nuttx/libs/libc/stdio/lib_vasprintf.c

/****************************************************************************
 * libs/libc/stdio/lib_vasprintf.c
 *
 *   Copyright (C) 2011-2012 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * 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 NuttX 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT OWNER 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.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>

#include "libc.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: vasprintf
 *
 * Description:
 *   This function is similar to vsprintf, except that it dynamically
 *   allocates a string (as with malloc) to hold the output, instead of
 *   putting the output in a buffer you allocate in advance.  The ptr
 *   argument should be the address of a char * object, and a successful
 *   call to vasprintf stores a pointer to the newly allocated string at that
 *   location.
 *
 * Returned Value:
 *   The returned value is the number of characters allocated for the buffer,
 *   or less than zero if an error occurred. Usually this means that the
 *   buffer could not be allocated.
 *
 ****************************************************************************/

int vasprintf(FAR char **ptr, FAR const IPTR char *fmt, va_list ap)
{
  struct lib_outstream_s nulloutstream;
  struct lib_memoutstream_s memoutstream;

  /* On some architectures, va_list is really a pointer to a structure on
   * the stack. And the va_arg builtin will modify that instance of va_list.
   * Since vasprintf traverse the parameters in the va_list twice, the
   * va_list will be altered in this first cases and the second usage will
   * fail. This is a known issue with x86_64.
   */

#ifdef va_copy
  va_list ap2;
#endif
  FAR char *buf;
  int nbytes;

  DEBUGASSERT(ptr && fmt);

#ifdef va_copy
  va_copy(ap2, ap);
#endif

  /* First, use a nullstream to get the size of the buffer.  The number
   * of bytes returned may or may not include the null terminator.
   */

  lib_nulloutstream(&nulloutstream);
  lib_vsprintf((FAR struct lib_outstream_s *)&nulloutstream, fmt, ap);

  /* Then allocate a buffer to hold that number of characters, adding one
   * for the null terminator.
   */

  buf = (FAR char *)lib_malloc(nulloutstream.nput + 1);
  if (!buf)
    {
      va_end(ap);
#ifdef va_copy
      va_end(ap2);
#endif
      return ERROR;
    }

  /* Initialize a memory stream to write into the allocated buffer.  The
   * memory stream will reserve one byte at the end of the buffer for the
   * null terminator and will not report this in the number of output bytes.
   */

  lib_memoutstream((FAR struct lib_memoutstream_s *)&memoutstream,
                   buf, nulloutstream.nput + 1);

  /* Then let lib_vsprintf do it's real thing */

#ifdef va_copy
  nbytes = lib_vsprintf((FAR struct lib_outstream_s *)&memoutstream.public,
                        fmt, ap2);
  va_end(ap2);
#else
  nbytes = lib_vsprintf((FAR struct lib_outstream_s *)&memoutstream.public,
                        fmt, ap);
#endif

  va_end(ap);

  /* Return a pointer to the string to the caller.  NOTE: the memstream put()
   * method has already added the NUL terminator to the end of the string
   * (not included in the nput count).
   *
   * Hmmm.. looks like the memory would be stranded if lib_vsprintf()
   * returned an error.  Does that ever happen?
   */

  DEBUGASSERT(nbytes < 0 || nbytes == nulloutstream.nput);
  *ptr = buf;
  return nbytes;
}