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  14 .TH FOPEN 3C "Nov 06, 2013"
  15 .SH NAME
  16 fopen \- open a stream
  17 .SH SYNOPSIS
  18 .LP
  19 .nf
  20 #include <stdio.h>
  21 
  22 \fBFILE *\fR\fBfopen\fR(\fBconst char *\fR\fIfilename\fR, \fBconst char *\fR\fImode\fR);
  23 .fi
  24 
  25 .SH DESCRIPTION
  26 .sp
  27 .LP
  28 The \fBfopen()\fR function opens the file whose pathname is the string pointed
  29 to by \fIfilename\fR, and associates a stream with it.
  30 .sp
  31 .LP
  32 The argument \fImode\fR points to a string beginning with one of the following
  33 base sequences:
  34 .sp
  35 .ne 2
  36 .na
  37 \fB\fBr\fR\fR
  38 .ad
  39 .RS 20n
  40 Open file for reading.
  41 .RE
  42 
  43 .sp
  44 .ne 2
  45 .na
  46 \fB\fBw\fR\fR
  47 .ad
  48 .RS 20n
  49 Truncate to  zero  length or create file for writing.
  50 .RE
  51 
  52 .sp
  53 .ne 2
  54 .na
  55 \fB\fBa\fR\fR
  56 .ad
  57 .RS 20n
  58 Append; open or create file for writing at end-of-file.
  59 .RE
  60 
  61 .sp
  62 .ne 2
  63 .na
  64 \fB\fBr+\fR\fR
  65 .ad
  66 .RS 20n
  67 Open file for update (reading and writing).
  68 .RE
  69 
  70 .sp
  71 .ne 2
  72 .na
  73 \fB\fBw+\fR\fR
  74 .ad
  75 .RS 20n
  76 Truncate to zero length or create file for update.
  77 .RE
  78 
  79 .sp
  80 .ne 2
  81 .na
  82 \fB\fBa+\fR\fR
  83 .ad
  84 .RS 20n
  85 Append; open or create file for update, writing at end-of-file.
  86 .RE
  87 
  88 .sp
  89 .LP
  90 In addition to the base sequences for the \fImode\fR argument above,
  91 three additional flags are supported via the \fBb\fR character, the
  92 \fBe\fR character, and the \fBx\fR character.  Order of these additional
  93 flags (including the \fB+\fR) does not matter.
  94 .sp
  95 .LP
  96 The character \fBb\fR has no effect, but is allowed for ISO C standard
  97 conformance (see \fBstandards\fR(5)). Opening a file with read mode (\fBr\fR as
  98 the first character in the \fImode\fR argument) fails if the file does not
  99 exist or cannot be read.
 100 .sp
 101 .LP
 102 The character \fBe\fR will cause the underlying file descriptor to be
 103 opened with the O_CLOEXEC flag as described in \fBopen\fR(2).
 104 .sp
 105 .LP
 106 The character \fBx\fR will attempt to open the specified file
 107 exclusively. This is the same behavior as opening the underlying file
 108 with the O_EXCL flag as described in \fBopen\fR(2).
 109 .sp
 110 .LP
 111 Opening a file with append mode (\fBa\fR as the first character in the
 112 \fImode\fR argument) causes all subsequent writes to the file to be forced to
 113 the then current end-of-file, regardless of intervening calls to
 114 \fBfseek\fR(3C). If two separate processes open the same file for append, each
 115 process may write freely to the file without fear of destroying output being
 116 written by the other.  The output from the two processes will be intermixed in
 117 the file in the order in which it is written.
 118 .sp
 119 .LP
 120 When a file is opened with update mode (\fB+\fR as the second or third
 121 character in the \fImode\fR argument), both input and output may be performed
 122 on the associated stream. However, output must not be directly followed by
 123 input without an intervening call to \fBfflush\fR(3C) or to a file positioning
 124 function ( \fBfseek\fR(3C), \fBfsetpos\fR(3C) or \fBrewind\fR(3C)), and input
 125 must not be directly followed by output without an intervening call to a file
 126 positioning function, unless the input operation encounters end-of-file.
 127 .sp
 128 .LP
 129 When opened, a stream is fully buffered if and only if it can be determined not
 130 to refer to an interactive device. The error and end-of-file indicators for the
 131 stream are cleared.
 132 .sp
 133 .LP
 134 If \fImode\fR begins with \fIw\fR or \fBa\fR and the file did not previously
 135 exist, upon successful completion, \fBfopen()\fR function will mark for update
 136 the \fBst_atime\fR, \fBst_ctime\fR and \fBst_mtime\fR fields of the file and
 137 the \fBst_ctime\fR and \fBst_mtime\fR fields of the parent directory.
 138 .sp
 139 .LP
 140 If \fImode\fR begins with \fIw\fR and the file did previously exist, upon
 141 successful completion, \fBfopen()\fR will mark for update the \fBst_ctime\fR
 142 and \fBst_mtime\fR fields of the file.  The \fBfopen()\fR function will
 143 allocate a file descriptor as \fBopen\fR(2) does.
