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A null pointer is one that points to nowhere. When you dereference a pointer p, you say "give me the data at the location stored in "p". When p is a null pointer, the location stored in p is nowhere, you're saying "give me the data at the location 'nowhere'". Obviously, it can't do this, so it throws a null pointer exception.
A pointer references a location in memory, and obtaining the value at the location a pointer refers to is known as dereferencing the pointer. Dereferencing is done by applying the unary * operator on the pointer. "Dereferencing a NULL pointer" means performing *p when the p is NULL.
Sep 30, 2010 · In C NULL can be defined as 0 or as ((void *)0), C99 allows for implementation defined null pointer constants. So it actually comes down to the implementation's definition of NULL and you will have to inspect it in your standard library.
A constant expression of type int with the value 0, or an expression of this type, cast to type void * is a null pointer constant, which if converted to a pointer becomes a null pointer. It is guaranteed by the standard to compare unequal to any pointer to any object or function. NULL is a macro, defined in as a null pointer constant.
12. The only way a this pointer can be NULL is if some code in the program has exhibited undefined behaviour. It might for example be achieved by something like. void *place = nullptr; MyClass *object = new (place) MyClass (); The problem is that this effectively dereferences a NULL pointer, so has undefined behaviour.
A void pointer, (void *) is a raw pointer to some memory location. A null pointer is a special pointer that doesn't point to anything, by definition. It can be a pointer to any type, void or otherwise. A void pointer can be null or not: void *void_ptr1 = nullptr; void *void_ptr2 = malloc(42);
May 4, 2010 · My intent in this answer is supplemental to the most basic of concepts of a null pointer. This simplest definition, as listed in many places is whenever a base value pointing to an address gets assigned a '0' or NULL value because the zero page, 0th memory location is part of the operating systems address space and operating system doesn't allow access to its address space by the user's program.
NULL is not a null pointer; it is required to be defined as a "null pointer constant" (which in C++, cannot be a pointer, and in C, traditionally is not a pointer). There are three separate concepts which must be dealt with: NULL, a null pointer, and a null pointer constant. And how a null pointer is physically represented (its bit pattern) is ...
Oct 14, 2015 · The reason why is that any() returns a generic object reference. This object is unboxed to an integer, so the generic type is determined to be 'Integer'. The object is null though, so the unboxing fails accessing a null pointer. anyInt() provides a native integer, so it works. –
Aug 23, 2019 · I'm getting a Null Pointer Exception as shown in the code when I run the following Junit test. Can someone please help me fix it? import com.apexsct.pouservice.amq.inboxlistener.
