stdio/stdio.3

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  32 .\"     @(#)stdio.3     8.7 (Berkeley) 4/19/94
  33 .\" $FreeBSD: src/lib/libc/stdio/stdio.3,v 1.26 2004/07/02 23:52:12 ru Exp $
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  35 .Dd January 10, 2003
  36 .Dt STDIO 3
  37 .Os
  38 .Sh NAME
  39 .Nm stdio
  40 .Nd standard input/output library functions
  41 .Sh LIBRARY
  42 .Lb libc
  43 .Sh SYNOPSIS
  44 .In stdio.h
  45 .Vt FILE *stdin ;
  46 .Vt FILE *stdout ;
  47 .Vt FILE *stderr ;
  48 .Pp
  49 Note:
  50 The current implementation does not allow these variables
  51 to be evaluated at C compile/link time.
  52 That is, a runtime calculation must be performed, such as:
  53 .Bd -literal -offset indent
  54 #include <stdio.h>
  55
  56 static FILE *var;
  57
  58 int main() {
  59     var = stdout;
  60 }
  61 .Ed
  62 .Sh DESCRIPTION
  63 The standard
  64 .Tn I/O
  65 library provides a simple and efficient buffered stream
  66 .Tn I/O
  67 interface.
  68 Input and output is mapped into logical data streams
  69 and the physical
  70 .Tn I/O
  71 characteristics are concealed.
  72 The functions and macros are listed
  73 below; more information is available from the individual man pages.
  74 .Pp
  75 A stream is associated with an external file (which may be a physical
  76 device) by
  77 .Em opening
  78 a file, which may involve creating a new file.
  79 Creating an
  80 existing file causes its former contents to be discarded.
  81 If a file can support positioning requests (such as a disk file, as opposed
  82 to a terminal) then a
  83 .Em file position indicator
  84 associated with the stream is positioned at the start of the file (byte
  85 zero), unless the file is opened with append mode.
  86 If append mode
  87 is used, the position indicator will be placed at the end-of-file.
  88 The position indicator is maintained by subsequent reads, writes
  89 and positioning requests.
  90 All input occurs as if the characters
  91 were read by successive calls to the
  92 .Xr fgetc 3
  93 function; all output takes place as if all characters were
  94 written by successive calls to the
  95 .Xr fputc 3
  96 function.
  97 .Pp
  98 A file is disassociated from a stream by
  99 .Em closing
 100 the file.
 101 Output streams are flushed (any unwritten buffer contents are transferred
 102 to the host environment) before the stream is disassociated from the file.
 103 The value of a pointer to a
 104 .Dv FILE
 105 object is indeterminate (garbage) after a file is closed.
 106 .Pp
 107 A file may be subsequently reopened, by the same or another program
 108 execution, and its contents reclaimed or modified (if it can be repositioned
 109 at the start).
 110 If the main function returns to its original caller, or
 111 the
 112 .Xr exit 3
 113 function is called, all open files are closed (hence all output
 114 streams are flushed) before program termination.
 115 Other methods
 116 of program termination may not close files properly and hence
 117 buffered output may be lost.
 118 In particular,
 119 .Xr _exit 2
 120 does not flush stdio files.
 121 Neither does an exit due to a signal.
 122 Buffers are flushed by
 123 .Xr abort 3
 124 as required by POSIX, although previous implementations did not.
 125 .Pp
 126 This implementation makes no distinction between
 127 .Dq text
 128 and
 129 .Dq binary
 130 streams.
 131 In effect, all streams are binary.
 132 No translation is performed and no extra padding appears on any stream.
 133 .Pp
 134 At program startup, three streams are predefined and need not be
 135 opened explicitly:
 136 .Bl -bullet -compact -offset indent
 137 .It
 138 .Em standard input
 139 (for reading conventional input),
 140 .It
 141 .Em standard output
 142 (for writing conventional output), and
 143 .It
 144 .Em standard error
 145 (for writing diagnostic output).
 146 .El
 147 These streams are abbreviated
 148 .Dv stdin , stdout
 149 and
 150 .Dv stderr .
 151 Initially, the standard error stream
 152 is unbuffered; the standard input and output streams are
 153 fully buffered if and only if the streams do not refer to
 154 an interactive or
 155 .Dq terminal
 156 device, as determined by the
 157 .Xr isatty 3
 158 function.
