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annotate lib/fflush.c @ 16201:8250f2777afc

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maint: update all copyright year number ranges Run "make update-copyright".
author Jim Meyering <meyering@redhat.com>
date Sun, 01 Jan 2012 10:04:58 +0100
parents 20a2699b8a90
children 1d4824d7f352
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8657
05f21166eb81 * lib/stdio_.h [REPLACE_FFLUSH]: Declare rpl_fflush.
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1 /* fflush.c -- allow flushing input streams
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2 Copyright (C) 2007-2012 Free Software Foundation, Inc.
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3
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4 This program is free software: you can redistribute it and/or modify
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5 it under the terms of the GNU General Public License as published by
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6 the Free Software Foundation; either version 3 of the License, or
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7 (at your option) any later version.
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8
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9 This program is distributed in the hope that it will be useful,
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10 but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 GNU General Public License for more details.
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13
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14 You should have received a copy of the GNU General Public License
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15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
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16
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17 /* Written by Eric Blake. */
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18
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19 #include <config.h>
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20
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21 /* Specification. */
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22 #include <stdio.h>
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23
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24 #include <errno.h>
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25 #include <unistd.h>
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26
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27 #include "freading.h"
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28
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29 #include "stdio-impl.h"
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30
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31 #undef fflush
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32
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33
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34 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
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35
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36 /* Clear the stream's ungetc buffer, preserving the value of ftello (fp). */
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37 static inline void
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38 clear_ungetc_buffer_preserving_position (FILE *fp)
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39 {
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40 if (fp->_flags & _IO_IN_BACKUP)
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41 /* _IO_free_backup_area is a bit complicated. Simply call fseek. */
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42 fseeko (fp, 0, SEEK_CUR);
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43 }
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44
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45 #else
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46
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47 /* Clear the stream's ungetc buffer. May modify the value of ftello (fp). */
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48 static inline void
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49 clear_ungetc_buffer (FILE *fp)
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50 {
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51 # if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
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52 if (HASUB (fp))
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53 {
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54 fp_->_p += fp_->_r;
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55 fp_->_r = 0;
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56 }
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57 # elif defined __EMX__ /* emx+gcc */
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58 if (fp->_ungetc_count > 0)
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59 {
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60 fp->_ungetc_count = 0;
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61 fp->_rcount = - fp->_rcount;
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62 }
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63 # elif defined _IOERR /* Minix, AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, NonStop Kernel */
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64 /* Nothing to do. */
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65 # else /* other implementations */
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66 fseeko (fp, 0, SEEK_CUR);
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67 # endif
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68 }
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69
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70 #endif
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71
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72 #if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
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73
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74 static inline int
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75 disable_seek_optimization (FILE *fp)
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76 {
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77 int saved_flags = fp_->_flags & (__SOPT | __SNPT);
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78 fp_->_flags = (fp_->_flags & ~__SOPT) | __SNPT;
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79 return saved_flags;
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80 }
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81
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82 static inline void
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83 restore_seek_optimization (FILE *fp, int saved_flags)
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84 {
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85 fp_->_flags = (fp_->_flags & ~(__SOPT | __SNPT)) | saved_flags;
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86 }
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87
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88 #endif
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89
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90 static inline void
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91 update_fpos_cache (FILE *fp, off_t pos)
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92 {
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93 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
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94 # if defined __CYGWIN__
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95 /* fp_->_offset is typed as an integer. */
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96 fp_->_offset = pos;
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97 # else
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98 /* fp_->_offset is an fpos_t. */
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99 /* Use a union, since on NetBSD, the compilation flags determine
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100 whether fpos_t is typedef'd to off_t or a struct containing a
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101 single off_t member. */
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102 union
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103 {
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104 fpos_t f;
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105 off_t o;
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106 } u;
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107 u.o = pos;
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108 fp_->_offset = u.f;
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109 # endif
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110 fp_->_flags |= __SOFF;
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111 #endif
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112 }
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113
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114 /* Flush all pending data on STREAM according to POSIX rules. Both
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115 output and seekable input streams are supported. */
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116 int
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117 rpl_fflush (FILE *stream)
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118 {
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119 /* When stream is NULL, POSIX and C99 only require flushing of "output
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120 streams and update streams in which the most recent operation was not
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121 input", and all implementations do this.
