1.\" $NetBSD: stdio.3,v 1.26 2015/09/06 04:20:50 mrg 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.\" @(#)stdio.3 8.7 (Berkeley) 4/19/94 31.\" 32.Dd September 6, 2015 33.Dt STDIO 3 34.Os 35.Sh NAME 36.Nm stdio 37.Nd standard input/output library functions 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdio.h 42.Vt FILE *stdin; 43.Vt FILE *stdout; 44.Vt FILE *stderr; 45.Sh DESCRIPTION 46The standard 47.Tn I/O 48library provides a simple and efficient buffered stream 49.Tn I/O 50interface. 51Input and output is mapped into logical data streams 52and the physical 53.Tn I/O 54characteristics are concealed. 55.Pp 56A stream is associated with an external file (which may be a physical 57device) by 58.Em opening 59a file, which may involve creating a new file. 60Creating an existing file causes its former contents to be discarded. 61If a file can support positioning requests (such as a disk file, as opposed 62to a terminal) then a 63.Em file position indicator 64associated with the stream is positioned at the start of the file (byte 65zero), unless the file is opened with append mode. 66If append mode 67is used, the position indicator will be placed the end-of-file. 68The position indicator is maintained by subsequent reads, writes 69and positioning requests. 70All input occurs as if the characters 71were read by successive calls to the 72.Xr fgetc 3 73function; all output takes place as if all characters were 74read by successive calls to the 75.Xr fputc 3 76function. 77.Pp 78A file is disassociated from a stream by 79.Em closing 80the file. 81Output streams are flushed (any unwritten buffer contents are transferred 82to the host environment) before the stream is disassociated from the file. 83The value of a pointer to a 84.Dv FILE 85object is indeterminate after a file is closed (garbage). 86.Pp 87A file may be subsequently reopened, by the same or another program 88execution, and its contents reclaimed or modified (if it can be repositioned 89at the start). 90If the main function returns to its original caller, or the 91.Xr exit 3 92function is called, all open files are closed (hence all output 93streams are flushed) before program termination. 94Other methods of program termination, such as 95.Xr abort 3 96do not bother about closing files properly. 97.Pp 98This implementation needs and makes 99no distinction between 100.Dq text 101and 102.Dq binary 103streams. 104In effect, all streams are binary. 105No translation is performed and no extra padding appears on any stream. 106.Pp 107At program startup, three streams are predefined and need not be 108opened explicitly: 109.Bl -enum -offset indent 110.It 111.Em standard input 112for reading conventional input, 113.It 114.Em standard output 115for writing conventional output, and 116.It 117.Em standard error 118for writing diagnostic output. 119.El 120.Pp 121These streams are abbreviated 122.Em stdin , 123.Em stdout , 124and 125.Em stderr . 126.Pp 127Initially, the standard error stream 128is unbuffered; the standard input and output streams are 129fully buffered if and only if the streams do not refer to 130an interactive or 131.Dq terminal 132device, as determined by the 133.Xr isatty 3 134function. 135In fact, 136.Em all 137freshly-opened streams that refer to terminal devices 138default to line buffering, and 139pending output to such streams is written automatically 140whenever an such an input stream is read. 141Note that this applies only to 142.Dq "true reads" ; 143if the read request can be satisfied by existing buffered data, 144no automatic flush will occur. 145In these cases, 146or when a large amount of computation is done after printing 147part of a line on an output terminal, it is necessary to 148.Xr fflush 3 149the standard output before going off and computing so that the output 150will appear. 151Alternatively, these defaults may be modified via the 152.Xr setvbuf 3 153function. 154.Sh IMPLEMENTATION NOTES 155In multi-threaded applications, operations on streams perform implicit 156locking, except for the 157.Fn getc_unlocked , 158.Fn getchar_unlocked , 159.Fn putc_unlocked , 160and 161.Fn putchar_unlocked 162functions. 163Explicit control of stream locking is available through the 164.Fn flockfile , 165.Fn ftrylockfile , 166and 167.Fn funlockfile 168functions . 169.Pp 170The following are defined as macros; these names may not be re-used 171without first removing their current definitions with 172.Dv #undef : 173.Dv BUFSIZ , 174.Dv EOF , 175.Dv FILENAME_MAX , 176.Dv FOPEN_MAX , 177.Dv L_cuserid , 178.Dv L_ctermid , 179.Dv L_tmpnam , 180.Dv NULL , 181.Dv SEEK_END , 182.Dv SEEK_SET , 183.Dv SEE_CUR , 184.Dv TMP_MAX , 185.Fn clearerr , 186.Fn feof , 187.Fn ferror , 188.Fn fileno , 189.Fn freopen , 190.Fn fwopen , 191.Fn getc , 192.Fn getc_unlocked , 193.Fn getchar , 194.Fn getchar_unlocked , 195.Fn putc , 196.Fn putc_unlocked , 197.Fn putchar , 198.Fn putchar_unlocked , 199.Dv stderr , 200.Dv stdin , 201.Dv stdout . 202.Pp 203Function versions of the macro functions 204.Fn feof , 205.Fn ferror , 206.Fn clearerr , 207.Fn fileno , 208.Fn getc , 209.Fn getc_unlocked , 210.Fn getchar , 211.Fn getchar_unlocked , 212.Fn putc , 213.Fn putc_unlocked , 214.Fn putchar , 215and 216.Fn putchar_unlocked 217exist and will be used if the macros definitions are explicitly removed. 