A Null Pointer is a pointer that does not point to any memory location. It stores the base address of the segment. The null pointer stores the Null value while void is the type of the pointer.

A null pointer is a special reserved value that is defined in a stddef header file. Here, Null means that the pointer is referring to the 0th memory location.

If we do not have any address which is to be assigned to the pointer, then it is known as a null pointer. When a NULL value is assigned to the pointer, then it is considered as a Null pointer.

   Declare a pointer p of the integer datatype.

Let us see an example of how null pointers are created.

printf("The value of pointer assigned is : %x\n", ptr  );

Explanation: In the above code, we are initializing the variable “ptr”  to 0 (zero) so when we print the pointer value which Null pointer.

Suppose let us take another example where the pointer variables are not assigned to any memory address.

printf("Address of the given pointer variable: %d", pointer_var);

printf("Value of pointer variable is : %d", * pointer_var);

timeout: the monitored command dumped core

sh:  line 1:  15771 Segmentation fault         timeout 10s main

Explanation: In the above code, the pointer_var variable is not assigned to zero nor does it store any address of any variable in it, when the code is executed during the compile-time it gives an error where it throws garbage value which might harm your computer. So usually when we try to write or read from a null pointer we get a run time error as we saw in the above code which we get segmentation fault which is a null pointer exception sometimes it also throws an exception as a null pointer exception. In most of the examples, a null pointer is used to denote or indicate the end of the list.

To avoid this exception we can rewrite the above code as

printf("Value of pointer variable is : %d",* pointer_var);

Explanation: In the above-modified code, we assign a pointer_var to the “NULL” value and we check with the condition if the value of the pointer is null or not. In most the operating system, codes or programs are not allowed to access any memory which has its address as 0 because the memory with address zero 0is only reserved by the operating system as it has special importance, which states that the pointer is not intended to point to any memory location that can be accessible. So by default, we can say that if a pointer is assigned to zero then it is nothing but it only points to nothing.

A Null pointer is a pointer that is a variable with the value zero or an address leading to nothing in the C programming language. To make a variable a null pointer, we use the keyword NULL, which is a predefined macro in C. Also, after the data is no longer in use, the memory allocated to it must be released, or the dangling pointer would reappear. Also, never declare a pointer without first assigning NULL to it, as this will result in an error when the program is launched.

Let's discuss everything about the null pointer.

Everything  About Null Pointer 

A pointer is used to store the address of a variable in C. Pointer reduces the access time of a variable. However, In C, we can also define a pointer to store the address of another pointer. Such a pointer is known as a double pointer (pointer to pointer). The first pointer is used to store the address of a variable whereas the second pointer is used to store the address of the first pointer.

   Declare a pointer p1 of the integer datatype.

   Declare another double-pointer p2 of the integer datatype.

   Initialize p1 as the pointer to variable v.

   Initialize p2 as the pointer to variable p1.

   Print “Value of v using single pointer”.

   Print “Value of v using double pointer”.

      Print the value of double pointer p2.

In this article, we will see how to declare double-pointer with syntax and example, and also we will see how to use them in the C programming language. So let us start from the syntax.

In the above syntax, we can see the variable pointer_var is prefixed with two stars (**), also known as the indirection operator (*) for declaring the double-pointer.

So in general if the pointer is pointing to or referring to an object in memory then a double-pointer is a pointer that would be pointing to or referring to another point where it is pointing to an object in memory. Let us see how this exactly works by below example and pictorial form:

Let's see an example of a double-pointer.

     //This pointer pr2 is a double pointer

     /* Assigning the address of variable num to the

     /* Assigning the address of pointer pr2 to the

     /* Possible ways to find value of variable num*/

     printf("\n Value of num is: %d", num);

     printf("\n Value of num using pr2 is: %d", *pr2);

     printf("\n Value of num using pr1 is: %d", **pr1);

     /*Possible ways to find address of num*/

     printf("\n Address of num is: %p", &num);

     printf("\n Address of num using pr2 is: %p", pr2);

     printf("\n Address of num using pr1 is: %p", *pr1);

     printf("\n Value of Pointer pr2 is: %p", pr2);

     printf("\n Value of Pointer pr2 using pr1 is: %p", *pr1);

     printf("\n Address of Pointer pr2 is:%p",&pr2);

     printf("\n Address of Pointer pr2 using pr1 is:%p",pr1);

     /*Double pointer value and address*/

     printf("\n Value of Pointer pr1 is:%p",pr1);

     printf("\n Address of Pointer pr1 is:%p",&pr1);

Value of Pointer pr2 using pr1 is: XX771230

Address of Pointer pr2 using pr1 is: 66X123X1

There are some confusions regarding the output of this program, when you run this program you would see the address similar to this: 0x7fff54da7c58. The reason I have given the address in different format is because I want you to relate this program with the diagram above. I have used the exact address values in the above diagram so that it would be easy for you to relate the output of this program with the above diagram.

