1.\" $OpenBSD: stdio.3,v 1.31 2014/07/03 06:08:06 jmc Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.Dd $Mdocdate: July 3 2014 $ 31.Dt STDIO 3 32.Os 33.Sh NAME 34.Nm stdio 35.Nd standard input/output library functions 36.Sh SYNOPSIS 37.In stdio.h 38.Pp 39.Fd FILE *stdin; 40.Fd FILE *stdout; 41.Fd FILE *stderr; 42.Sh DESCRIPTION 43The standard I/O library 44provides a simple and efficient buffered stream I/O interface. 45Input and output is mapped into logical data streams and the physical I/O 46characteristics are concealed. 47The functions and macros are listed below; 48more information is available from the individual man pages. 49.Pp 50A stream is associated with an external file (which may be a physical 51device) by 52.Dq opening 53a file, which may involve creating a new file. 54Creating an existing file causes its former contents to be discarded. 55If a file can support positioning requests (such as a disk file, as opposed 56to a terminal) then a 57.Dq file position indicator 58associated with the stream is positioned at the start of the file (byte 59zero), unless the file is opened with append mode. 60If append mode 61is used, the position indicator will be placed at the end-of-file. 62The position indicator is maintained by subsequent reads, writes, 63and positioning requests. 64All input occurs as if the characters 65were read by successive calls to the 66.Xr fgetc 3 67function; all output takes place as if all characters were 68written by successive calls to the 69.Xr fputc 3 70function. 71.Pp 72A file is disassociated from a stream by 73.Dq closing 74it. 75Output streams are flushed (any unwritten buffer contents are transferred 76to the host environment) before the stream is disassociated from the file. 77The value of a pointer to a 78.Dv FILE 79object is indeterminate (garbage) after a file is closed. 80.Pp 81A file may be subsequently reopened, by the same or another program 82execution, and its contents reclaimed or modified (if it can be repositioned 83at the start). 84If the main function returns to its original caller, or the 85.Xr exit 3 86function is called, all open files are closed (hence all output 87streams are flushed) before program termination. 88Other methods of program termination may not close files properly and hence 89buffered output may be lost. 90In particular, 91.Xr _exit 2 92does not flush 93.Nm 94files. 95Neither does an exit due to a signal. 96Buffers are flushed by 97.Xr abort 3 , 98as required by POSIX, although in previous implementations they were not. 99.Pp 100This implementation needs and makes 101no distinction between 102.Dq text 103and 104.Dq binary 105streams. 106In effect, all streams are binary. 107No translation is performed and no extra padding appears on any stream. 108.Pp 109At program startup, three streams are predefined and need not be 110opened explicitly: 111.Pp 112.Bl -bullet -compact -offset indent 113.It 114.Em standard input 115(for reading conventional input), 116.It 117.Em standard output 118(for writing conventional output), and 119.It 120.Em standard error 121(for writing diagnostic output). 122.El 123.Pp 124These streams are abbreviated 125.Em stdin , 126.Em stdout , 127and 128.Em stderr . 129Initially, the standard error stream 130is unbuffered; the standard input and output streams are 131fully buffered if and only if the streams do not refer to 132an interactive or 133.Dq terminal 134device, as determined by the 135.Xr isatty 3 136function. 137In fact, 138.Em all 139freshly opened streams that refer to terminal devices 140default to line buffering, and 141pending output to such streams is written automatically 142whenever such an input stream is read. 143Note that this applies only to 144.Dq "true reads" ; 145if the read request can be satisfied by existing buffered data, 146no automatic flush will occur. 147In these cases, 148or when a large amount of computation is done after printing 149part of a line on an output terminal, it is necessary to 150.Xr fflush 3 151the standard output so that the output will appear immediately. 152Alternatively, these defaults may be modified via the 153.Xr setvbuf 3 154function. 155.Pp 156The 157.Nm stdio 158library is a part of the library libc 159and routines are automatically loaded as needed by the compiler. 160The SYNOPSIS 161sections of the following manual pages indicate which include files 162are to be used, what the compiler declaration for the function 163looks like, and which external variables are of interest. 164.Pp 165The following are defined as macros; 166these names may not be re-used 167without first removing their current definitions with 168.Dv #undef : 169.Dv BUFSIZ , 170.Dv EOF , 171.Dv FILENAME_MAX , 172.Dv FOPEN_MAX , 173.Dv L_ctermid , 174.Dv L_tmpnam , 175.Dv NULL , 176.Dv SEEK_END , 177.Dv SEEK_SET , 178.Dv SEEK_CUR , 179.Dv TMP_MAX , 180.Dv clearerr , 181.Dv feof , 182.Dv ferror , 183.Dv fileno , 184.Dv freopen , 185.Dv fwopen , 186.Dv getc , 187.Dv getchar , 188.Dv putc , 189.Dv putchar , 190.Dv stderr , 191.Dv stdin , 192.Dv stdout . 