Interview Questions on Pointers in C
The C programming language's foundational idea of pointers enables direct manipulation and access to memory locations. They offer a means of storing and managing memory addresses, facilitating effective memory allocation and indirect data access.
Each variable in C has a unique memory address and is maintained in memory. A pointer is a variable that stores the location of another variable in memory. The information "points" to the location in memory where it is stored.
These C pointers interview questions and their responses are provided here.
Question 1. What does a pointer in C mean?
Answer. A pointer is a C term for a variable that stores the memory address of another variable. It enables immediate access to and control over the data in that memory location.
Question 2. How do you declare a pointer variable in C?
Answer. An asterisk (*) is used before the variable name to indicate that it is a pointer variable. For instance, the statement ‘int *ptr;’ declares an integer pointer.
Question 3. What does it mean to dereference a pointer?
Answer. Dereferencing a pointer entails getting at the value kept at the memory address the pointer is pointing to. The dereference operator (*) is used before the pointer variable. For instance, *ptr returns the value stored at the memory address ptr referred to.
Question 4. What is the size of a pointer variable in C?
Answer. The size of a pointer variable depends on the system architecture. On average, a 64-bit system uses 8 bytes, while a 32-bit system uses 4.
Question 5. How do an array and a pointer vary from one another?
Answer. A pointer is a variable that stores the memory address of another variable. In contrast, an array is a continuous block of memory that contains several objects of the same kind. An array name may be used with a constant pointer to the array's first element.
Question 6. How do you use pointers to allocate memory in C dynamically?
Answer. Memory may be allocated dynamically using the malloc() and calloc() functions. While calloc() allots and initializes the memory to zero, malloc() creates a memory block of a given size. The allocated memory should be released using the free() method when no longer required.
Question 7. What are the advantages of using pointers in C?
Answer. Pointers enable effective memory management, dynamic memory allocation, parameter passing by reference, and the construction of intricate data structures like linked lists and trees.
Question 8. How may pointers be used to explain passing arguments by reference?
Answer. When you pass arguments by reference, you give a function a variable's memory address rather than its value. The modifications made by changing the value there will be seen outside the function. In C, pointers are utilized to do this.
Question 9. What is the C syntax for a function returning a pointer?
Answer. The function's return type must be a pointer type to return a pointer. The pointer can be either a static or a local variable (allocated dynamically). Ensuring the returned pointer is still valid once the function is finished is crucial.
Question 10. How do void and null pointers vary from one another?
Answer. A void pointer (void*) is a general-purpose pointer that may store the address of any object but cannot be directly dereferenced. An exceptional value, such as 0 or NULL, is set when a pointer variable doesn't point to anything worthwhile.
Question 11. What is the significance of the "const" keyword when used with pointers?
Answer. When the word "const" is used with pointers, the value the pointer points to is fixed and cannot be changed. It aids in enforcing read-only access to the data and guards against accidental alterations.
Question 12. A pointer may point at another pointer. If so, give a concrete example.
Answer. Undoubtedly, one pointer can point to another. A double pointer or pointer to a pointer is what is being used here. When the statement int **ptr; is used, for example, a double pointer that may hold the address of a pointer variable is defined.
Question 13. What are function pointers in C? How are they useful?
Answer. Function pointers keep track of a function's address. They enable the construction of function tables and callbacks in advanced C programming and the dynamic selection and invocation of various functions during runtime.
Question 14. How does pointer arithmetic work in C?
Answer. Based on the data type size the pointer points to, pointer arithmetic in C enables incrementing or decrementing a pointer by a certain number of elements. For instance, ptr++ will advance the pointer to the following integer element if ptr is an int* pointer.
Question 15. What does a double-pointer mean? Why would you use it?
Answer. Double pointers are markers that also point to additional markers. It's used when working with dynamic memory allocation or when directly changing a pointer variable inside of a function. It is widely used, for example, when working with linked lists or multi-dimensional arrays.
Question 16. Describe memory leaks in C and how to prevent them.
Answer. When dynamically allocated memory is improperly deallocated, it causes RAM to become unavailable for reuse and causes memory leaks. Always release dynamically created memory using the free() method when it is no longer required to prevent memory leaks or provide adequate cleaning in the event of early function returns or failures.
Question 17. What are dangling pointers? How can you prevent them?
Answer. Pointers that point to invalid or deallocated memory are referred to as dangling pointers. They can happen if a pointer is misused after the memory it points to has been released or improperly initialized. Avoid using pointers after the memory associated with them has been released, and initialize pointers before using them to prevent dangling pointers.
Question 18. Can you have a function pointer in C? If so, give an illustration.
Answer. In C, a pointer to a function is indeed conceivable. The memory address of a function is stored by use of function pointers. The function pointer can be used to call them at a later time. For instance: It declares a function pointer named funcPtr, which can point to a function with no parameters and a void return type using the syntax void (*funcPtr)().
19. How are structure pointers created and used in C?
Answer. In C, you must first declare a structure using the struct keyword before building a structure pointer. Then, use the structure name and the * symbol to declare a pointer variable of that structure type. Use the arrow operator (->) rather than the dot operator to use a pointer to structural members.
20. What differentiates a constant pointer from a pointer to a constant?
Answer. An unchangeable pointer after initialization is known as a constant pointer. The value it points to, nevertheless, is adjustable. On the other hand, a pointer that points to a constant can be moved to other addresses, but the value it refers to cannot be changed using that reference.