<!-- Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013 The President and Fellows of Harvard College. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. Neither the name of the University nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. --> <html> <head> <title>realloc</title> <body bgcolor=#ffffff> <h2 align=center>realloc</h2> <h4 align=center>OS/161 Reference Manual</h4> <h3>Name</h3> <p> realloc - resize allocated memory </p> <h3>Library</h3> <p> Standard C Library (libc, -lc) </p> <h3>Synopsis</h3> <p> <tt>#include <stdlib.h></tt><br> <br> <tt>void *</tt><br> <tt>realloc(void *</tt><em>ptr</em><tt>, size_t </tt><em>newsize</em><tt>);</tt> </p> <h3>Description</h3> <p> <tt>realloc</tt> attempts to change the size of the memory block pointed to by <em>ptr</em> to <em>newsize</em>, causing the block to shrink or grow as necessary. If the size cannot be changed, a new block is allocated and the contents (up to the lesser of the previous size and <em>newsize</em>) are copied, then the old block is freed. </p> <p> The size of <tt>NULL</tt> is treated as 0. If the size is increased, any newly allocated space has undefined contents. If the size is decreased, the space discarded may no longer be accessed. Otherwise the contents of the memory block are preserved. </p> <p> <em>ptr</em> must be NULL or have been previously returned by <A HREF=malloc.html>malloc</A>, <A HREF=calloc.html>calloc</A>, or realloc. </p> The alignment and other restrictions described for <A HREF=malloc.html>malloc</A> apply equally to realloc. <p> <h3>Return Values</h3> <p> <tt>realloc</tt> returns a pointer to the resized memory block. This may not be the same pointer as <em>ptr</em>. If so, the old block is invalidated and <em>ptr</em> becomes invalid. </p> <p> If the operation cannot be performed at all, NULL is returned and the original block pointed to by <em>ptr</em> is untouched and remains valid. </p> <h3>See Also</h3> <p> <A HREF=calloc.html>calloc</A>, <A HREF=malloc.html>malloc</A>, <A HREF=free.html>free</A> </p> </body> </html>