Null pointer

a value indicating that a pointer does not refer to a valid object

In computing, a null pointer (sometimes shortened to nullptr or null) or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. … Wikipedia

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Null pointer - Wikipedia

3 weeks ago - For example, in x86 real mode, the address 0000:0000 is readable and also usually writable, and dereferencing a pointer to that address is a perfectly valid but typically unwanted action that may lead to undefined but non-crashing behavior in the application; if a null pointer is represented as a pointer to that address, dereferencing it will lead to that behavior. There are occasions when dereferencing a pointer to address zero is intentional and well-defined; for example, BIOS code written in C for 16-bit real-mode x86 devices may write the interrupt descriptor table (IDT) at physical address 0 of the machine by dereferencing a pointer with the same value as a null pointer for writing.

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geeksforgeeks.org › c language › null-pointer-in-c

NULL Pointer in C - GeeksforGeeks

As the value of NULL in predefined libraries is 0 and the pointer (that's pointing to NULL) is not pointing to any memory location, this behavior occurs. We can pass a NULL value for pointers that should not contain any value to the function in C.

Published January 10, 2025

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NULL Pointer in C

A NULL pointer in C is a pointer that doesn't point to any of the memory locations. The NULL constant is defined in the header files stdio.h, stddef.h as well as stdlib.h.

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Null Pointer In C | A Detailed Explanation With Examples // Unstop

May 3, 2024 - A null pointer in C does not point to any memory location. They are used in dynamic memory allocation, error handling, initialization of other pointers and more.

stackoverflow.com › questions › 49712466 › what-is-a-null-pointer-in-c

what is a null pointer in c - Stack Overflow

Any pointer type with the value 0 is called a null pointer. Here is the explanation from the C standard §6.3.2.3:

An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function

Null pointer is a pointer that points to memory address 0. Most system reserve this address so that no object will ever reside in there. This reservation allows to use it as blank address.

If you try to read or write from null pointer you will get runtime error which is sometimes called segmentation fault, or null pointer exception.

In your example the null pointer is used to indicate end of the list. So this condition (struct entry *) 0, checks if you have reached end of the list and iteration should stop

Usually it considered better form to use constant NULL instead of literal value 0. This makes code more readable, and also covers very rare case when NULL pointer is not a 0

The cast (struct entry *) is just to avoid compiler warning, because literal 0 is of type integer not a pointer. That's another reason to use constant NULL, because it is usually defined as (void*) 0 which compares nicely to any pointer value without a warning from compiler

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What is Null Pointer in C? - Scaler Topics

November 9, 2022 - A null pointer refers to the 0th memory location, which is a shared memory area that can't be dereferenced. In the example below, We create a pointer *ptr and assign it the value NULL to indicate that it doesn't point to any variables.

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Null pointer in C | How Null pointer work in C with Examples

March 28, 2023 - In C programming language pointers are used to point to the memory that is allocated dynamically or at run time and a pointer can be of any data type like int, float, char, etc. In this article, we are discussing the null pointer in C, where NULL is constant with value 0 in C.

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Null Pointer in C - javatpoint

Null Pointer in C with programming examples for beginners and professionals covering concepts, control statements, c array, c pointers, c structures, c union, c strings and more.

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Null Pointer in C Language with Examples - Dot Net Tutorials

November 16, 2023 - Dereferencing: Dereferencing a null pointer leads to undefined behavior, often resulting in a runtime error or a program crash. The pointer variable, initialized with the null value, is called the Null Pointer. Null Pointer doesn’t point to ...

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Using Null Pointer in C Programming

A null pointer is a pointer that does not point to any memory address. In C programming, a null pointer is represented by the constant NULL, which is defined in the header file stdio.h.

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Null Pointer in C Language (Uses, Best Practices, Examples)

August 29, 2025 - Learn about the null pointer in C language, including its syntax, uses, how to check it, best practices, examples, and more. Read now!

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NULL Pointer | C Tutorial | CodeWithHarry

In contrast, an uninitialized pointer means that the pointer occupies a garbage value address. The garbage value address is still a real memory location and hence not a NULL value. So to be on the safe side, NULL pointers are preferred. NULL pointers and void pointers very much sound similar just because of their nomenclatures, but they are very different as a NULL pointer is a pointer with a NULL value address, and a void pointer is a pointer of void data type.

reddit.com › r/c_programming › why do we use null pointers?

r/C_Programming on Reddit: Why do we use Null pointers?

August 30, 2024 -

If we want to "Nullify" something why dont we create a pointer in a controlled way that points to value 0?

The value where a null pointer is pointing is irrelevant. A null pointer is a pointer that is pointing nowhere--there is no value. In C, the number 0 was defined as the representation of the null pointer. They could have picked any number, but it would have been painful.

What do you mean by pointing to 0? NULL is the address 0x0 An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.

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NULL Pointer in C Programming with Examples - Sanfoundry

April 17, 2025 - This C Tutorial Explains NULL Pointer in C with Examples. It is a type of pointer that doesn’t point to any memory location, but the zeroth memory location.

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Null Pointers (GNU C Language Manual)

A pointer value can be null, which means it does not point to any object. The cleanest way to get a null pointer is by writing NULL, a standard macro defined in stddef.h. You can also do it by casting 0 to the desired pointer type, as in (char *) 0.

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C Examples C Real-Life Examples C Exercises C Quiz C Compiler C Syllabus C Study Plan C Interview Q&A C Certificate ... NULL is a special value that represents a "null pointer" - a pointer that does not point to anything.

reddit.com › r/learnprogramming › trying to understand null pointers

r/learnprogramming on Reddit: Trying to understand NULL pointers

December 30, 2021 -

Hello all again,

I have another stupid question here lol, so I'm trying to wrap my head around NULL. Im currently under the impression that NULL is a built in constant that has a value of zero, but what does that actually mean? When would it be appropriate to use null? If someone could explain it in layman's terms that would be super helpful!

NULL is equivalent to 0 and equivalent to nullptr (in C++). It's an address that is "universally invalid." You can store 0x2093704802934 in a pointer and it will be invalid too (I'm sure) but it's not a convention. NULL is this convention that says "the pointer is not valid" and/or "the pointer hasn't been initialized yet" or "the memory pointed to has been released and I have invalidated the pointer by setting it to NULL." You store this value in a "pointer", like "int* s = 0" to show that it is not pointing to anything. And in your code you will check whether the pointer (s in my example) is equal to NULL (invalid) or not (valid). First you create a pointer, then you initialize it, then you use it, then you release it.

NULL is better thought of as a value of "nothing" rather than a value of zero. Using numbers is a good way to explain it, though. Say you want to accept an integer. Well most languages default new integers at 0. But then say you want 0 to mean something different than the person not supplying a number at all (e.g. undefined or null). Then you could accept a pointer to an integer instead. That pointer could be to an actual number (e.g. 0 or 1), but also to NULL to mean "nothing" (or undefined, or give me the default behavior, or whatever the program defines it as).

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10.4 Null Pointers

A function that returns pointer values can return a null pointer when it is unable to perform its task. (A null pointer used in this way is analogous to the EOF value that functions like getchar return.) As an example, let us write our own version of the standard library function strstr, which looks for one string within another, returning a pointer to the string if it can, or a null pointer if it cannot.

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Null Pointer in C - Naukri Code 360

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Null Pointer - an overview | ScienceDirect Topics

We will now create a classic NULL pointer example, the most typical problem with programs. NULL pointers can lead to all kinds of unexpected behavior, including kernel crashes. Our program, called null-pointer.c, now looks like this: Copyright ©Intel Corporation.