reallocptr

Reallocptr is a programming utility concept used in C-like environments to resize a block of dynamically allocated memory and update the caller’s pointer in place. The primary goal is to avoid forgetting to assign the result of a reallocation back to the original pointer, which can lead to leaks or dangling references.

Typical usage and signatures

A reallocptr helper is commonly implemented as a function or macro that takes a pointer to a pointer (void ** or T **) and a new size. A representative form is reallocptr(void **pp, size_t new_size). The function calls realloc on the block pointed to by *pp and, if successful, writes the new address back to *pp. It usually returns a status indicator (such as 0 for success or nonzero for failure) or leaves *pp unchanged on failure. A macro variant might capture the same behavior with a compact pattern, for example by performing a temporary assignment of the result and updating the caller’s pointer only if the allocation succeeds.

Behavior and guarantees

The core guarantee is that, on success, the caller’s original pointer is updated to point at the reallocated block. On failure, the behavior depends on the implementation: the original pointer is typically left unchanged, and an error code or boolean failure is returned. Implementations must handle NULL pointers gracefully (realloc(NULL, n) behaves like malloc(n)) and should define behavior when new_size is zero (which may free memory and set the pointer to NULL in some environments).

Considerations and caveats

Reallocptr abstracts away the boilerplate of checking realloc’s result but still requires careful error handling and awareness of ownership. It does not automatically copy contents beyond the old size beyond what realloc performs, and differences in allocation behavior across platforms (especially for zero sizes) should be documented. It is not part of the C standard; many projects implement their own version to enforce in-place pointer updates and consistent error reporting.