{ 5) Function pointer can be used in place of switch case. A pointer that is not assigned any value but NULL is known as the NULL pointer. 1. A null pointer in C is a pointer that is assigned to zero or NULL where a variable that has no valid address. The null pointer usually does not point to anything. { We can use it to initialize a pointer variable when that pointer variable isn’t … } What is the use of NULL Pointer in C? NULL pointer. Pointers give greatly possibilities to 'C' functions which we are limited to return one value. For example, consider the following C program where wrapper() receives a void fun() as parameter and calls the passed function. generate link and share the link here. }. { Example: In most of the examples, a null pointer is used to denote or indicate the end of the list. else printf("Value of pointer variable is : %d", * pointer_var); { C programming allows passing a pointer to a function. Member types So relax, grab a coffee, and THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. 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. We can pass pointers to the function as well as return pointer from a function. printf("Value of pointer variable is : %d",* pointer_var); printf("The value of pointer assigned is : %x\n", ptr  ); If the file pointer is null, print “Sorry. Refer this book for more details. 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. See following post for details. When we initialize a pointer, we might not always know what it points to. To avoid this, you can use NULL pointer. { 1) Unlike normal pointers, a function pointer points to code, not data. Assigning the NULL value to the specific pointer helps the pointer not pointing to any specific memory location. } Function pointer as argument in C with Tutorial, C language with programming examples for beginners and professionals covering concepts, c array, c pointers, c structures, c union, c strings etc. printf("Invalid pointer"); { Below is an example search function that can be used for any data type. The above search function can be used for any data type by writing a separate customized compare(). What is this infamous null pointer, anyway? else . C/C++ Null Pointers Section 1. printf("It is null pointer"); A null pointer in C is a pointer that is assigned to zero or NULL where a variable that has no valid address. In this article, we will go from the very basics of pointers to their usage with arrays, functions, and structure. Although many programmers treat it as equal to 0, this is a simplification that can trip you up later on. To avoid this exception we can rewrite the above code as, #include  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. 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. . 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. return 0; code. So by default, we can say that if a pointer is assigned to zero then it is nothing but it only points to nothing. Not only this, with function pointers and void pointers, it is possible to use qsort for any data type. Why do we need an extra bracket around function pointers like fun_ptr in above example? 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. If the file pointer is not null, execute the for loop that checks whether i int main() Following are some interesting facts about function pointers. 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. 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. Don’t stop learning now. 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. In case with the pointers - if any pointer does not contain a valid memory address or any pointer is uninitialized, known as "NULL pointer". //Handle NULL pointer input { int *pointer_var; The C standard defines a NULL pointer as a pointer with the value 0. © 2020 - EDUCBA. In general, we can a pointer that does not point to any object is known as a null pointer. } Note that this trait only classifies the type of T, not whether the potential value of a pointer is a null pointer value. 4) Like normal pointers, we can have an array of function pointers. close, link int main () 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. Details Last Updated: 06 December 2020 . if(pointer_var!=NULL) Functions Pointers in C Programming with Examples . edit For example, in the below program, we have removed address operator ‘&’ in assignment. Class methods are another example implemented using function pointers. This point in particular is very useful in C. In C, we can use function pointers to avoid code redundancy. Earlier I mentioned that the mmap() function returns the constant MAP_FAILED in case of an error, and that this constant is … The Null pointer is, therefore, assigned to constant NULL. “ An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. Avoid Crashing a Program: If you pass any garbage value in your code or to the particular function, your program can crash. It inherits from integral_constant as being either true_type or false_type. 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. The null pointer usually does not point to anything. 3) A function’s name can also be used to get functions’ address. 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 Functions Pointers, function’s name can be used to get function’s address. Trait class that identifies whether the type of T is nullptr_t. The file you are trying to open do not exist . Related Article:Pointers in C and C++ | Set 1 (Introduction, Arithmetic and Array), References: Then, open the text file in the specified location write mode. We have seen in the last chapter how C programming allows to return an array from a function. Simple syntax for declaring NULL pointer is as follows: Start Your Free Software Development Course, Web development, programming languages, Software testing & others. ALL RIGHTS RESERVED. 2) Unlike normal pointers, we do not allocate de-allocate memory using function pointers. In other words, function pointers are useful when a program has polymorphism. How do I “get” a null pointer … How does Null pointer work in C? }. b) To pass a null pointer to a function argument when we don’t want to pass any valid memory address. Pointers are arguably the most difficult feature of C to understand. Explanation: In the above code, we are initializing the variable “ptr”  to 0 (zero) so when we print the pointer value which Null pointer. Please use ide.geeksforgeeks.org, 7) Many object oriented features in C++ are implemented using function pointers in C. For example virtual functions. In general computer programming a null pointer is a pointer that does not point to any object or function. 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. You can also go through our other related articles to learn more –, All in One Software Development Bundle (600+ Courses, 50+ projects). } Output: Returned index is 2. First, initialize character variable s and two integer variables i and n where n=1. It … 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. { 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. The null pointer basically stores the Null value while void is the type of the pointer. In this article, we are discussing the null pointer in C, where NULL is constant with value 0 in C. So the null pointer is defined as the pointer that is assigned to zero to make it null pointer or a pointer that does not store any valid memory address or an uninitialized pointer are known as a NULL pointer.