 144 .sp
 145 .LP
 146 Normally, 32-bit applications return an \fBEMFILE\fR error when attempting to
 147 associate a stream with a file accessed by a file descriptor with a value
 148 greater than 255. If the last character of \fImode\fR is \fBF\fR, 32-bit
 149 applications will be allowed to associate a stream with a file accessed by a
 150 file descriptor with a value greater than 255. A \fBFILE\fR pointer obtained in
 151 this way must never be used by any code that might directly access fields in
 152 the \fBFILE\fR structure. If the fields in the \fBFILE\fR structure are used
 153 directly by 32-bit applications when the last character of mode is \fBF\fR,
 154 data corruption could occur. See the USAGE section of this manual page and the
 155 \fBenable_extended_FILE_stdio\fR(3C) manual page for other options for enabling
 156 the extended FILE facility.
 157 .sp
 158 .LP
 159 In 64-bit applications, the last character of \fImode\fR is silently ignored if
 160 it is \fBF\fR.  64-bit applications are always allowed to associate a stream
 161 with a file accessed by a file descriptor with any value.
 162 .sp
 163 .LP
 164 The largest value that can be represented correctly in an object of type
 165 \fBoff_t\fR will be established as the offset maximum in the open file
 166 description.
 167 .SH RETURN VALUES
 168 .sp
 169 .LP
 170 Upon successful completion, \fBfopen()\fR returns a pointer to the object
 171 controlling the stream.  Otherwise, a null pointer is returned and \fBerrno\fR
 172 is set to indicate the error.
 173 .sp
 174 .LP
 175 The \fBfopen()\fR function may fail and not set \fBerrno\fR if there are no
 176 free \fBstdio\fR streams.
 177 .SH ERRORS
 178 .sp
 179 .LP
 180 The \fBfopen()\fR function will fail if:
 181 .sp
 182 .ne 2
 183 .na
 184 \fB\fBEACCES\fR\fR
 185 .ad
 186 .RS 16n
 187 Search permission is denied on a component of the path prefix, or the file
 188 exists and the permissions specified by \fImode\fR are denied, or the file does
 189 not exist and write permission is denied for the parent directory of the file
 190 to be created.
 191 .RE
 192 
 193 .sp
 194 .ne 2
 195 .na
 196 \fB\fBEINTR\fR\fR
 197 .ad
 198 .RS 16n
 199 A signal was caught during the execution of \fBfopen()\fR.
 200 .RE
 201 
 202 .sp
 203 .ne 2
 204 .na
 205 \fB\fBEISDIR\fR\fR
 206 .ad
 207 .RS 16n
 208 The named file is a directory and \fImode\fR requires write access.
 209 .RE
 210 
 211 .sp
 212 .ne 2
 213 .na
 214 \fB\fBELOOP\fR\fR
 215 .ad
 216 .RS 16n
 217 Too many symbolic links were encountered in resolving \fIpath\fR.
 218 .RE
 219 
 220 .sp
 221 .ne 2
 222 .na
 223 \fB\fBEMFILE\fR\fR
 224 .ad
 225 .RS 16n
 226 There are {\fBOPEN_MAX\fR} file descriptors currently open in the calling
 227 process.
 228 .RE
 229 
 230 .sp
 231 .ne 2
 232 .na
 233 \fB\fBENAMETOOLONG\fR\fR
 234 .ad
 235 .RS 16n
 236 The length of the \fIfilename\fR exceeds \fIPATH_MAX\fR or a pathname component
 237 is longer than \fINAME_MAX\fR.
 238 .RE
 239 
 240 .sp
 241 .ne 2
 242 .na
 243 \fB\fBENFILE\fR\fR
 244 .ad
 245 .RS 16n
 246 The maximum allowable number of files is currently open in the system.
 247 .RE
 248 
 249 .sp
 250 .ne 2
 251 .na
 252 \fB\fBENOENT\fR\fR
 253 .ad
 254 .RS 16n
 255 A component of \fIfilename\fR does not name an existing file or \fIfilename\fR
 256 is an empty string.
 257 .RE
 258 
 259 .sp
 260 .ne 2
 261 .na
 262 \fB\fBENOSPC\fR\fR
 263 .ad
 264 .RS 16n
 265 The directory or file system that would contain the new file cannot be
 266 expanded, the file does not exist, and it was to be created.
 267 .RE
 268 
 269 .sp
 270 .ne 2
 271 .na
 272 \fB\fBENOTDIR\fR\fR
 273 .ad
 274 .RS 16n
 275 A component of the path prefix is not a directory.
 276 .RE
 277 
 278 .sp
 279 .ne 2
 280 .na
 281 \fB\fBENXIO\fR\fR
 282 .ad
 283 .RS 16n
 284 The named file is a character special or block special file, and the device
 285 associated with this special file does not exist.
