Q.1 What is the difference between declaration and definition of a variable /function.
Q.2 What is scope of a variable? How are variables scoped in C?
Q.3 What are different storage class specifiers in C?
Answer: auto, register, static, extern
Q.4 What is NULL pointer?
Q.5 What is memory leak? Why it should be avoided
Q.7 What is Dangling pointer?
Answer: Declaration of a variable/function simply declares that the variable/function exists somewhere in the program but the memory is not allocated for them. But the declaration of a variable/function serves an important role. And that is the type of the variable/function. Therefore, when a variable is declared, the program knows the data type of that variable. In case of function declaration, the program knows what are the arguments to that functions, their data types, the order of arguments and the return type of the function. So that’s all about declaration. Coming to the definition, when we define a variable/function, apart from the role of declaration, it also allocates memory for that variable/function. Therefore, we can think of definition as a super set of declaration. (or declaration as a subset of definition).
// This is only declaration. y is not allocated memory by this statementextern int y;
// This is both declaration and definition, memory to x is allocated by this statement.
int x;
Q.2 What is scope of a variable? How are variables scoped in C?
Answer: Scope of a variable is the part of the program where the variable may directly be accessible. In C, all identifiers are lexically (or statically) scoped. See this for more details.
Answer: auto, register, static, extern
Q.4 What is NULL pointer?
Answer: NULL is used to indicate that the pointer doesn’t point to a valid location. Ideally, we should initialize pointers as NULL if we don’t know their value at the time of declaration. Also, we should make a pointer NULL when memory pointed by it is deallocated in the middle of a program.
Answer: Memory leak occurs when programmers create a memory in heap and forget to delete it. Memory leaks are particularly serious issues for programs like daemons and servers which by definition never terminate.
/* Function with memory leak */#include <stdlib.h>
void f()
{
int* ptr = (int*)malloc(sizeof(int));
/* Do some work */
return; /* Return without freeing ptr*/
}
Q.6 What are static functions? What is their use?
Answer: In C, functions are global by default. The “static” keyword before a function name makes it static. Unlike global functions in C, access to static functions is restricted to the file where they are declared. Therefore, when we want to restrict access to functions, we make them static. Another reason for making functions static can be reuse of the same function name in other files. See this for examples and more details.
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Q.7 What is Dangling pointer?
Answer: Dangling Pointer is a pointer that doesn’t point to a valid memory location. Dangling pointers arise when an object is deleted or deallocated, without modifying the value of the pointer, so that the pointer still points to the memory location of the deallocated memory.
