1.\" $OpenBSD: stdio.3,v 1.17 2004/06/20 21:09:30 jfb 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 April 19, 1994 31.Dt STDIO 3 32.Os 33.Sh NAME 34.Nm stdio 35.Nd standard input/output library functions 36.Sh SYNOPSIS 37.Fd #include <stdio.h> 38.Pp 39.Fd FILE *stdin; 40.Fd FILE *stdout; 41.Fd FILE *stderr; 42.Sh DESCRIPTION 43The standard 44.Tn I/O 45library provides a simple and efficient buffered stream 46.Tn I/O 47interface. 48Input and output is mapped into logical data streams and the physical 49.Tn I/O 50characteristics are concealed. 51The functions and macros are listed below; 52more information is available from the individual man pages. 53.Pp 54A stream is associated with an external file (which may be a physical 55device) by 56.Dq opening 57a file, which may involve creating a new file. 58Creating an existing file causes its former contents to be discarded. 59If a file can support positioning requests (such as a disk file, as opposed 60to a terminal) then a 61.Dq file position indicator 62associated with the stream is positioned at the start of the file (byte 63zero), unless the file is opened with append mode. 64If append mode 65is used, the position indicator will be placed at the end-of-file. 66The position indicator is maintained by subsequent reads, writes 67and positioning requests. 68All input occurs as if the characters 69were read by successive calls to the 70.Xr fgetc 3 71function; all output takes place as if all characters were 72written by successive calls to the 73.Xr fputc 3 74function. 75.Pp 76A file is disassociated from a stream by 77.Dq closing 78it. 79Output streams are flushed (any unwritten buffer contents are transferred 80to the host environment) before the stream is disassociated from the file. 81The value of a pointer to a 82.Dv FILE 83object is indeterminate (garbage) after a file is closed. 84.Pp 85A file may be subsequently reopened, by the same or another program 86execution, and its contents reclaimed or modified (if it can be repositioned 87at the start). 88If the main function returns to its original caller, or the 89.Xr exit 3 90function is called, all open files are closed (hence all output 91streams are flushed) before program termination. 92Other methods of program termination may not close files properly and hence 93buffered output may be lost. 94In particular, 95.Xr _exit 2 96does not flush stdio files. 97Neither does an exit due to a signal. 98Buffers are flushed by 99.Xr abort 3 100as required by POSIX, although previous implementations did not. 101.Pp 102This implementation needs and makes 103no distinction between 104.Dq text 105and 106.Dq binary 107streams. 108In effect, all streams are binary. 109No translation is performed and no extra padding appears on any stream. 110.Pp 111At program startup, three streams are predefined and need not be 112opened explicitly: 113.Pp 114.Bl -bullet -compact -offset indent 115.It 116.Em standard input 117(for reading conventional input), 118.It 119.Em standard output 120(for writing conventional output), and 121.It 122.Em standard error 123(for writing diagnostic output). 124.El 125.Pp 126These streams are abbreviated 127.Em stdin , 128.Em stdout , 129and 130.Em stderr . 131Initially, the standard error stream 132is unbuffered; the standard input and output streams are 133fully buffered if and only if the streams do not refer to 134an interactive or 135.Dq terminal 136device, as determined by the 137.Xr isatty 3 138function. 139In fact, 140.Em all 141freshly opened streams that refer to terminal devices 142default to line buffering, and 143pending output to such streams is written automatically 144whenever such an input stream is read. 145Note that this applies only to 146.Dq "true reads" ; 147if the read request can be satisfied by existing buffered data, 148no automatic flush will occur. 149In these cases, 150or when a large amount of computation is done after printing 151part of a line on an output terminal, it is necessary to 152.Xr fflush 3 153the standard output before going off and computing so that the output 154will appear. 