218.Sh SEE ALSO 219.Xr close 2 , 220.Xr open 2 , 221.Xr read 2 , 222.Xr write 2 223.Sh STANDARDS 224The 225.Nm 226library conforms to 227.St -ansiC . 228.Sh LIST OF FUNCTIONS 229.Bl -column "putchar_unlocked" "Description" 230.It Sy Function Description 231.It asprintf formatted output conversion with allocation 232.It asprintf_l formatted output conversion with allocation 233.It clearerr check and reset stream status 234.It dprintf formatted output conversion 235.It dprintf_l formatted output conversion 236.It fclose close a stream 237.It fdopen stream open functions 238.It feof check and reset stream status 239.It ferror check and reset stream status 240.It fflush flush a stream 241.It fgetc get next character or word from input stream 242.It fgetln get a line from a stream 243.It fgetpos reposition a stream 244.It fgets get a line from a stream 245.It fgetwc get next wide character from input stream 246.It fileno check and reset stream status 247.It flockfile lock a stream 248.It fmemopen open a stream that points to a memory buffer 249.It fopen stream open functions 250.It fprintf formatted output conversion 251.It fprintf_l formatted output conversion 252.It fpurge flush a stream 253.It fputc output a character or word to a stream 254.It fputs output a line to a stream 255.It fputwc output a wide character to a stream 256.It fread binary stream input/output 257.It freopen stream open functions 258.It fropen open a stream 259.It fscanf input format conversion 260.It fscanf_l input format conversion 261.It fseek reposition a stream 262.It fseeko reposition a stream 263.It fsetpos reposition a stream 264.It ftell reposition a stream 265.It ftello reposition a stream 266.It ftrylockfile lock a stream (non-blocking) 267.It funlockfile unlock a stream 268.It funopen open a stream 269.It funopen2 open a stream, with flush support 270.It fwide set/get orientation of a stream 271.It fwopen open a stream 272.It fwrite binary stream input/output 273.It getc get next character or word from input stream 274.It getc_unlocked get next character or word from input stream 275.It Ta (no implicit locking) 276.It getchar get next character or word from input stream 277.It getchar_unlocked get next character or word from input stream 278.It Ta (no implicit locking) 279.It getdelim get a delimited record from a stream 280.It getline get a line from a stream 281.It gets get a line from a stream 282.It getw get next character or word from input stream 283.It getwc get next wide character from input stream 284.It getwchar get next wide character from input stream 285.It mkstemp create unique temporary file 286.It mktemp create unique temporary file 287.It open_memstream open memory as a stream 288.It popen open a program as a stream 289.It popenve open a program as a stream 290.It pclose close an opened program stream 291.It perror system error messages 292.It printf formatted output conversion 293.It printf_l formatted output conversion 294.It putc output a character or word to a stream 295.It putc_unlocked output a character or word to a stream 296.It Ta (no implicit locking) 297.It putchar output a character or word to a stream 298.It putchar_unlocked output a character or word to a stream 299.It Ta (no implicit locking) 300.It puts output a line to a stream 301.It putw output a character or word to a stream 302.It putwc output a wide character to a stream 303.It putwchar output a wide character to a stream 304.It remove remove directory entry 305.It rewind reposition a stream 306.It scanf input format conversion 307.It scanf_l input format conversion 308.It setbuf stream buffering operations 309.It setbuffer stream buffering operations 310.It setlinebuf stream buffering operations 311.It setvbuf stream buffering operations 312.It snprintf formatted output conversion 313.It snprintf_l formatted output conversion 314.It sprintf formatted output conversion 315.It sscanf input format conversion 316.It sscanf_l input format conversion 317.It strerror system error messages 318.It sys_errlist system error messages 319.It sys_nerr system error messages 320.It tempnam temporary file routines 321.It tmpfile temporary file routines 322.It tmpnam temporary file routines 323.It ungetc un-get character from input stream 324.It ungetwc un-get wide character from input stream 325.It vasprintf formatted output conversion with allocation 326.It vasprintf_l formatted output conversion with allocation 327.It vdprintf formatted output conversion 328.It vdprintf_l formatted output conversion 329.It vfprintf formatted output conversion 330.It vfprintf_l formatted output conversion 331.It vfscanf input format conversion 332.It vfscanf_l input format conversion 333.It vprintf formatted output conversion 334.It vprintf_l formatted output conversion 335.It vscanf input format conversion 336.It vscanf_l input format conversion 337.It vsnprintf formatted output conversion 338.It vsnprintf_l formatted output conversion 339.It vsprintf formatted output conversion 340.It vsprintf_l formatted output conversion 341.It vsscanf input format conversion 342.It vsscanf_l input format conversion 343.El 344.Sh BUGS 345The standard buffered functions do not interact well with certain other 346library and system functions, especially 347.Xr vfork 2 348and 349.Xr abort 3 . 350