Some uses of the null pointer are: a) To initialize a pointer variable when that pointer variable isn’t assigned any valid memory address yet. 2) Unlike normal pointers, we do not allocate de-allocate memory using function pointers. A pointer that is not assigned any value but NULL is known as the NULL pointer. Qual è la differenza tra NULL, '\ 0' e 0 ... il carattere speciale chiamato "NUL" o "NULL". printf("Address of the given pointer variable: %d", pointer_var); The null pointer basically stores the Null value while void is the type of the pointer. Explanation: In the above code, we are defining function func() where we are passing a pointer ptrvarA and when the function func() is called it checks if the passed pointer is a null pointer or not. Pointers in C programming language is a variable which is used to store the memory address of another variable. if(pointer_var!=NULL) In Functions Pointers, function’s name can be used to get function’s address. 4) Like normal pointers, we can have an array of function pointers. It inherits from integral_constant as being either true_type or false_type. For this article, I am assuming that you have basic knowledge of function pointers. void func(int *ptrvarB) { To do so, you would have to declare a function returning a pointer as in the following example − int * myFunction() { . So we have to check if the passed value of the pointer is null or not because if it is not assigned to any value it will take the garbage value and it will terminate your program which will lead to the crashing of the program. The C standard defines a NULL pointer as a pointer with the value 0. 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 C, NULL is a symbolic constant that always points to a nonexistent point in the memory. And also note that never declare any pointer without assigning NULL because the program when executes it throws an error during runtime. With pointer parameters, our functions now can process actual data rather than a copy of data. The above search function can be used for any data type by writing a separate customized compare(). NULL however is used differently from other languages. //Handle NULL pointer input How do I “get” a null pointer … A pointer that is assigned NULL is called a null pointer.The NULL pointer is a constant with a value of zero defined in several standard libraries. Function Pointers point to code like normal pointers. Why do we need an extra bracket around function pointers like fun_ptr in above example? The null pointer usually does not point to anything. Example: It stores the base address of the segment. How to declare a pointer to a function? brightness_4 b) To pass a null pointer to a function argument when we don’t want to pass any valid memory address. close, link Once the address of a function is assigned to a pointer variable (function pointer), Then the respective function pointer can be used to access the function. Note that this trait only classifies the type of T, not whether the potential value of a pointer is a null pointer value. NULL pointer. In case with the pointers - if any pointer does not contain a valid memory address or any pointer is uninitialized, known as "NULL pointer". Similar to qsort(), we can write our own functions that can be used for any data type and can do different tasks without code redundancy. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. int * pointer_var =NULL; And we should note that once the data is not in use the memory allocated to it must be freed else it will again lead to the dangling pointer. To avoid this exception we can rewrite the above code as, #include  else The macro NULL is an implementation-defined null pointer constant, which may be an integer constant expression with the value ​0​ an integer constant expression with the value 0 cast to the type void* A null pointer constant may be converted to any pointer type; such conversion results in the null pointer value of that type. “ An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. return 0; return 0; What is this infamous null pointer, anyway? For example a simple qsort() function can be used to sort arrays in ascending order or descending or by any other order in case of array of structures. generate link and share the link here. Following is a simple example where we pass an unsigned long pointer to a function and change the value inside the function which reflects back in the calling function − int main() How to write C functions that modify head pointer of a Linked List? Writing code in comment? In C programming language NULL is a macro constant that is defined in a few of the header files like stdio.h, alloc.h, mem.h, stddef.h, stdlib.h. 