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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.
When a dangling pointer is used after it has been freed without allocating a new chunk of memory to it, this becomes known as a "use after free" vulnerability. [4] For example, CVE - 2014-1776 is a use-after-free vulnerability in Microsoft Internet Explorer 6 through 11 [ 5 ] being used by zero-day attacks by an advanced persistent threat .
C supports the use of pointers, a type of reference that records the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a ...
A function pointer, also called a subroutine pointer or procedure pointer, is a pointer referencing executable code, rather than data. Dereferencing the function pointer yields the referenced function, which can be invoked and passed arguments just as in a normal function call.
Because pointers store a memory location's address, instead of a value directly, inappropriate use of pointers can lead to undefined behavior in a program, particularly due to dangling pointers or wild pointers. Smart pointers are opaque data structures that act like pointers but can only be accessed through particular methods.
Use a minimum of two runtime assertions per function. Restrict the scope of data to the smallest possible. Check the return value of all non-void functions, or cast to void to indicate the return value is useless. Use the preprocessor sparingly. Limit pointer use to a single dereference, and do not use function pointers.
On many common platforms, this use of pointer punning can create problems if different pointers are aligned in machine-specific ways. Furthermore, pointers of different sizes can alias accesses to the same memory, causing problems that are unchecked by the compiler. Even when data size and pointer representation match, however, compilers can ...
In the C programming language, struct is the keyword used to define a composite, a.k.a. record, data type – a named set of values that occupy a block of memory. It allows for the different values to be accessed via a single identifier, often a pointer.