stdio/FreeBSD/stdio.3

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  28 .\"     @(#)stdio.3     8.7 (Berkeley) 4/19/94
  29 .\" $FreeBSD: src/lib/libc/stdio/stdio.3,v 1.30 2009/03/04 03:38:51 das Exp $
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  31 .Dd March 3, 2009
  32 .Dt STDIO 3
  33 .Os
  34 .Sh NAME
  35 .Nm stdio
  36 .Nd standard input/output library functions
  37 .Sh LIBRARY
  38 .Lb libc
  39 .Sh SYNOPSIS
  40 .In stdio.h
  41 .Vt FILE *stdin ;
  42 .Vt FILE *stdout ;
  43 .Vt FILE *stderr ;
  44 .Sh DESCRIPTION
  45 The standard
  46 .Tn I/O
  47 library provides a simple and efficient buffered stream
  48 .Tn I/O
  49 interface.
  50 Input and output is mapped into logical data streams
  51 and the physical
  52 .Tn I/O
  53 characteristics are concealed.
  54 The functions and macros are listed
  55 below; more information is available from the individual man pages.
  56 .Pp
  57 A stream is associated with an external file (which may be a physical
  58 device) by
  59 .Em opening
  60 a file, which may involve creating a new file.
  61 Creating an
  62 existing file causes its former contents to be discarded.
  63 If a file can support positioning requests (such as a disk file, as opposed
  64 to a terminal) then a
  65 .Em file position indicator
  66 associated with the stream is positioned at the start of the file (byte
  67 zero), unless the file is opened with append mode.
  68 If append mode
  69 is used, the position indicator will be placed at the end-of-file.
  70 The position indicator is maintained by subsequent reads, writes
  71 and positioning requests.
  72 All input occurs as if the characters
  73 were read by successive calls to the
  74 .Xr fgetc 3
  75 function; all output takes place as if all characters were
  76 written by successive calls to the
  77 .Xr fputc 3
  78 function.
  79 .Pp
  80 A file is disassociated from a stream by
  81 .Em closing
  82 the file.
  83 Output streams are flushed (any unwritten buffer contents are transferred
  84 to the host environment) before the stream is disassociated from the file.
  85 The value of a pointer to a
  86 .Dv FILE
  87 object is indeterminate (garbage) after a file is closed.
  88 .Pp
  89 A file may be subsequently reopened, by the same or another program
  90 execution, and its contents reclaimed or modified (if it can be repositioned
  91 at the start).
  92 If the main function returns to its original caller, or
  93 the
  94 .Xr exit 3
  95 function is called, all open files are closed (hence all output
  96 streams are flushed) before program termination.
  97 Other methods
  98 of program termination may not close files properly and hence
  99 buffered output may be lost.
 100 In particular,
 101 .Xr _exit 2
 102 does not flush stdio files.
 103 Neither does an exit due to a signal.
 104 Buffers are flushed by
 105 .Xr abort 3
 106 as required by POSIX, although previous implementations did not.
 107 .Pp
 108 This implementation makes no distinction between
 109 .Dq text
 110 and
 111 .Dq binary
 112 streams.
 113 In effect, all streams are binary.
 114 No translation is performed and no extra padding appears on any stream.
 115 .Pp
 116 At program startup, three streams are predefined and need not be
 117 opened explicitly:
 118 .Bl -bullet -compact -offset indent
 119 .It
 120 .Em standard input
 121 (for reading conventional input),
 122 .It
 123 .Em standard output
 124 (for writing conventional output), and
 125 .It
 126 .Em standard error
 127 (for writing diagnostic output).
 128 .El
 129 These streams are abbreviated
 130 .Dv stdin , stdout
 131 and
 132 .Dv stderr .
 133 Initially, the standard error stream
 134 is unbuffered; the standard input and output streams are
 135 fully buffered if and only if the streams do not refer to
 136 an interactive or
 137 .Dq terminal
 138 device, as determined by the
 139 .Xr isatty 3
 140 function.