 159 In fact,
 160 .Em all
 161 freshly-opened streams that refer to terminal devices
 162 default to line buffering, and
 163 pending output to such streams is written automatically
 164 whenever such an input stream is read.
 165 Note that this applies only to
 166 .Dq "true reads" ;
 167 if the read request can be satisfied by existing buffered data,
 168 no automatic flush will occur.
 169 In these cases,
 170 or when a large amount of computation is done after printing
 171 part of a line on an output terminal, it is necessary to
 172 .Xr fflush 3
 173 the standard output before going off and computing so that the output
 174 will appear.
 175 Alternatively, these defaults may be modified via the
 176 .Xr setvbuf 3
 177 function.
 178 .Pp
 179 The
 180 .Nm
 181 library is a part of the library
 182 .Nm libc
 183 and routines are automatically loaded as needed by the C compiler.
 184 The
 185 .Tn SYNOPSIS
 186 sections of the following manual pages indicate which include files
 187 are to be used, what the compiler declaration for the function
 188 looks like and which external variables are of interest.
 189 .Pp
 190 The following are defined as macros;
 191 these names may not be re-used
 192 without first removing their current definitions with
 193 .Ic #undef :
 194 .Dv BUFSIZ ,
 195 .Dv EOF ,
 196 .Dv FILENAME_MAX ,
 197 .Dv FOPEN_MAX ,
 198 .Dv L_ctermid ,
 199 .Dv L_cuserid ,
 200 .Dv L_tmpnam ,
 201 .Dv NULL ,
 202 .Dv P_tmpdir ,
 203 .Dv SEEK_CUR ,
 204 .Dv SEEK_END ,
 205 .Dv SEEK_SET ,
 206 .Dv TMP_MAX ,
 207 .Dv clearerr ,
 208 .Dv clearerr_unlocked ,
 209 .Dv feof ,
 210 .Dv feof_unlocked ,
 211 .Dv ferror ,
 212 .Dv ferror_unlocked ,
 213 .Dv fileno ,
 214 .Dv fileno_unlocked ,
 215 .Dv fropen ,
 216 .Dv fwopen ,
 217 .Dv getc ,
 218 .Dv getc_unlocked ,
 219 .Dv getchar ,
 220 .Dv getchar_unlocked ,
 221 .Dv putc ,
 222 .Dv putc_unlocked ,
 223 .Dv putchar ,
 224 .Dv putchar_unlocked ,
 225 .Dv stderr ,
 226 .Dv stdin
 227 and
 228 .Dv stdout .
 229 Function versions of the macro functions
 230 .Dv clearerr ,
 231 .Dv clearerr_unlocked ,
 232 .Dv feof ,
 233 .Dv feof_unlocked ,
 234 .Dv ferror ,
 235 .Dv ferror_unlocked ,
 236 .Dv fileno ,
 237 .Dv fileno_unlocked ,
 238 .Dv getc ,
 239 .Dv getc_unlocked ,
 240 .Dv getchar ,
 241 .Dv getchar_unlocked ,
 242 .Dv putc ,
 243 .Dv putc_unlocked ,
 244 .Dv putchar ,
 245 and
 246 .Dv putchar_unlocked
 247 exist and will be used if the macro
 248 definitions are explicitly removed.
 249 .Sh LEGACY SYNOPSIS
 250 The -D_NONSTD_SOURCE flag can be used
 251 to allow stdin, stdout, and/or stderr
 252 to be evaluated at compile/link time, as:
 253 .Bd -literal -offset indent
 254 #include <stdio.h>
 255
 256 static FILE *var = stdout;
 257 .Ed
 258 .Sh SEE ALSO
 259 .Xr close 2 ,
 260 .Xr open 2 ,
 261 .Xr read 2 ,
 262 .Xr write 2 ,
 263 .Xr compat 5
 264 .Sh BUGS
 265 The standard buffered functions do not interact well with certain other
 266 library and system functions, especially
 267 .Xr vfork 2 .
 268 .Sh STANDARDS
 269 The
 270 .Nm
 271 library conforms to
 272 .St -isoC-99 .
