libio/vsnprintf.c

   1 /* Copyright (C) 1994-2020 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include "libioP.h"
  28 #include "strfile.h"
  29
  30 static int _IO_strn_overflow (FILE *fp, int c) __THROW;
  31
  32 static int
  33 _IO_strn_overflow (FILE *fp, int c)
  34 {
  35   /* When we come to here this means the user supplied buffer is
  36      filled.  But since we must return the number of characters which
  37      would have been written in total we must provide a buffer for
  38      further use.  We can do this by writing on and on in the overflow
  39      buffer in the _IO_strnfile structure.  */
  40   _IO_strnfile *snf = (_IO_strnfile *) fp;
  41
  42   if (fp->_IO_buf_base != snf->overflow_buf)
  43     {
  44       /* Terminate the string.  We know that there is room for at
  45          least one more character since we initialized the stream with
  46          a size to make this possible.  */
  47       *fp->_IO_write_ptr = '\0';
  48
  49       _IO_setb (fp, snf->overflow_buf,
  50                 snf->overflow_buf + sizeof (snf->overflow_buf), 0);
  51
  52       fp->_IO_write_base = snf->overflow_buf;
  53       fp->_IO_read_base = snf->overflow_buf;
  54       fp->_IO_read_ptr = snf->overflow_buf;
  55       fp->_IO_read_end = snf->overflow_buf + sizeof (snf->overflow_buf);
  56     }
  57
  58   fp->_IO_write_ptr = snf->overflow_buf;
  59   fp->_IO_write_end = snf->overflow_buf;
  60
  61   /* Since we are not really interested in storing the characters
  62      which do not fit in the buffer we simply ignore it.  */
  63   return c;
  64 }
  65
  66
  67 const struct _IO_jump_t _IO_strn_jumps libio_vtable attribute_hidden =
  68 {
  69   JUMP_INIT_DUMMY,
  70   JUMP_INIT(finish, _IO_str_finish),
  71   JUMP_INIT(overflow, _IO_strn_overflow),
  72   JUMP_INIT(underflow, _IO_str_underflow),
  73   JUMP_INIT(uflow, _IO_default_uflow),
  74   JUMP_INIT(pbackfail, _IO_str_pbackfail),
  75   JUMP_INIT(xsputn, _IO_default_xsputn),
  76   JUMP_INIT(xsgetn, _IO_default_xsgetn),
  77   JUMP_INIT(seekoff, _IO_str_seekoff),
  78   JUMP_INIT(seekpos, _IO_default_seekpos),
  79   JUMP_INIT(setbuf, _IO_default_setbuf),
  80   JUMP_INIT(sync, _IO_default_sync),
  81   JUMP_INIT(doallocate, _IO_default_doallocate),
  82   JUMP_INIT(read, _IO_default_read),
  83   JUMP_INIT(write, _IO_default_write),
  84   JUMP_INIT(seek, _IO_default_seek),
  85   JUMP_INIT(close, _IO_default_close),
  86   JUMP_INIT(stat, _IO_default_stat),
  87   JUMP_INIT(showmanyc, _IO_default_showmanyc),
  88   JUMP_INIT(imbue, _IO_default_imbue)
  89 };
  90
  91
  92 int
  93 __vsnprintf_internal (char *string, size_t maxlen, const char *format,
  94                       va_list args, unsigned int mode_flags)
  95 {
  96   _IO_strnfile sf;
  97   int ret;
  98 #ifdef _IO_MTSAFE_IO
  99   sf.f._sbf._f._lock = NULL;
 100 #endif
 101
 102   /* We need to handle the special case where MAXLEN is 0.  Use the
 103      overflow buffer right from the start.  */
 104   if (maxlen == 0)
 105     {
 106       string = sf.overflow_buf;
 107       maxlen = sizeof (sf.overflow_buf);
 108     }
 109
 110   _IO_no_init (&sf.f._sbf._f, _IO_USER_LOCK, -1, NULL, NULL);
 111   _IO_JUMPS (&sf.f._sbf) = &_IO_strn_jumps;
 112   string[0] = '\0';
 113   _IO_str_init_static_internal (&sf.f, string, maxlen - 1, string);
 114   ret = __vfprintf_internal (&sf.f._sbf._f, format, args, mode_flags);
 115
 116   if (sf.f._sbf._f._IO_buf_base != sf.overflow_buf)
 117     *sf.f._sbf._f._IO_write_ptr = '\0';
 118   return ret;
 119 }
 120
 121 int
 122 ___vsnprintf (char *string, size_t maxlen, const char *format, va_list args)
 123 {
 124   return __vsnprintf_internal (string, maxlen, format, args, 0);
 125 }
 126 ldbl_weak_alias (___vsnprintf, __vsnprintf)
 127 ldbl_weak_alias (___vsnprintf, vsnprintf)