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In C++, while the NULL macro was inherited from C, the integer literal for zero has been traditionally preferred to represent a null pointer constant. [9] However, C++11 introduced the explicit null pointer constant nullptr and type nullptr_t to be used instead, providing a type safe null pointer.
A null pointer has a value reserved for indicating that the pointer does not refer to a valid object. Null pointers are routinely used to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
A null Animal* pointer is possible, and could be useful as a place-holder, but may not be used for direct dispatch: a->MakeSound() is undefined behavior if a is a null pointer. The null object pattern solves this problem by providing a special NullAnimal class which can be instantiated bound to an Animal pointer or reference.
Two common uses of the assert macro are to assert that a pointer is not null and to ensure that an array index is in-bounds. [5] Below is a program using the assert macro. This program will always evaluate pointer as false, as pointer is a null pointer and does not point to a valid memory location:
C, C++ — — — — — Formerly PRQA QA·C and QA·C++, deep static analysis of C/C++ for quality assurance and guideline/coding standard enforcement with MISRA support. Infer Static Analyzer: 2024-06-21 (1.2.0) Yes; MIT — C, C++, Objective-C Java — — — — Targets null pointer problems, leaks, concurrency issues and API usage for ...
Unlike static_cast and C-style typecast (where type check occurs while compiling), a type safety check is performed at runtime. If the types are not compatible, an exception will be thrown (when dealing with references ) or a null pointer will be returned (when dealing with pointers ).
In C and C++, 0 represents the null pointer. As with Boolean values, the C standard library includes a macro definition NULL whose use is encouraged. Other languages provide a specific null or nil value and when this is the case no alternative should be used. The typed pointer constant nullptr has been introduced with C++11.
To expose dangling pointer errors, one common programming technique is to set pointers to the null pointer or to an invalid address once the storage they point to has been released. When the null pointer is dereferenced (in most languages) the program will immediately terminate—there is no potential for data corruption or unpredictable behavior.