 141 In fact,
 142 .Em all
 143 freshly-opened streams that refer to terminal devices
 144 default to line buffering, and
 145 pending output to such streams is written automatically
 146 whenever such an input stream is read.
 147 Note that this applies only to
 148 .Dq "true reads" ;
 149 if the read request can be satisfied by existing buffered data,
 150 no automatic flush will occur.
 151 In these cases,
 152 or when a large amount of computation is done after printing
 153 part of a line on an output terminal, it is necessary to
 154 .Xr fflush 3
 155 the standard output before going off and computing so that the output
 156 will appear.
 157 Alternatively, these defaults may be modified via the
 158 .Xr setvbuf 3
 159 function.
 160 .Pp
 161 The
 162 .Nm
 163 library is a part of the library
 164 .Nm libc
 165 and routines are automatically loaded as needed by the C compiler.
 166 The
 167 .Tn SYNOPSIS
 168 sections of the following manual pages indicate which include files
 169 are to be used, what the compiler declaration for the function
 170 looks like and which external variables are of interest.
 171 .Pp
 172 The following are defined as macros;
 173 these names may not be re-used
 174 without first removing their current definitions with
 175 .Ic #undef :
 176 .Dv BUFSIZ ,
 177 .Dv EOF ,
 178 .Dv FILENAME_MAX ,
 179 .Dv FOPEN_MAX ,
 180 .Dv L_ctermid ,
 181 .Dv L_cuserid ,
 182 .Dv L_tmpnam ,
 183 .Dv NULL ,
 184 .Dv P_tmpdir ,
 185 .Dv SEEK_CUR ,
 186 .Dv SEEK_END ,
 187 .Dv SEEK_SET ,
 188 .Dv TMP_MAX ,
 189 .Dv clearerr ,
 190 .Dv clearerr_unlocked ,
 191 .Dv feof ,
 192 .Dv feof_unlocked ,
 193 .Dv ferror ,
 194 .Dv ferror_unlocked ,
 195 .Dv fileno ,
 196 .Dv fileno_unlocked ,
 197 .Dv fropen ,
 198 .Dv fwopen ,
 199 .Dv getc ,
 200 .Dv getc_unlocked ,
 201 .Dv getchar ,
 202 .Dv getchar_unlocked ,
 203 .Dv putc ,
 204 .Dv putc_unlocked ,
 205 .Dv putchar ,
 206 .Dv putchar_unlocked ,
 207 .Dv stderr ,
 208 .Dv stdin
 209 and
 210 .Dv stdout .
 211 Function versions of the macro functions
 212 .Dv clearerr ,
 213 .Dv clearerr_unlocked ,
 214 .Dv feof ,
 215 .Dv feof_unlocked ,
 216 .Dv ferror ,
 217 .Dv ferror_unlocked ,
 218 .Dv fileno ,
 219 .Dv fileno_unlocked ,
 220 .Dv getc ,
 221 .Dv getc_unlocked ,
 222 .Dv getchar ,
 223 .Dv getchar_unlocked ,
 224 .Dv putc ,
 225 .Dv putc_unlocked ,
 226 .Dv putchar ,
 227 and
 228 .Dv putchar_unlocked
 229 exist and will be used if the macro
 230 definitions are explicitly removed.
 231 .Sh SEE ALSO
 232 .Xr close 2 ,
 233 .Xr open 2 ,
 234 .Xr read 2 ,
 235 .Xr write 2
 236 .Sh STANDARDS
 237 The
 238 .Nm
 239 library conforms to
 240 .St -isoC-99 .
