home | help 
REALLOCARRAY(3) 	     Library Functions Manual		 REALLOCARRAY(3)

NAME
     reallocarray -- memory reallocation function

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

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

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

RETURN VALUES
     The  reallocarray() function returns a pointer to the allocated space; oth-
     erwise, 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.   Bet-
     ter 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 FreeBSD 11.0.

FreeBSD 11.1			   May 1, 2015			 REALLOCARRAY(3)
home | help