.

For this latter purpose, the "pointer" may simply be the table entry number itself and can be transformed into an actual address by simple arithmetic. Pointers are a very thin abstraction on top of the addressing capabilities provided by most modern architectures. In the simplest scheme, an address , or a numeric index , is assigned to each unit of memory in the system, where the unit is typically either a byte or a word — depending on whether the architecture is byte-addressable or word-addressable — effectively transforming all of memory into a very large array.

The system would then also provide an operation to retrieve the value stored in the memory unit at a given address usually utilizing the machine's general purpose registers. In the usual case, a pointer is large enough to hold more addresses than there are units of memory in the system. This introduces the possibility that a program may attempt to access an address which corresponds to no unit of memory, either because not enough memory is installed i. The first case may, in certain platforms such as the Intel x86 architecture, be called a segmentation fault segfault.

The second case is possible in the current implementation of AMD64 , where pointers are 64 bit long and addresses only extend to 48 bits. Pointers must conform to certain rules canonical addresses , so if a non-canonical pointer is dereferenced, the processor raises a general protection fault.

On the other hand, some systems have more units of memory than there are addresses. In this case, a more complex scheme such as memory segmentation or paging is employed to use different parts of the memory at different times.

The last incarnations of the x86 architecture support up to 36 bits of physical memory addresses, which were mapped to the bit linear address space through the PAE paging mechanism. Another example in the same computer family was the bit protected mode of the processor, which, though supporting only 16 MB of physical memory, could access up to 1 GB of virtual memory, but the combination of bit address and segment registers made accessing more than 64 KB in one data structure cumbersome.

There are analogous concepts such as file offsets, array indices, and remote object references that serve some of the same purposes as addresses for other types of objects. They are primarily used for constructing references , which in turn are fundamental to constructing nearly all data structures , as well as in passing data between different parts of a program.

In functional programming languages that rely heavily on lists, data references are managed abstractly by using primitive constructs like cons and the corresponding elements car and cdr , which can be thought of as specialised pointers to the first and second components of a cons-cell. This gives rise to some of the idiomatic "flavour" of functional programming. By structuring data in such cons-lists , these languages facilitate recursive means for building and processing data—for example, by recursively accessing the head and tail elements of lists of lists; e.

By contrast, memory management based on pointer dereferencing in some approximation of an array of memory addresses facilitates treating variables as slots into which data can be assigned imperatively. When dealing with arrays, the critical lookup operation typically involves a stage called address calculation which involves constructing a pointer to the desired data element in the array.

In other data structures, such as linked lists , pointers are used as references to explicitly tie one piece of the structure to another. Pointers are used to pass parameters by reference. This is useful if the programmer wants a function's modifications to a parameter to be visible to the function's caller. This is also useful for returning multiple values from a function. Pointers can also be used to allocate and deallocate dynamic variables and arrays in memory.

Since a variable will often become redundant after it has served its purpose, it is a waste of memory to keep it, and therefore it is good practice to deallocate it using the original pointer reference when it is no longer needed.

Failure to do so may result in a memory leak where available free memory gradually, or in severe cases rapidly, diminishes because of an accumulation of numerous redundant memory blocks. The basic syntax to define a pointer is: [4]. Because the C language does not specify an implicit initialization for objects of automatic storage duration, [5] care should often be taken to ensure that the address to which ptr points is valid; this is why it is sometimes suggested that a pointer be explicitly initialized to the null pointer value, which is traditionally specified in C with the standardized macro NULL : [6].

Dereferencing a null pointer in C produces undefined behavior , [7] which could be catastrophic. However, most implementations [ citation needed ] simply halt execution of the program in question, usually with a segmentation fault. In any case, once a pointer has been declared, the next logical step is for it to point at something:. This assigns the value of the address of a to ptr. For example, if a is stored at memory location of 0x then the value of ptr will be 0x after the assignment.

To dereference the pointer, an asterisk is used again:. This means take the contents of ptr which is 0x , "locate" that address in memory and set its value to 8. If a is later accessed again, its new value will be 8. This example may be clearer if memory is examined directly. Assume that a is located at address 0x in memory and ptr at 0x; also assume this is a bit machine such that an int is bits wide. The following is what would be in memory after the following code snippet is executed:.

The NULL pointer shown here is 0x By assigning the address of a to ptr :. Clearly, accessing a will yield the value of 8 because the previous instruction modified the contents of a by way of the pointer ptr. For example, an array array can be declared and used in the following manner:. This allocates a block of five integers and names the block array , which acts as a pointer to the block.

Another common use of pointers is to point to dynamically allocated memory from malloc which returns a consecutive block of memory of no less than the requested size that can be used as an array. While most operators on arrays and pointers are equivalent, the result of the sizeof operator differs.

If array is located in memory starting at address 0x on a bit little-endian machine then memory will contain the following values are in hexadecimal , like the addresses :. Represented here are five integers: 2, 4, 3, 1, and 5. These five integers occupy 32 bits 4 bytes each with the least-significant byte stored first this is a little-endian CPU architecture and are stored consecutively starting at address 0x Below is an example definition of a linked list in C.

This pointer-recursive definition is essentially the same as the reference-recursive definition from the Haskell programming language :. Nil is the empty list, and Cons a Link a is a cons cell of type a with another link also of type a.

The definition with references, however, is type-checked and does not use potentially confusing signal values. For this reason, data structures in C are usually dealt with via wrapper functions , which are carefully checked for correctness.

Pointer (computer programming)

Just like we can declare an array of int , float or char etc, we can also declare an array of pointers, here is the syntax to do the same. Here arrop is an array of 5 integer pointers. It means that this array can hold the address of 5 integer variables. In other words, you can assign 5 pointer variables of type pointer to int to the elements of this array. Notice how we are assigning the addresses of a , b and c. In line 9, we are assigning the address of variable a to the 0th element of the of the array. Similarly, the address of b and c is assigned to 1st and 2nd element respectively.

C functions pass arguments “by value”. • To pass arguments “by reference,” use pointers void swap(int x, int y). { int t; t = x; x = y; y = t;. } int a = 3, b = 7; swap(a, b);.

C++ Pointers and Arrays

Pointer to an array :. Pointer to an array is also known as array pointer. We are using the pointer to access the components of the array.

In this tutorial, we will learn about the relation between arrays and pointers with the help of examples. Not only can a pointer store the address of a single variable, it can also store the address of cells of an array. Here, ptr is a pointer variable while arr is an int array.

Pointers give greatly possibilities to 'C' functions which we are limited to return one value. With pointer parameters, our functions now can process actual data rather than a copy of data. In order to modify the actual values of variables, the calling statement passes addresses to pointer parameters in a function. Here we will discuss the program process: We declare the function responsible for swapping the two variable values, which takes two integer pointers as parameters and returns any value when it is called.

World's No 1 Animated self learning Website with Informative tutorials explaining the code and the choices behind it all. Powered by Inplant Training in chennai Internship in chennai. In this article, you'll learn about the relation between arrays and pointers, and use them efficiently in your program. Pointers are the variables that hold address. Not only can pointers store address of a single variable, it can also store address of cells of an array.

Pointers are extremely powerful because they allows you to access addresses and manipulate their contents. But they are also extremely complex to handle. Using them correctly, they could greatly improve the efficiency and performance. On the other hand, using them incorrectly could lead to many problems, from un-readable and un-maintainable codes, to infamous bugs such as memory leaks and buffer overflow, which may expose your system to hacking. Many new languages such as Java and C remove pointer from their syntax to avoid the pitfalls of pointers, by providing automatic memory management.

Array of Pointers in C

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C++ Pointers and Arrays


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