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<title>realloc</title>
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<h2 align=center>realloc</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
realloc - resize allocated memory

<h3>Library</h3>
Standard C Library (libc, -lc)

<h3>Synopsis</h3>
#include &lt;stdlib.h&gt;<br>
<br>
void *<br>
realloc(void *<em>ptr</em>, size_t <em>newsize</em>);

<h3>Description</h3>

realloc 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. The size of NULL is treated as 0. Any newly allocated
space has undefined contents; the contents of existing space not
discarded by shrinkage are preserved.
<p>

<em>ptr</em> 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>
realloc returns a pointer to the resized memory block. This may not be
the same pointer as <em>ptr</em> if for internal reasons it is
necessary to move the memory block. If such a move takes place, the
old block is invalidated and <em>ptr</em> becomes invalid.
<p>

If the resize operation cannot be performed, NULL is returned, in
which case the original block pointed to by <em>ptr</em> is untouched
and remains valid.
<p>

<h3>See Also</h3>
<A HREF=calloc.html>calloc</A>,
<A HREF=malloc.html>malloc</A>,
<A HREF=free.html>free</A>

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