You can also understand the program logic with these simple equations:

In this article, we can conclude that pointers are also variables that can store values. But a pointer usually stores the value as the address of another variable. So commonly we can define double-pointer as pointer to pointer, which means a pointer stores the address of another pointer. In this way, double pointers are used in allocating the memory or assigning the value as the address of another pointer to access the value even outside the function call bypassing the reference to the argument using ** arg.

In this tutorial, we'll know what a double-pointer is and how it works.

What Is Double-Pointer In C? How Is It Work?

The void pointer in C is a pointer that is not associated with any data types. It points to some data location in the storage means points to the address of variables. It is also called a general-purpose pointer. In C, malloc() and calloc() functions return void * or generic pointers.

The Declaration of the void pointer is given below:

In the above declaration, the void is the type of the pointer, and 'ptr' is the name of the pointer.

      Print the value of a using pointer p.

      Print the value of b using pointer p

The pointer conception in C is veritably useful as it helps in memory allocation and address operation. It helps in enforcing two types of pointers videlicet void pointers and general pointers. Thus, it's occasionally called a general- purpose pointer. Representing and Dereferencing plays a vital part in pointer conception as well as in void pointer. 

Let’s walk through the working of the void pointer in C which is performed using pointers that aren't at each associated with any other data type. It contains any data type which will contain the address of the value. a pointer declared with keyword void is a void pointer in C. As mentioned before representing and dereferencing are some of the styles associated with pointer conception which will be used. Dereferencing comes into picture whenever it's a need to pierce the stored value in the pointer variable. Also, there's a type of casting value which is used for dereferencing because none of the pointer value is associated with the data types. The compiler also can not find the type of variable which is refocused by any type of void pointer. One point to keep in mind is void pointer won't support any kind of computation operation. It makes use of indirection driver‘*’to serve the entire purpose. But to serve this problem there's a need to typecast the pointer variable as well for dereferencing. The operation of typecasting is demanded because there's no presence of datatype associated at the time of protestation of the pointer. In short, the compiler does n’t have any applicable source to get an idea of the type of data type declared. So, it performs the typecasting and meets the demand to give an suggestion of the type of data type used by the void pointer at the time of protestation. 

Size of the void pointer is the coming point of focus as a void pointer in C functions nearly the same as character pointer in C which means a representation of Character type of pointer will be the same as a void pointer inC. Also, the size will vary according to the platform being used by the pointer. Memory allocation also works in some format which means void pointer has the beauty of furnishing an improvement point of memory operation with calloc () and malloc () functions which eventually returns the void as return type. Thus, these functions can be used to allocate the memory of any data type. 

The most important theme line of all the added advantage which pointer has is that it has the power of reusability for void pointers. It can store any type of object and can recoup any type of object from the defined object using the indirection driver and driver with proper typecasting. Dereferencing driver as part of the pointer can be used for easy access or manipulation of the stored data in the memory position for the pointer pointing the data type and it'll have a direct impact on the value of the data type. 

malloc() and calloc() return void * type and this allows these functions to be used to allocate memory of any data type (just because of void *)

// Note that malloc() returns void * which can be

    // typecasted to any type like int *, char *, ..

Note that the above program compiles in C, but doesn’t compile in C++. In C++, we must explicitly typecast return value of malloc to (int *).

1. void pointers cannot be dereferenced. For example the following program doesn’t compile.

Compiler Error: 'void*' is not a pointer-to-object type

The following program compiles and runs fine.

2. The C standard doesn’t allow pointer arithmetic with void pointers. However, in GNU C it is allowed by considering the size of void is 1. For example the following program compiles and runs fine in gcc.

void pointer in C is used to mitigate the problem of pointers pointing to each other with a different set of values and data types. There is also a reduction in explicit typecasting. Also, it supports the generic pointer type which makes it as a generic-purpose compiler.

