1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)fgetln.3 8.3 (Berkeley) 4/19/94 29.\" $FreeBSD: src/lib/libc/stdio/fgetln.3,v 1.10 2009/02/28 06:00:58 das Exp $ 30.\" 31.Dd January 16, 2019 32.Dt FGETLN 3 33.Os 34.Sh NAME 35.Nm fgetln 36.Nd get a line from a stream 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In stdio.h 41.Ft char * 42.Fn fgetln "FILE *stream" "size_t *len" 43.Sh DESCRIPTION 44Using this function is error-prone in multiple ways; 45consider using the safer and more portable function 46.Xr getline 3 47instead. 48.Pp 49The 50.Fn fgetln 51function 52returns a pointer to the next line from the stream referenced by 53.Fa stream . 54This line is 55.Em not 56a C string as it does not end with a terminating 57.Dv NUL 58character. 59The length of the line, including the final newline, 60is stored in the memory location to which 61.Fa len 62points. 63(Note, however, that if the line is the last 64in a file that does not end in a newline, 65the returned text will not contain a newline.) 66.Sh RETURN VALUES 67Upon successful completion a pointer is returned; 68this pointer becomes invalid after the next 69.Tn I/O 70operation on 71.Fa stream 72(whether successful or not) 73or as soon as the stream is closed. 74Otherwise, 75.Dv NULL 76is returned. 77The 78.Fn fgetln 79function 80does not distinguish between end-of-file and error; the routines 81.Xr feof 3 82and 83.Xr ferror 3 84must be used 85to determine which occurred. 86If an error occurs, the global variable 87.Va errno 88is set to indicate the error. 89The end-of-file condition is remembered, even on a terminal, and all 90subsequent attempts to read will return 91.Dv NULL 92until the condition is 93cleared with 94.Xr clearerr 3 . 95.Pp 96The text to which the returned pointer points may be modified, 97provided that no changes are made beyond the returned size. 98These changes are lost as soon as the pointer becomes invalid. 99.Sh ERRORS 100.Bl -tag -width Er 101.It Bq Er EBADF 102The argument 103.Fa stream 104is not a stream open for reading. 105.El 106.Pp 107The 108.Fn fgetln 109function 110may also fail and set 111.Va errno 112for any of the errors specified for the routines 113.Xr fflush 3 , 114.Xr malloc 3 , 115.Xr read 2 , 116.Xr stat 2 , 117or 118.Xr realloc 3 . 119.Sh SEE ALSO 120.Xr ferror 3 , 121.Xr fgets 3 , 122.Xr fgetwln 3 , 123.Xr fopen 3 , 124.Xr getline 3 , 125.Xr putc 3 126.Sh HISTORY 127The 128.Fn fgetln 129function first appeared in 130.Bx 4.4 . 131.Sh CAVEATS 132Since the returned buffer is not a C string (it is not null terminated), a 133common practice is to replace the newline character with 134.Sq \e0 . 135However, if the last line in a file does not contain a newline, 136the returned text won't contain a newline either. 137The following code demonstrates how to deal with this problem by allocating a 138temporary buffer: 139.Bd -literal 140 char *buf, *lbuf; 141 size_t len; 142 143 while ((lbuf = buf = fgetln(fp, &len)) != NULL) { 144 if (len > 0 && buf[len - 1] == '\en') 145 buf[len - 1] = '\e0'; 146 else if ((lbuf = strndup(buf, len + 1)) == NULL) 147 err(1, NULL); 148 printf("%s\en", lbuf); 149 150 if (lbuf != buf) 151 free(lbuf); 152 } 153 if (ferror(fp)) 154 perror("fgetln"); 155.Ed 156