voidpointer

A void pointer, written as void*, is a pointer type used in C and C++ that can hold the address of any object but does not have a specified data type. Because it has no type, a void* cannot be dereferenced directly or used in pointer arithmetic without first converting to a pointer to a concrete type.

In C, a void* acts as a generic object pointer. It can hold addresses of objects of any type, and you can assign between object pointers and void* without an explicit cast in either direction. To access the pointed-to data, you must cast the void* back to a pointer of the appropriate type. Pointer arithmetic is not allowed on void* in standard C; you typically cast to a char* or to the target type before performing arithmetic. Dereferencing a void* requires casting to the correct type first.

In C++, void* is also used as a generic pointer, but conversions between void* and other object pointer types are not implicit and require explicit casts (such as static_cast or reinterpret_cast). Dereferencing still requires casting to a concrete type, and misuse can lead to undefined behavior.

Common uses of void* include implementing generic data structures and APIs, such as buffers, opaque handles, and wrappers around memory allocation functions (for example, malloc in C returns void*). They enable type-agnostic interfaces but at the cost of type safety and potential runtime errors if the actual type is misidentified or miscast.

Limitations and pitfalls include the risk of incorrect casts, alignment issues, and violations of object lifetimes or aliasing rules. Modern code often minimizes void* usage by using typed wrappers or generic constructs where available.

Example: void* p = malloc(sizeof(int)); *(int*)p = 42; free(p);