 241 .Sh LIST OF FUNCTIONS
 242 .Bl -column "Description"
 243 .It Sy "Function        Description"
 244 .It "asprintf   formatted output conversion"
 245 .It "clearerr   check and reset stream status"
 246 .It "dprintf    formatted output conversion"
 247 .It "fclose     close a stream"
 248 .It "fdopen     stream open functions"
 249 .It "feof       check and reset stream status"
 250 .It "ferror     check and reset stream status"
 251 .It "fflush     flush a stream"
 252 .It "fgetc      get next character or word from input stream"
 253 .It "fgetln     get a line from a stream"
 254 .It "fgetpos    reposition a stream"
 255 .It "fgets      get a line from a stream"
 256 .It "fgetwc     get next wide character from input stream"
 257 .It "fgetws     get a line of wide characters from a stream"
 258 .It "fileno     check and reset stream status"
 259 .It "fopen      stream open functions"
 260 .It "fprintf    formatted output conversion"
 261 .It "fpurge     flush a stream"
 262 .It "fputc      output a character or word to a stream"
 263 .It "fputs      output a line to a stream"
 264 .It "fputwc     output a wide character to a stream"
 265 .It "fputws     output a line of wide characters to a stream"
 266 .It "fread      binary stream input/output"
 267 .It "freopen    stream open functions"
 268 .It "fropen     open a stream"
 269 .It "fscanf     input format conversion"
 270 .It "fseek      reposition a stream"
 271 .It "fsetpos    reposition a stream"
 272 .It "ftell      reposition a stream"
 273 .It "funopen    open a stream"
 274 .It "fwide      set/get orientation of stream"
 275 .It "fwopen     open a stream"
 276 .It "fwprintf   formatted wide character output conversion"
 277 .It "fwrite     binary stream input/output"
 278 .It "getc       get next character or word from input stream"
 279 .It "getchar    get next character or word from input stream"
 280 .It "getdelim   get a line from a stream"
 281 .It "getline    get a line from a stream"
 282 .It "gets       get a line from a stream"
 283 .It "getw       get next character or word from input stream"
 284 .It "getwc      get next wide character from input stream"
 285 .It "getwchar   get next wide character from input stream"
 286 .It "mkdtemp    create unique temporary directory"
 287 .It "mkstemp    create unique temporary file"
 288 .It "mktemp     create unique temporary file"
 289 .It "perror     system error messages"
 290 .It "printf     formatted output conversion"
 291 .It "putc       output a character or word to a stream"
 292 .It "putchar    output a character or word to a stream"
 293 .It "puts       output a line to a stream"
 294 .It "putw       output a character or word to a stream"
 295 .It "putwc      output a wide character to a stream"
 296 .It "putwchar   output a wide character to a stream"
 297 .It "remove     remove directory entry"
 298 .It "rewind     reposition a stream"
 299 .It "scanf      input format conversion"
 300 .It "setbuf     stream buffering operations"
 301 .It "setbuffer  stream buffering operations"
 302 .It "setlinebuf stream buffering operations"
 303 .It "setvbuf    stream buffering operations"
 304 .It "snprintf   formatted output conversion"
 305 .It "sprintf    formatted output conversion"
 306 .It "sscanf     input format conversion"
 307 .It "strerror   system error messages"
 308 .It "swprintf   formatted wide character output conversion"
 309 .It "sys_errlist        system error messages"
 310 .It "sys_nerr   system error messages"
 311 .It "tempnam    temporary file routines"
 312 .It "tmpfile    temporary file routines"
 313 .It "tmpnam     temporary file routines"
 314 .It "ungetc     un-get character from input stream"
 315 .It "ungetwc    un-get wide character from input stream"
 316 .It "vasprintf  formatted output conversion"
 317 .It "vdprintf   formatted output conversion"
 318 .It "vfprintf   formatted output conversion"
 319 .It "vfscanf    input format conversion"
 320 .It "vfwprintf  formatted wide character output conversion"
 321 .It "vprintf    formatted output conversion"
 322 .It "vscanf     input format conversion"
 323 .It "vsnprintf  formatted output conversion"
 324 .It "vsprintf   formatted output conversion"
 325 .It "vsscanf    input format conversion"
 326 .It "vswprintf  formatted wide character output conversion"
 327 .It "vwprintf   formatted wide character output conversion"
 328 .It "wprintf    formatted wide character output conversion"
 329 .El
 330 .Sh BUGS
 331 The standard buffered functions do not interact well with certain other
 332 library and system functions, especially
 333 .Xr vfork 2 .