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122
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123 When stream is "an output stream or an update stream in which the most
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124 recent operation was not input", POSIX and C99 requires that fflush
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125 writes out any buffered data, and all implementations do this.
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126
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127 When stream is, however, an input stream or an update stream in
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128 which the most recent operation was input, C99 specifies nothing,
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129 and POSIX only specifies behavior if the stream is seekable.
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130 mingw, in particular, drops the input buffer, leaving the file
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131 descriptor positioned at the end of the input buffer. I.e. ftell
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132 (stream) is lost. We don't want to call the implementation's
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133 fflush in this case.
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134
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135 We test ! freading (stream) here, rather than fwriting (stream), because
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136 what we need to know is whether the stream holds a "read buffer", and on
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137 mingw this is indicated by _IOREAD, regardless of _IOWRT. */
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138 if (stream == NULL || ! freading (stream))
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139 return fflush (stream);
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140
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141 #if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
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142
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143 clear_ungetc_buffer_preserving_position (stream);
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144
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145 return fflush (stream);
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146
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147 #else
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148 {
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149 /* Notes about the file-position indicator:
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150 1) The file position indicator is incremented by fgetc() and decremented
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151 by ungetc():
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152 <http://www.opengroup.org/susv3/functions/fgetc.html>
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153 "... the fgetc() function shall ... advance the associated file
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154 position indicator for the stream ..."
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155 <http://www.opengroup.org/susv3/functions/ungetc.html>
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156 "The file-position indicator is decremented by each successful
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157 call to ungetc()..."
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158 2) <http://www.opengroup.org/susv3/functions/ungetc.html> says:
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159 "The value of the file-position indicator for the stream after
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160 reading or discarding all pushed-back bytes shall be the same
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161 as it was before the bytes were pushed back."
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162 Here we are discarding all pushed-back bytes. But more specifically,
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163 3) <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> says:
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164 "[After fflush(),] the file offset of the underlying open file
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165 description shall be set to the file position of the stream, and
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166 any characters pushed back onto the stream by ungetc() ... shall
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167 be discarded." */
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168
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169 /* POSIX does not specify fflush behavior for non-seekable input
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170 streams. Some implementations purge unread data, some return
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171 EBADF, some do nothing. */
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172 off_t pos = ftello (stream);
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173 if (pos == -1)
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174 {
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175 errno = EBADF;
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176 return EOF;
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177 }
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178
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179 /* Clear the ungetc buffer. */
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180 clear_ungetc_buffer (stream);
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181
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182 /* To get here, we must be flushing a seekable input stream, so the
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183 semantics of fpurge are now appropriate to clear the buffer. To
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184 avoid losing data, the lseek is also necessary. */
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185 {
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186 int result = fpurge (stream);
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187 if (result != 0)
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188 return result;
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189 }
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190
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191 # if (defined __sferror || defined __DragonFly__) && defined __SNPT /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
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192
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193 {
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194 /* Disable seek optimization for the next fseeko call. This tells the
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195 following fseeko call to seek to the desired position directly, rather
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196 than to seek to a block-aligned boundary. */
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197 int saved_flags = disable_seek_optimization (stream);
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198 int result = fseeko (stream, pos, SEEK_SET);
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199
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200 restore_seek_optimization (stream, saved_flags);
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201 return result;
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202 }
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203
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204 # else
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205
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206 pos = lseek (fileno (stream), pos, SEEK_SET);
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207 if (pos == -1)
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208 return EOF;
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209 /* After a successful lseek, update the file descriptor's position cache
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210 in the stream. */
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211 update_fpos_cache (stream, pos);
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212
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213 return 0;
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214
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215 # endif
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216 }
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217 #endif
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218 }