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.Dd June 11, 2020 29.Dt FGETLN 3 30.Os 31.Sh NAME 32.Nm fgetln 33.Nd get a line from a stream 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In stdio.h 38.Ft char * 39.Fn fgetln "FILE *stream" "size_t *len" 40.Sh DESCRIPTION 41The 42.Fn fgetln 43function 44returns a pointer to the next line from the stream referenced by 45.Fa stream . 46This line is 47.Em not 48a C string as it does not end with a terminating 49.Dv NUL 50character. 51The length of the line, including the final newline, 52is stored in the memory location to which 53.Fa len 54points. 55(Note, however, that if the line is the last 56in a file that does not end in a newline, 57the returned text will not contain a newline.) 58.Sh RETURN VALUES 59Upon successful completion a pointer is returned; 60this pointer becomes invalid after the next 61.Tn I/O 62operation on 63.Fa stream 64(whether successful or not) 65or as soon as the stream is closed. 66Otherwise, 67.Dv NULL 68is returned. 69The 70.Fn fgetln 71function 72does not distinguish between end-of-file and error; the routines 73.Xr feof 3 74and 75.Xr ferror 3 76must be used 77to determine which occurred. 78If an error occurs, the global variable 79.Va errno 80is set to indicate the error. 81The end-of-file condition is remembered, even on a terminal, and all 82subsequent attempts to read will return 83.Dv NULL 84until the condition is 85cleared with 86.Xr clearerr 3 . 87.Pp 88The text to which the returned pointer points may be modified, 89provided that no changes are made beyond the returned size. 90These changes are lost as soon as the pointer becomes invalid. 91.Sh ERRORS 92.Bl -tag -width Er 93.It Bq Er EBADF 94The argument 95.Fa stream 96is not a stream open for reading. 97.It Bq Er ENOMEM 98The internal line buffer could not be expanded due to lack of available memory, 99or because it would need to expand beyond INT_MAX in size. 100.El 101.Pp 102The 103.Fn fgetln 104function 105may also fail and set 106.Va errno 107for any of the errors specified for the routines 108.Xr fflush 3 , 109.Xr malloc 3 , 110.Xr read 2 , 111.Xr stat 2 , 112or 113.Xr realloc 3 . 114.Sh SEE ALSO 115.Xr ferror 3 , 116.Xr fgets 3 , 117.Xr fgetwln 3 , 118.Xr fopen 3 , 119.Xr getline 3 , 120.Xr putc 3 121.Sh HISTORY 122The 123.Fn fgetln 124function first appeared in 125.Bx 4.4 . 126.Sh CAVEATS 127Since the returned buffer is not a C string (it is not NUL terminated), a 128common practice is to replace the newline character with 129.Sq \e0 . 130However, if the last line in a file does not contain a newline, 131the returned text won't contain a newline either. 132The following code demonstrates how to deal with this problem by allocating a 133temporary buffer: 134.Bd -literal 135 char *buf, *lbuf; 136 size_t len; 137 138 lbuf = NULL; 139 while ((buf = fgetln(fp, &len)) != NULL) { 140 if (buf[len - 1] == '\en') 141 buf[len - 1] = '\e0'; 142 else { 143 /* EOF without EOL, copy and add the NUL */ 144 if ((lbuf = malloc(len + 1)) == NULL) 145 err(1, NULL); 146 memcpy(lbuf, buf, len); 147 lbuf[len] = '\e0'; 148 buf = lbuf; 149 } 150 printf("%s\en", buf); 151 } 152 free(lbuf); 153 if (ferror(fp)) 154 err(1, "fgetln"); 155.Ed 156