193Function versions of the macro functions 194.Xr feof 3 , 195.Xr ferror 3 , 196.Xr clearerr 3 , 197.Xr fileno 3 , 198.Xr getc 3 , 199.Xr getchar 3 , 200.Xr putc 3 , 201and 202.Xr putchar 3 203exist and will be used if the macro 204definitions are explicitly removed. 205.Sh LIST OF FUNCTIONS 206.Bl -column "sys_errlist" "Description" 207.It Sy Function Ta Sy Description 208.It asprintf Ta "formatted output conversion with allocation" 209.It clearerr Ta "check and reset stream status" 210.It dprintf Ta "formatted output conversion" 211.It fclose Ta "close a stream" 212.It fdopen Ta "stream open functions" 213.It feof Ta "check and reset stream status" 214.It ferror Ta "check and reset stream status" 215.It fflush Ta "flush a stream" 216.It fgetc Ta "get next character or word from input stream" 217.It fgetln Ta "get a line from a stream" 218.It fgetpos Ta "reposition a stream" 219.It fgets Ta "get a line from a stream" 220.It fgetwc Ta "get next wide character from input stream" 221.It fgetws Ta "get a line of wide characters from a stream" 222.It fileno Ta "get a stream's underlying file descriptor" 223.It fopen Ta "stream open functions" 224.It fprintf Ta "formatted output conversion" 225.It fpurge Ta "flush a stream" 226.It fputc Ta "output a character or word to a stream" 227.It fputs Ta "output a line to a stream" 228.It fputwc Ta "output a wide character to a stream" 229.It fputws Ta "output a line of wide characters to a stream" 230.It fread Ta "binary stream input/output" 231.It freopen Ta "stream open functions" 232.It fropen Ta "open a stream" 233.It fscanf Ta "input format conversion" 234.It fseek Ta "reposition a stream" 235.It fsetpos Ta "reposition a stream" 236.It ftell Ta "reposition a stream" 237.It funopen Ta "open a stream" 238.It fwide Ta "set/get orientation of stream" 239.It fwopen Ta "open a stream" 240.It fwprintf Ta "formatted wide character output conversion" 241.It fwrite Ta "binary stream input/output" 242.It getc Ta "get next character or word from input stream" 243.It getchar Ta "get next character or word from input stream" 244.It getdelim Ta "read a delimited record from a stream" 245.It getline Ta "read a delimited record from a stream" 246.It getw Ta "get next character or word from input stream" 247.It getwc Ta "get next wide character from input stream" 248.It getwchar Ta "get next wide character from input stream" 249.It mkdtemp Ta "create unique temporary directory" 250.It mkstemp Ta "create unique temporary file" 251.It mktemp Ta "create unique temporary file" 252.It perror Ta "system error messages" 253.It printf Ta "formatted output conversion" 254.It putc Ta "output a character or word to a stream" 255.It putchar Ta "output a character or word to a stream" 256.It puts Ta "output a line to a stream" 257.It putw Ta "output a character or word to a stream" 258.It putwc Ta "output a wide character to a stream" 259.It putwchar Ta "output a wide character to a stream" 260.It remove Ta "remove directory entry" 261.It rewind Ta "reposition a stream" 262.It scanf Ta "input format conversion" 263.It setbuf Ta "stream buffering operations" 264.It setbuffer Ta "stream buffering operations" 265.It setlinebuf Ta "stream buffering operations" 266.It setvbuf Ta "stream buffering operations" 267.It snprintf Ta "formatted output conversion" 268.It sprintf Ta "formatted output conversion" 269.It sscanf Ta "input format conversion" 270.It strerror Ta "system error messages" 271.It swprintf Ta "formatted wide character output conversion" 272.It sys_errlist Ta "system error messages" 273.It sys_nerr Ta "system error messages" 274.It tempnam Ta "temporary file routines" 275.It tmpfile Ta "temporary file routines" 276.It tmpnam Ta "temporary file routines" 277.It ungetc Ta "un-get character from input stream" 278.It ungetwc Ta "un-get wide character from input stream" 279.It vasprintf Ta "formatted output conversion with allocation" 280.It vdprintf Ta "formatted output conversion" 281.It vfprintf Ta "formatted output conversion" 282.It vfscanf Ta "input format conversion" 283.It vfwprintf Ta "formatted wide character output conversion" 284.It vprintf Ta "formatted output conversion" 285.It vscanf Ta "input format conversion" 286.It vsnprintf Ta "formatted output conversion" 287.It vsprintf Ta "formatted output conversion" 288.It vsscanf Ta "input format conversion" 289.It vswprintf Ta "formatted wide character output conversion" 290.It vwprintf Ta "formatted wide character output conversion" 291.It wprintf Ta "formatted wide character output conversion" 292.El 293.Sh SEE ALSO 294.Xr close 2 , 295.Xr open 2 , 296.Xr read 2 , 297.Xr write 2 298.Sh STANDARDS 299The 300.Nm stdio 301library conforms to 302.St -isoC-99 . 303.Sh BUGS 304The standard buffered functions do not interact well with certain other 305library and system functions, especially 306.Xr vfork 2 307and 308.Xr abort 3 . 309