Updated: 2022/Sep/29

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REALLOCARRAY(3)            Library Functions Manual            REALLOCARRAY(3)

NAME
     reallocarray - reallocate memory for an array of elements checking for
     overflow

SYNOPSIS
     #include <stdlib.h>

     void *
     reallocarray(void *ptr, size_t nmemb, size_t size);

DESCRIPTION
     The reallocarray() function reallocates the pointer ptr to a size
     appropriate to handle an allocation of nmemb elements in an array where
     each of the array elements is size bytes using realloc(3) and making sure
     that overflow does not happen in the multiplication of "nmemb * size".
     Otherwise it behaves like realloc(3).

RETURN VALUES
     The reallocarray() function will return NULL if there was overflow or if
     realloc(3) failed setting errno to ENOMEM or preserving the value from
     realloc(3).

SEE ALSO
     malloc(3), realloc(3), reallocarr(3)

HISTORY
     The reallocarray() function first appeared in OpenBSD 5.6.
     reallocarray() was redesigned in NetBSD 8 as reallocarr(3).  Until
     NetBSD 10, reallocarray was available in the _OPENBSD_SOURCE namespace.

CAVEATS
     The reallocarray() function was designed to facilitate safe, robust
     programming and overcome the shortcomings of the malloc(3) and realloc(3)
     functions by centralizing the overflow check in the multiplication of
     nmemb and size.

     There are still portability issues.  (It does not solve the 0 sized
     allocation return ambiguity in the C standard: does reallocarray() return
     NULL or a unique pointer to memory that cannot be accessed?  Does a NULL
     mean that an error occurred, and can someone check errno in that case to
     find out what happened?)  For this reason NetBSD decided to go with an
     alternative implementation, and created reallocarr(3).

NetBSD 10.99                   September 9, 2022                  NetBSD 10.99