In this blog, you'll learn about the void pointer of C.

C Void Pointer

Hibernate <Generator> instructions are used to generate the number one key or an identifier. More than one algorithm is used to generate the number one key. <generator> tag is a subtag of <id> tag. All the generator training put into effect hibernate.id.Identifier generator interfaces and overrides the generate(session implementor, item) method. In case you need to outline your consumer-described generator, you must put in force the identifier generator interface and override the generate().

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

Hibernate provides multiple algorithms such as :

assigned: It's far the default set of rules. If no <generator> tag is described then the assigned generator magnificence is used. On this algorithm, the fee assigned to the number one key area can be the primary key cost within the database.

increment: This algorithm works with all types of database software but the data type of primary key should be int, short, byte, or long.

sequence: If the series isn't always explicitly described the database uses default series (+1) and every consumer request is then incremented by using +1.

You could also create your very own collection by explicitly growing the collection in the database as follows:

Create series my-collection increment by using 20

You can additionally configure the collection through the use of <param> tag that's a baby tag of <generator> tag.

Sequence algorithm can only be applied to int, short, long, and byte data types.

Sequence algorithm is not supported by all the database software. For example:

Oracles support sequence algorithms but MySQL does not support sequence algorithms. If there is no sequence in the database then the default sequence i.e. HIBERNATE_SEQUENCE is used.

Hilo (high low): It uses a high low algorithm and it uses database data column range.

Default table is hibernate_unique_key and column is next_hi.

native: It uses identity, high low, or sequence algorithms depending on the database vendor.

identity: It is used in MySQL, MS SQL Server, Sybase, DB2 to support the id column. The database is responsible to generate the unique identifier.

sequel: It uses sequence and Hilo algorithms. Its return data type is short, int, long.

UUID: For the generation of id, it uses a 128-bit UUID set of rules. The UUID is represented as hexadecimal digits having a period of 32 characters. It generates an identifier the use of an IP deal with. It's also used to generate passwords.

guide: It only works on MySQL and MS SQL Server.

select: It uses the primary key value returned through database trigger.

foreign: It is mostly used in one-to-one association and uses the id of another associated object.

sequence-identity: It is only supported in Oracle 10g drivers and uses a special sequence generation strategy.

What is Hibernate Algorithm for the primary key?

Can we prove that one can unambiguously construct a binary tree from its in-order and level-order traversals?

I am thinking of a proof by induction on number of levels.

Base case: trees with 1 or 2 levels. These cases are clear.

Assume that this holds for trees with l levels. That is: one can unambiguously construct a binary tree with l levels from its in-order and level-order traversals.

Inductive case: prove that this holds for trees with l+1 levels. Not clear how to proceed in this case. Any help will be appreciated.

Binary tree from in-order and level-order traversals?

IDA* has an algorithm runing inside. Is it the DFS or the Iterative Deepening DFS? Or is it another different algorithm? 

About Artificial Inteligence Search Algorithm

what is the least comparing times for sorting eight numbers in the Tournament sort algorithm?(considering the bad condition)?

The answer is 17 times. But I don't know how to get this answer.And I also want to know whether there is a generalized conclusion?

what is the least comparing times for sorting eight numbers in the Tournament sort algorithm?

given a stack (NOT AN ARRAY) with N elements, what is the most efficient algorithm to shuffle the stack randomly? i.e. given a stack of N songs like in Spotify, what is the best way to shuffle them? 

What is the most optimized algorithm to randomly shuffle a stack?

I am looking to answer two questions in a definitive listing:

What are the underlying data systems used for Redis?

And what are the main blessings/negative aspects/use instances for each kind?

So, I've to study the Redis lists are applied with connected lists. However, for other types, I'm no longer capable of digging up any data. Additionally, if a person were to come upon this question and no longer have a high degree precis of the pros and cons of enhancing or getting access to specific statistics structures, they had had an entire list of when to quality use particular sorts to reference as well.

Mainly, I'm seeking to define every kind: string, list, set, zest and hash.

What are the underlying data structures used for Redis?

I actually want to make a 3rd pt.package compatible to use with Spark. 

 I can't reimplement an algorithm from Python to Scala !

Especially using Holt Winter algorithm..???

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