What Happens If You Free A NULL Pointer?

Is null a keyword in C?

Traditionally, the NULL macro is an implementation defined constant representing a null pointer, usually the integer 0 .

In C, the NULL macro can have type void * .

However, in C++ this definition is invalid, as there is no implicit cast from a void * type to any other pointer type (which C allows)..

What is the use of NULL pointer?

A null pointer has a reserved value that is called a null pointer constant for indicating that the pointer does not point to any valid object or function. You can use null pointers in the following cases: Initialize pointers. Represent conditions such as the end of a list of unknown length.

Can Free Be Applied on NULL pointer?

Explanation: free() can be called for NULL pointer, so no problem with free function call.

Why are null pointers bad?

NULL is difficult to debug Calling member functions on a NULL pointer won’t necessarily crash the program. It’s much worse: it might crash the program. … Since bar doesn’t dereference that NULL pointer, it succeeds. But baz does, which causes a segmentation fault.

What is the meaning of null?

adjective. without legal force; invalid; (esp in the phrase null and void) without value or consequence; useless. lacking distinction; characterlessa null expression. nonexistent; amounting to nothing.

Does Delete Delete a pointer?

delete() in C++ Delete is an operator that is used to destroy array and non-array(pointer) objects which are created by new expression. … Pointer to object is not destroyed, value or memory block pointed by pointer is destroyed.

Can you dereference a NULL pointer?

A NULL pointer dereference is a sub type of an error causing a segmentation fault. It occurs when a program attempts to read or write to memory with a NULL pointer. Running a program that contains a NULL pointer dereference generates an immediate segmentation fault error.

IS NULL pointer same as uninitialized pointer?

NULL vs Uninitialized pointer – An uninitialized pointer stores an undefined value. A null pointer stores a defined value, but one that is defined by the environment to not be a valid address for any member or object.

Why do be need NULL pointer in C?

A null pointer is a pointer which points nothing. 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. b) To pass a null pointer to a function argument when we don’t want to pass any valid memory address.

What happens if you dereference a NULL pointer?

Dereferencing a null pointer always has undefined behavior and can cause crashes. If the compiler spots a pointer dereference, it treats that pointer as non-null. As a result, null equality checks on pointers that are guaranteed to be dereferenced may be optimized away.

Can we return NULL in C?

As long as 0 is not a valid return value, NULL is fine to return for a pointer value, if it makes logical sense. The nice thing is that NULL reads as false in a conditional evaluation. The sticking point is when NULL becomes a catch-all for multiple different kinds of values in a program.

What is a void pointer?

The void pointer in C is a pointer which is not associated with any data types. It points to some data location in the storage means points to the address of variables. It is also called general purpose pointer. In C, malloc() and calloc() functions return void * or generic pointers.

Can we use delete with malloc?

You can use malloc() and new in the same program. But you cannot allocate an object with malloc() and free it using delete . Nor can you allocate with new and delete with free() or use realloc() on an array allocated by new .

Is 0 and null the same?

‘\0’ is defined to be a null character. It is a character with all bits set to zero. This has nothing to do with pointers. ‘\0’ is (like all character literals) an integer constant with the value zero.

Is null a keyword?

The null keyword is a literal that represents a null reference, one that does not refer to any object. null is the default value of reference-type variables. Ordinary value types cannot be null, except for nullable value types.

How is NULL defined in C?

The C library Macro NULL is the value of a null pointer constant. It may be defined as ((void*)0), 0 or 0L depending on the compiler vendor.

What happens when delete is used for a null pointer?

What happens when delete is used for a NULL pointer? Explanation: Deleting a null pointer has no effect, so it is not necessary to check for a null pointer before calling delete.

IS NULL == Nullptr?

Nullptr vs NULL NULL is 0 (zero) i.e. integer constant zero with C-style typecast to void* , while nullptr is prvalue of type nullptr_t , which is an integer literal that evaluates to zero.

What is null point?

In physics a null is a point in a field where the field quantity is zero as the result of two or more opposing quantities completely cancelling each other. The field may be scalar, vector or tensor in nature.

Is it good idea to return an address or a reference of a local variable?

The return statement should not return a pointer that has the address of a local variable ( sum ) because, as soon as the function exits, all local variables are destroyed and your pointer will be pointing to someplace in the memory that you no longer own.

Is it safe to delete Nullptr?

No! The C++ language guarantees that delete p will do nothing if p is equal to NULL. Since you might get the test backwards, and since most testing methodologies force you to explicitly test every branch point, you should not put in the redundant if test.