155Alternatively, these defaults may be modified via the 156.Xr setvbuf 3 157function. 158.Pp 159The 160.Nm stdio 161library is a part of the library 162.Xr libc 163and routines are automatically loaded as needed by the compiler. 164The 165.Tn SYNOPSIS 166sections of the following manual pages indicate which include files 167are to be used, what the compiler declaration for the function 168looks like and which external variables are of interest. 169.Pp 170The following are defined as macros; 171these names may not be re-used 172without first removing their current definitions with 173.Dv #undef : 174.Dv BUFSIZ , 175.Dv EOF , 176.Dv FILENAME_MAX , 177.Dv FOPEN_MAX , 178.Dv L_cuserid , 179.Dv L_ctermid , 180.Dv L_tmpnam , 181.Dv NULL , 182.Dv SEEK_END , 183.Dv SEEK_SET , 184.Dv SEE_CUR , 185.Dv TMP_MAX , 186.Dv clearerr , 187.Dv feof , 188.Dv ferror , 189.Dv fileno , 190.Dv freopen , 191.Dv fwopen , 192.Dv getc , 193.Dv getchar , 194.Dv putc , 195.Dv putchar , 196.Dv stderr , 197.Dv stdin , 198.Dv stdout . 199Function versions of the macro functions 200.Xr feof , 201.Xr ferror , 202.Xr clearerr , 203.Xr fileno , 204.Xr getc , 205.Xr getchar , 206.Xr putc , 207and 208.Xr putchar 209exist and will be used if the macro 210definitions are explicitly removed. 211.Sh LIST OF FUNCTIONS 212.Bl -column "Description" 213.Sy Function Description 214asprintf formatted output conversion with allocation 215clearerr check and reset stream status 216fclose close a stream 217fdopen stream open functions 218feof check and reset stream status 219ferror check and reset stream status 220fflush flush a stream 221fgetc get next character or word from input stream 222fgetln get a line from a stream 223fgetpos reposition a stream 224fgets get a line from a stream 225fileno get a stream's underlying file descriptor 226fopen stream open functions 227fprintf formatted output conversion 228fpurge flush a stream 229fputc output a character or word to a stream 230fputs output a line to a stream 231fread binary stream input/output 232freopen stream open functions 233fropen open a stream 234fscanf input format conversion 235fseek reposition a stream 236fsetpos reposition a stream 237ftell reposition a stream 238funopen open a stream 239fwopen open a stream 240fwrite binary stream input/output 241getc get next character or word from input stream 242getchar get next character or word from input stream 243gets get a line from a stream 244getw get next character or word from input stream 245mkstemp create unique temporary file 246mktemp create unique temporary file 247perror system error messages 248printf formatted output conversion 249putc output a character or word to a stream 250putchar output a character or word to a stream 251puts output a line to a stream 252putw output a character or word to a stream 253remove remove directory entry 254rewind reposition a stream 255scanf input format conversion 256setbuf stream buffering operations 257setbuffer stream buffering operations 258setlinebuf stream buffering operations 259setvbuf stream buffering operations 260snprintf formatted output conversion 261sprintf formatted output conversion 262sscanf input format conversion 263strerror system error messages 264sys_errlist system error messages 265sys_nerr system error messages 266tempnam temporary file routines 267tmpfile temporary file routines 268tmpnam temporary file routines 269ungetc un-get character from input stream 270vasprintf formatted output conversion with allocation 271vfprintf formatted output conversion 272vfscanf input format conversion 273vprintf formatted output conversion 274vscanf input format conversion 275vsnprintf formatted output conversion 276vsprintf formatted output conversion 277vsscanf input format conversion 278.El 279.Sh SEE ALSO 280.Xr close 2 , 281.Xr open 2 , 282.Xr read 2 , 283.Xr write 2 284.Sh STANDARDS 285The 286.Nm stdio 287library conforms to 288.St -ansiC . 289.Sh BUGS 290The standard buffered functions do not interact well with certain other 291library and system functions, especially 292.Xr vfork 293and 294.Xr abort . 295