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NULL Pointer in C - GeeksforGeeks

We just have to assign the NULL value. Strictly speaking, NULL expands to an implementation-defined null pointer constant which is defined in many header files such as “stdio.h”, “stddef.h”, “stdlib.h” etc.

Published: January 10, 2025

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NULL Pointer in C

Checking if the FILE pointer returned by the fopen() function is NULL is always a recommended approach to avoid runtime errors in file-related processing. The following example shows how you can use the NULL file pointer to ensure that a file is accessible or not −

Discussions

Checking for NULL pointer in C/C++ - Stack Overflow

So if you want to check a pointer, better to do "if (ptr != NULL)" instead of "if (ptr)". If you mistakenly declare ptr as an int, the first check will raise a warning/error, while the latter will compile without any warning. 2014-11-05T09:21:23.753Z+00:00 ... @David天宇Wong No, that is not what was meant. The example ... More on stackoverflow.com

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what is a null pointer in c - Stack Overflow

I tried looking online but I didn't know exactly what to type. The Google search results I got for 'NULL pointer' were different from what I expected. ... There is also a typo in n2.next = &n2;, meaning that we will never reach n3. I would just throw this bad example away and study some other code. More on stackoverflow.com

stackoverflow.com

Why do we use Null pointers?

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. More on reddit.com

r/C_Programming

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Trying to understand NULL pointers

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. More on reddit.com

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

March 28, 2023 - 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.

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Null Pointer In C | A Detailed Explanation With Examples

May 3, 2024 - The incorrectUse() function directly dereferences the pointer without checking if it's NULL. This results in undefined behavior because we're attempting to access memory that doesn't exist. This example shows why it is important to check if the NULL pointer was successfully created in dynamic memory allocation.

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What is Null Pointer in C? - Scaler Topics

September 4, 2023 - We can overcome the above problem ... 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....

codecademy.com › docs › pointers › null pointer

C | Pointers | Null Pointer | Codecademy

February 3, 2025 - In C, the NULL pointer is defined in the <stddef.h> header file. It is typically assigned to a pointer to indicate that it is not pointing to any valid memory. #include <stddef.h> pointer_type *pointer_name = NULL; ... In the example, we declare an integer pointer ptr and initialize it to NULL, indicating that it doesn’t point to any valid memory location:

w3schools.com › c › c_null.php

You can compare a pointer to NULL to check if it is safe to use. Many C functions return NULL when something goes wrong. For example, fopen() returns NULL if a file cannot be opened, and malloc() returns NULL if memory allocation fails.

includehelp.com › c-programs › an-example-of-null-pointer-in-c.aspx

An Example of Null pointer in C

March 10, 2024 - ptr1 is initialized with the address of the integer variable num, thus ptr1 contains a valid memory address. ptr2 is uninitialized and ptr3 assigned 0. Thus, ptr2 and ptr3 are the NULL pointers.

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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 - A null pointer points to the 0th memory location, a reserved memory that cannot be dereferenced. In the below example, we create a pointer *ptr and assign a NULL value to the pointer, which means that it does not point to any variable.

lysator.liu.se › c › c-faq › c-1.html

If the (char *) cast were omitted, the compiler would not know to pass a null pointer, and would pass an integer 0 instead. (Note that many Unix manuals get this example wrong.)

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

July 27, 2026 - Learn in this tutorial about the null pointer in C, including its syntax, uses, how to check it, best practices, and examples to write efficient programs.

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NULL Pointer in C Programming with Examples - Sanfoundry

December 31, 2025 - A NULL pointer is a pointer that does not point to any valid memory location. In C, the macro NULL is defined in several standard header files, such as stdio.h, stddef.h, and stdlib.h, and is typically set to ((void*)0) or 0.

en.wikipedia.org › wiki › Null_pointer

Null pointer - Wikipedia

June 13, 2026 - In practice, dereferencing a null pointer may result in an attempted read or write from memory that is not mapped, triggering a segmentation fault or memory access violation. This may manifest itself as a program crash, or be transformed into a software exception that can be caught by program code. There are, however, certain circumstances where this is not the case. For example...

C C++Other languages Null dereferencing Mitigation History

gnu.org › software › c-intro-and-ref › manual › html_node › Null-Pointers.html

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.

stackoverflow.com › questions › 3825668 › checking-for-null-pointer-in-c-c

Checking for NULL pointer in C/C++ - Stack Overflow

In my experience, tests of the form if (ptr) or if (!ptr) are preferred. They do not depend on the definition of the symbol NULL. They do not expose the opportunity for the accidental assignment. And they are clear and succinct.

Edit: As SoapBox points out in a comment, they are compatible with C++ classes such as unique_ptr, shared_ptr, auto_ptr that are objects that act as pointers and which provide a conversion to bool to enable exactly this idiom. For these objects, an explicit comparison to NULL would have to invoke a conversion to pointer which may have other semantic side effects or be more expensive than the simple existence check that the bool conversion implies.

I have a preference for code that says what it means without unneeded text. if (ptr != NULL) has the same meaning as if (ptr) but at the cost of redundant specificity. The next logical thing is to write if ((ptr != NULL) == TRUE) and that way lies madness. The C language is clear that a boolean tested by if, while or the like has a specific meaning of non-zero value is true and zero is false. Redundancy does not make it clearer.

if (foo) is clear enough. Use it.

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

includehelp.com › c › null-pointer.aspx

NULL pointer in C - IncludeHelp

In the given statement ptr is an integer pointer which is being initialized with NULL, thus ptr will be considered as NULL pointer.

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Null Pointer in C Language - PiEmbSysTech - Embedded Systems & VLSI Lab

September 15, 2023 - Sentinel Values: In data structures like linked lists, null pointers can serve as sentinel values to indicate the end of the list or the absence of a linked element. struct Node { int data; struct Node *next; }; struct Node *head = NULL; // ...

uncodemy.com › blog › null-pointer-in-c-and-c-plus-plus-meaning-and-usage

Null Pointer in C and C++: Meaning and Usage

1 month ago - This means ptr is not pointing to any valid memory address. Instead, it’s been given a special, reserved value (NULL or 0) that says, “This pointer is empty or uninitialized.” · At first glance, assigning a pointer to "nothing" might seem odd. Why would you deliberately create a pointer that points nowhere?