 273 .Sh LIST OF FUNCTIONS
 274 .Bl -column "Description"
 275 .It Sy "Function        Description"
 276 .It "asprintf   formatted output conversion"
 277 .It ""
 278 .It "clearerr   check and reset stream status"
 279 .It ""
 280 .It "fclose     close a stream"
 281 .It "fdopen     stream open functions"
 282 .It "feof       check and reset stream status"
 283 .It "ferror     check and reset stream status"
 284 .It "fflush     flush a stream"
 285 .It "fgetc      get next character or word from input stream"
 286 .It "fgetln     get a line from a stream"
 287 .It "fgetpos    reposition a stream"
 288 .It "fgets      get a line from a stream"
 289 .It "fgetwc     get next wide character from input stream"
 290 .It "fgetws     get a line of wide characters from a stream"
 291 .It "fileno     check and reset stream status"
 292 .It "fopen      stream open functions"
 293 .It "fprintf    formatted output conversion"
 294 .It "fpurge     flush a stream"
 295 .It "fputc      output a character or word to a stream"
 296 .It "fputs      output a line to a stream"
 297 .It "fputwc     output a wide character to a stream"
 298 .It "fputws     output a line of wide characters to a stream"
 299 .It "fread      binary stream input/output"
 300 .It "freopen    stream open functions"
 301 .It "fropen     open a stream"
 302 .It "fscanf     input format conversion"
 303 .It "fseek      reposition a stream"
 304 .It "fsetpos    reposition a stream"
 305 .It "ftell      reposition a stream"
 306 .It "funopen    open a stream"
 307 .It "fwide      set/get orientation of stream"
 308 .It "fwopen     open a stream"
 309 .It "fwprintf   formatted wide character output conversion"
 310 .It "fwrite     binary stream input/output"
 311 .It ""
 312 .It "getc       get next character or word from input stream"
 313 .It "getchar    get next character or word from input stream"
 314 .It "gets       get a line from a stream"
 315 .It "getw       get next character or word from input stream"
 316 .It "getwc      get next wide character from input stream"
 317 .It "getwchar   get next wide character from input stream"
 318 .It ""
 319 .It "mkdtemp    create unique temporary directory"
 320 .It "mkstemp    create unique temporary file"
 321 .It "mktemp     create unique temporary file"
 322 .It ""
 323 .It "perror     system error messages"
 324 .It "printf     formatted output conversion"
 325 .It "putc       output a character or word to a stream"
 326 .It "putchar    output a character or word to a stream"
 327 .It "puts       output a line to a stream"
 328 .It "putw       output a character or word to a stream"
 329 .It "putwc      output a wide character to a stream"
 330 .It "putwchar   output a wide character to a stream"
 331 .It ""
 332 .It "remove     remove directory entry"
 333 .It "rewind     reposition a stream"
 334 .It ""
 335 .It "scanf      input format conversion"
 336 .It "setbuf     stream buffering operations"
 337 .It "setbuffer  stream buffering operations"
 338 .It "setlinebuf stream buffering operations"
 339 .It "setvbuf    stream buffering operations"
 340 .It "snprintf   formatted output conversion"
 341 .It "sprintf    formatted output conversion"
 342 .It "sscanf     input format conversion"
 343 .It "strerror   system error messages"
 344 .It "swprintf   formatted wide character output conversion"
 345 .It "sys_errlist        system error messages"
 346 .It "sys_nerr   system error messages"
 347 .It ""
 348 .It "tempnam    temporary file routines"
 349 .It "tmpfile    temporary file routines"
 350 .It "tmpnam     temporary file routines"
 351 .It ""
 352 .It "ungetc     un-get character from input stream"
 353 .It "ungetwc    un-get wide character from input stream"
 354 .It ""
 355 .It "vasprintf  formatted output conversion"
 356 .It "vfprintf   formatted output conversion"
 357 .It "vfscanf    input format conversion"
 358 .It "vfwprintf  formatted wide character output conversion"
 359 .It "vprintf    formatted output conversion"
 360 .It "vscanf     input format conversion"
 361 .It "vsnprintf  formatted output conversion"
 362 .It "vsprintf   formatted output conversion"
 363 .It "vsscanf    input format conversion"
 364 .It "vswprintf  formatted wide character output conversion"
 365 .It "vwprintf   formatted wide character output conversion"
 366 .It ""
 367 .It "wprintf    formatted wide character output conversion"
 368 .El