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. Avoid Crashing a Program: If you pass any garbage value in your code or to the particular function, your program can crash. { We can notice here that the function pointer is used to implement different functions which are similar in their structure. Below example in point 5 shows syntax for array of pointers. This is done at the time of variable declaration. What is the use of NULL Pointer in C? A null pointer in C is a pointer that is assigned to zero or NULL where a variable that has no valid address. { A null pointer is a special reserved value which is defined in a stddef header file. Function Pointers in the Wild Let's go back to the sorting example where I suggested using a function pointer to write a generic sorting routine where the exact order could be specified by the programmer calling the sorting function. C/C++ Null Pointers Section 1. So we use keyword NULL to assign a variable to be a null pointer in C it is predefined macro. Here are some use cases of NULL pointer… 1. Not only this, with function pointers and void pointers, it is possible to use qsort for any data type. By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy, Special Offer - C Programming Training Course Learn More, C Programming Training (3 Courses, 5 Project), 3 Online Courses | 5 Hands-on Projects | 34+ Hours | Verifiable Certificate of Completion | Lifetime Access, C++ Training (4 Courses, 5 Projects, 4 Quizzes), Java Training (40 Courses, 29 Projects, 4 Quizzes), Software Development Course - All in One Bundle. But, they are one of the features which make C an excellent language. The Null pointer is a special pointer that does not point to any valid memory address. printf("It is not a null pointer"); In C, dal momento che non dovresti incorporare caratteri di controllo nel tuo codice sorgente, questo è rappresentato in stringhe C con uno 0 sfuggito, cioè "\ 0". In C programming language, a variable that can point to or store the address of another variable is known as pointers. { int *pointer_var; }. { If the file pointer is null, print “Sorry. { In C function pointer is like a normal pointer which is points some piece of the code that is used in runtime binding and resolves many problems. In C programming language NULL is a macro constant that is defined in a few of the header files like stdio.h, alloc.h, mem.h, stddef.h, stdlib.h. If we remove bracket, then the expression “void (*fun_ptr)(int)” becomes “void *fun_ptr(int)” which is declaration of a function that returns void pointer. Experience. Pointers give greatly possibilities to 'C' functions which we are limited to return one value. To avoid this, you can use NULL pointer. Typically a function pointer stores the start of executable code. So to avoid such situations we use null pointers where variables are assigned or declared as NULL or zero which is known as a null pointer. #include Although many programmers treat it as equal to 0, this is a simplification that can trip you up later on. In general, we can a pointer that does not point to any object is known as a null pointer. First, initialize character variable s and two integer variables i and n where n=1. ALL RIGHTS RESERVED. NULL pointer in C. A null pointer is a pointer which points nothing. } So there is a way to check for the pointer is null or not by using if(ptr) results in 1 if the pointer is not null and if(!ptr)  results in 1 when the pointer is null as we did in the above-modified program. int main() Trait class that identifies whether the type of T is nullptr_t. This article is contributed by Abhay Rathi. { Following are some interesting facts about function pointers. 3) A function’s name can also be used to get functions’ address. We have seen in the last chapter how C programming allows to return an array from a function. Similarly, C also allows to return a pointer from a function. 7) Many object oriented features in C++ are implemented using function pointers in C. For example virtual functions. This point in particular is very useful in C. In C, we can use function pointers to avoid code redundancy. 2. A null pointer in c programming is a pointer that is showing or pointing nothingit is a pointer that tries to point the bottom address of a certain section in the computer memory A null pointer is also said to be a value that is false; this can be illustrated by using numbers which are a computer language, for example, 6>9, in computer language this statement is said to be null pointing. { }. Simple syntax for declaring NULL pointer is as follows: Start Your Free Software Development Course, Web development, programming languages, Software testing & others. In general computer programming a null pointer is a pointer that does not point to any object or function. } A user can use this structure to store the address of a function using the function pointer as per the requirements and called this function whenever required in the program. . THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. . In C, NULL is limited to identifying a null pointer. int main () To do so, simply declare the function parameter as a pointer type. Null Pointers. Pointers are arguably the most difficult feature of C to understand. Earlier I mentioned that the mmap() function returns the constant MAP_FAILED in case of an error, and that this constant is … else if(ptrvarB == NULL) We can directly assign the pointer variable to 0 to make it null pointer. We can use it to initialize a pointer variable when that pointer variable isn’t … The null pointer usually does not point to anything. A null pointer in C is a pointer that is assigned to zero or NULL where a variable that has no valid address. NULL Pointer: The integer constant zero(0) has different meanings depending upon it’s used.In all cases, it is an integer constant with the value 0, it is just described in different ways. This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. If any pointer is being