1.\" $OpenBSD: fgets.3,v 1.11 2000/12/24 00:30:58 aaron Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" Chris Torek and the American National Standards Committee X3, 8.\" on Information Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.Dd June 4, 1993 39.Dt FGETS 3 40.Os 41.Sh NAME 42.Nm fgets , 43.Nm gets 44.Nd get a line from a stream 45.Sh SYNOPSIS 46.Fd #include <stdio.h> 47.Ft char * 48.Fn fgets "char *str" "int size" "FILE *stream" 49.Ft char * 50.Fn gets "char *str" 51.Sh DESCRIPTION 52The 53.Fn fgets 54function reads at most one less than the number of characters specified by 55.Xr size 56from the given 57.Fa stream 58and stores them in the string 59.Fa str . 60Reading stops when a newline character is found, 61at end-of-file or error. 62The newline, if any, is retained. 63In any case a 64.Ql \e0 65character is appended to end the string. 66.Pp 67The 68.Fn gets 69function is equivalent to 70.Fn fgets 71with an infinite 72.Xr size 73and a 74.Fa stream 75of 76.Em stdin , 77except that the newline character (if any) is not stored in the string. 78It is the caller's responsibility to ensure that the input line, 79if any, is sufficiently short to fit in the string. 80.Sh RETURN VALUES 81Upon successful completion, 82.Fn fgets 83and 84.Fn gets 85return 86a pointer to the string. 87If end-of-file or an error occurs before any characters are read, 88they return 89.Dv NULL . 90The 91.Fn fgets 92and functions 93.Fn gets 94do not distinguish between end-of-file and error, and callers must use 95.Xr feof 3 96and 97.Xr ferror 3 98to determine which occurred. 99.Sh ERRORS 100.Bl -tag -width Er 101.It Bq Er EBADF 102The given 103.Fa stream 104is not a readable stream. 105.El 106.Pp 107The function 108.Fn fgets 109may also fail and set 110.Va errno 111for any of the errors specified for the routines 112.Xr fflush 3 , 113.Xr fstat 2 , 114.Xr read 2 , 115or 116.Xr malloc 3 . 117.Pp 118The function 119.Fn gets 120may also fail and set 121.Va errno 122for any of the errors specified for the routine 123.Xr getchar 3 . 124.Sh CAVEATS 125The following bit of code illustrates a case where the programmer assumes a 126string is too long if it does not contain a newline: 127.Bd -literal 128 char buf[1024], *p; 129 130 while (fgets(buf, sizeof(buf), fp)) { 131 if (!(p = strchr(buf, '\en'))) { 132 fprintf(stderr, "input line too long.\en"); 133 exit(1); 134 } 135 *p = '\e0'; 136 printf("%s\en", p); 137 } 138.Ed 139.Pp 140While the error would be true if a line > 1023 characters were read, it would 141be false in two other cases: 142.Bl -enum -offset indent 143.It 144If the last line in a file does not contain a newline, the string returned by 145.Fn fgets 146will not contain a newline either. 147Thus 148.Fn strchr 149will return 150.Dv NULL 151and the program will terminate, even if the line was valid. 152.It 153All C string functions, including 154.Fn strchr , 155correctly assume the end of the string is represented by a null 156.Pq Sq \e0 157character. 158If the first character of a line returned by 159.Fn fgets 160were null, 161.Fn strchr 162would immediately return without considering the rest of the returned text 163which may indeed include a newline. 164.El 165.Pp 166Consider using 167.Xr fgetln 3 168instead when dealing with untrusted input. 169.Sh SEE ALSO 170.Xr feof 3 , 171.Xr ferror 3 , 172.Xr fgetln 3 173.Sh STANDARDS 174The functions 175.Fn fgets 176and 177.Fn gets 178conform to 179.St -ansiC . 180.Sh BUGS 181Since it is usually impossible to ensure that the next input line 182is less than some arbitrary length, and because overflowing the 183input buffer is almost invariably a security violation, programs 184should 185.Em NEVER 186use 187.Fn gets . 188The 189.Fn gets 190function exists purely to conform to 191.St -ansiC . 192