DragonFly On-Line Manual Pages

REALLOCARRAY(3)       DragonFly Library Functions Manual       REALLOCARRAY(3)

NAME
     reallocarray, recallocarray -- memory reallocation functions

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

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

     void *
     recallocarray(void *ptr, size_t oldnmemb, size_t nmemb, size_t size);

DESCRIPTION
     The reallocarray() function is similar to the realloc() function except
     it operates on number members of size size and checks for integer
     overflow in the calculation number * size.

     The recallocarray() function is similar to reallocarray() except it
     ensures newly allocated memory is cleared similar to calloc().

RETURN VALUES
     The reallocarray() function returns a pointer to the allocated space;
     otherwise, a NULL pointer is returned and errno is set to ENOMEM.

EXAMPLES
     Consider reallocarray() when there is multiplication in the size argument
     of malloc() or realloc().  For example, avoid this common idiom as it may
     lead to integer overflow:

           if ((p = malloc(num * size)) == NULL)
                   err(1, "malloc");

     A drop-in replacement is the OpenBSD extension reallocarray():

           if ((p = reallocarray(NULL, num, size)) == NULL)
                   err(1, "reallocarray");

     When using realloc(), be careful to avoid the following idiom:

           size += 50;
           if ((p = realloc(p, size)) == NULL)
                   return (NULL);

     Do not adjust the variable describing how much memory has been allocated
     until the allocation has been successful.  This can cause aberrant
     program behavior if the incorrect size value is used.  In most cases, the
     above sample will also result in a leak of memory.  As stated earlier, a
     return value of NULL indicates that the old object still remains
     allocated.  Better code looks like this:

           newsize = size + 50;
           if ((newp = realloc(p, newsize)) == NULL) {
                   free(p);
                   p = NULL;
                   size = 0;
                   return (NULL);
           }
           p = newp;
           size = newsize;

     As with malloc(), it is important to ensure the new size value will not
     overflow; i.e. avoid allocations like the following:

           if ((newp = realloc(p, num * size)) == NULL) {
                   ...

     Instead, use reallocarray():

           if ((newp = reallocarray(p, num, size)) == NULL) {
                   ...

SEE ALSO
     realloc(3)

HISTORY
     The reallocarray() function first appeared in OpenBSD 5.6 and
     DragonFly 5.5.

     The recallocarray() function appeared in OpenBSD 6.1 and DragonFly 5.5.

DragonFly 5.5                   April 11, 2019                   DragonFly 5.5