asprintf() does use realloc() internally, but saying so in the manpage can be

misinterpreted to mean that the pointer passed to asprintf() must be suitable
for passing to realloc() as-is (ie. either a NULL pointer or a valid pointer).

lib/libc/stdio/printf.3

@@ -34,7 +34,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     @(#)printf.3	8.1 (Berkeley) 6/4/93
-.\"     $Id$
+.\"     $Id: printf.3,v 1.11 1999/07/12 20:47:33 nik Exp $
 .\"
 .Dd June 4, 1993
 .Dt PRINTF 3
@@ -103,9 +103,7 @@ and
 and
 .Fn vasprintf
 dynamically allocate a new string with
-.Xr malloc 3
-/
-.Xr realloc 3 .
+.Xr malloc 3 .
 .Pp
 These functions write the output under the control of a
 .Fa format