 286 .RE
 287 
 288 .sp
 289 .ne 2
 290 .na
 291 \fB\fBEOVERFLOW\fR\fR
 292 .ad
 293 .RS 16n
 294 The current value of the file position cannot be represented correctly in an
 295 object of type \fBfpos_t\fR.
 296 .RE
 297 
 298 .sp
 299 .ne 2
 300 .na
 301 \fB\fBEROFS\fR\fR
 302 .ad
 303 .RS 16n
 304 The named file resides on a read-only file system and \fImode\fR requires write
 305 access.
 306 .RE
 307 
 308 .sp
 309 .LP
 310 The \fBfopen()\fR function may fail if:
 311 .sp
 312 .ne 2
 313 .na
 314 \fB\fBEINVAL\fR\fR
 315 .ad
 316 .RS 16n
 317 The value of the \fImode\fR argument is not valid.
 318 .RE
 319 
 320 .sp
 321 .ne 2
 322 .na
 323 \fB\fBEMFILE\fR\fR
 324 .ad
 325 .RS 16n
 326 {\fBFOPEN_MAX\fR} streams are currently open in the calling process.
 327 .sp
 328 {\fBSTREAM_MAX\fR} streams are currently open in the calling process.
 329 .RE
 330 
 331 .sp
 332 .ne 2
 333 .na
 334 \fB\fBENAMETOOLONG\fR\fR
 335 .ad
 336 .RS 16n
 337 Pathname resolution of a symbolic link produced an intermediate result whose
 338 length exceeds {\fBPATH_MAX\fR}.
 339 .RE
 340 
 341 .sp
 342 .ne 2
 343 .na
 344 \fB\fBENOMEM\fR\fR
 345 .ad
 346 .RS 16n
 347 Insufficient storage space is available.
 348 .RE
 349 
 350 .sp
 351 .ne 2
 352 .na
 353 \fB\fBETXTBSY\fR\fR
 354 .ad
 355 .RS 16n
 356 The file is a pure procedure (shared text) file that is being executed and
 357 \fImode\fR requires write access.
 358 .RE
 359 
 360 .SH USAGE
 361 .sp
 362 .LP
 363 A process is allowed to have at least {\fBFOPEN_MAX\fR} \fBstdio\fR streams
 364 open at a time. For 32-bit applications, however, the underlying ABIs formerly
 365 required that no file descriptor used to access the file underlying a
 366 \fBstdio\fR stream have a value greater than 255. To maintain binary
 367 compatibility with earlier Solaris releases, this limit still constrains 32-bit
 368 applications. However, when a 32-bit application is aware that no code that has
 369 access to the \fBFILE\fR pointer returned by \fBfopen()\fR will use the
 370 \fBFILE\fR pointer to directly access any fields in the \fBFILE\fR structure,
 371 the \fBF\fR character can be used as the last character in the \fImode\fR
 372 argument to circumvent this limit. Because it could lead to data corruption,
 373 the \fBF\fR character in \fImode\fR must never be used when the \fBFILE\fR
 374 pointer might later be used by binary code unknown to the user. The \fBF\fR
 375 character in \fImode\fR is intended to be used by library functions that need a
 376 \fBFILE\fR pointer to access data to process a user request, but do not need to
 377 pass the \fBFILE\fR pointer back to the user. 32-bit applications that have
 378 been inspected can use the extended FILE facility to circumvent this limit if
 379 the inspection shows that no \fBFILE\fR pointers will be used to directly
 380 access \fBFILE\fR structure contents.
 381 .sp
 382 .LP
 383 The \fBfopen()\fR function has a transitional interface for 64-bit file
 384 offsets.  See \fBlf64\fR(5).
 385 .SH ATTRIBUTES
 386 .sp
 387 .LP
 388 See \fBattributes\fR(5) for descriptions of the following attributes:
 389 .sp
 390 
 391 .sp
 392 .TS
 393 box;
 394 c | c
 395 l | l .
 396 ATTRIBUTE TYPE  ATTRIBUTE VALUE
 397 _
 398 Interface Stability     See below.
 399 _
 400 MT-Level        MT-Safe
 401 .TE
 402 
 403 .sp
 404 .LP
 405 The \fBF\fR character in the \fImode\fR argument is Evolving. In all other
 406 respects this function is Standard.
 407 .SH SEE ALSO
 408 .sp
 409 .LP
 410 \fBenable_extended_FILE_stdio\fR(3C), \fBfclose\fR(3C), \fBfdopen\fR(3C),
 411 \fBfflush\fR(3C), \fBfreopen\fR(3C), \fBfsetpos\fR(3C), \fBrewind\fR(3C),
 412 \fBopen\fR(2), \fBattributes\fR(5), \fBlf64\fR(5), \fBstandards\fR(5)