compared to 0, then this is a check to see if the pointer is a null pointer.This 0 is then referred to as a null pointer constant. Below is an example search function that can be used for any data type. 6) Like normal data pointers, a function pointer can be passed as an argument and can also be returned from a function. For example, in below program, user is asked for a choice between 0 and 2 to do different tasks. C Pointer and Functions A function pointer is nothing more than a variable that stores the address of a function. Details Last Updated: 06 December 2020 . Functions Pointers in C Programming with Examples . A Null Pointer is a pointer that does not point to any memory location. It … How does Null pointer work in C? #include functions - pointers in c . In most of the examples, a null pointer is used to denote or indicate the end of the list. In most of 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. The above search function can be used for any data type by writing a separate customized compare(). But it is not recommended to return the address of a local variable outside the function as it goes out of scope after function returns. edit For de-allocating memory of the C dangling pointer concept, free() function is used with a single parameter just to make a pointer into a dangling pointer. In C, like normal data pointers (int *, char *, etc), we can have pointers to functions. printf("Invalid pointer"); It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. So usually when we try to write or read from a null pointer we get 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 null pointer exception. For example, in the below program, we have removed address operator ‘&’ in assignment. Attention reader! The file you are trying to open do not exist . Don’t stop learning now. Class methods are another example implemented using function pointers. }. Assigning the NULL value to the specific pointer helps the pointer not pointing to any specific memory location. Let us see an example of how null pointers are created. In C programming language a Null pointer is a pointer which is a variable with the value assigned as zero or having an address pointing to nothing. Get hold of all the important C++ Foundation and STL concepts with the C++ Foundation and STL courses at a student-friendly price and become industry ready. Explanation: In the above code, the pointer_var variable is not assigned to zero nor it stores 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. This is a guide to Null pointer in C. Here we discuss how Null pointer work in C  with syntax and examples to implement with proper codes and outputs. So by default, we can say that if a pointer is assigned to zero then it is nothing but it only points to nothing. Refer this book for more details. Member types C programming allows passing a pointer to a function. When we initialize a pointer, we might not always know what it points to. http://www.cs.cmu.edu/~ab/15-123S11/AnnotatedNotes/Lecture14.pdf, http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-087-practical-programming-in-c-january-iap-2010/lecture-notes/MIT6_087IAP10_lec08.pdf, http://www.cs.cmu.edu/~guna/15-123S11/Lectures/Lecture14.pdf. { printf("Value of pointer variable is : %d",* pointer_var); We can also assign 0 (or NULL) to make a pointer as "NULL pointer". Please use ide.geeksforgeeks.org, Passing by pointer Vs Passing by Reference in C++, Data Structures and Algorithms – Self Paced Course, Ad-Free Experience – GeeksforGeeks Premium, We use cookies to ensure you have the best browsing experience on our website. In other words, a null pointer refers to a pointer variable that does not point to a valid address. The Null pointer is, therefore, assigned to constant NULL. A: For each pointer type, there is a special value — the “null pointer” — which is distinguishable from all other pointer values and which is not the address of any object. If the file pointer is not null, execute the for loop that checks whether i 1. Following is a simple example that shows declaration and function call using function pointer. You can also go through our other related articles to learn more –, All in One Software Development Bundle (600+ Courses, 50+ projects). How to return a Pointer from a Function in C, Multidimensional Pointer Arithmetic in C/C++. We can pass pointers to the function as well as return pointer from a function. 5) Function pointer can be used in place of switch case. © 2020 - EDUCBA. Suppose let us take another example where the pointer variables are not assigned to any memory address. The word "NULL" is a constant in C language and its value is 0. That’s when it is useful: code. So relax, grab a coffee, and Let us see the use of null pointers in C programming language as below: Null pointers are used to avoid crashing down of the program: As we saw earlier if we declare any pointer without assigning anything to it then it takes garbage value where it may result in crashing of the system program. Explanation: In the above code, we are initializing the variable “ptr”  to 0 (zero) so when we print the pointer value which Null pointer. Like C++, in C language we cannot create a member function in the structure but with the help of pointer to a function, we can provide the facility to the user to store the address of the function.