xref: /openbsd/lib/libc/stdio/fgetln.3 (revision 404b540a)
1.\"	$OpenBSD: fgetln.3,v 1.15 2007/06/21 13:47:07 moritz Exp $
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30.Dd $Mdocdate: June 21 2007 $
31.Dt FGETLN 3
32.Os
33.Sh NAME
34.Nm fgetln
35.Nd get a line from a stream
36.Sh SYNOPSIS
37.Fd #include <stdio.h>
38.Ft char *
39.Fn fgetln "FILE *stream" "size_t *len"
40.Sh DESCRIPTION
41The
42.Fn fgetln
43function returns a pointer to the next line from the stream referenced by
44.Fa stream .
45This line is
46.Em not
47a C string as it does not end with a terminating
48.Tn NUL
49character.
50The length of the line, including the final newline,
51is stored in the memory location to which
52.Fa len
53points and is guaranteed to be greater than 0 upon successful completion.
54(Note, however, that if the last line in the stream does not end in a newline,
55the returned text will not contain a newline.)
56.Sh RETURN VALUES
57Upon successful completion a pointer is returned;
58this pointer becomes invalid after the next
59.Tn I/O
60operation on
61.Fa stream
62(whether successful or not)
63or as soon as the stream is closed.
64Otherwise,
65.Dv NULL
66is returned.
67.Pp
68The
69.Fn fgetln
70function does not distinguish between end-of-file and error; the routines
71.Xr feof 3
72and
73.Xr ferror 3
74must be used
75to determine which occurred.
76If an error occurs, the global variable
77.Va errno
78is set to indicate the error.
79The end-of-file condition is remembered, even on a terminal, and all
80subsequent attempts to read will return
81.Dv NULL
82until the condition is
83cleared with
84.Xr clearerr 3 .
85.Pp
86The text to which the returned pointer points may be modified,
87provided that no changes are made beyond the returned size.
88These changes are lost as soon as the pointer becomes invalid.
89.Sh ERRORS
90.Bl -tag -width [EBADF]
91.It Bq Er EBADF
92The argument
93.Fa stream
94is not a stream open for reading.
95.El
96.Pp
97The
98.Fn fgetln
99function may also fail and set
100.Va errno
101for any of the errors specified for the routines
102.Xr fflush 3 ,
103.Xr malloc 3 ,
104.Xr read 2 ,
105.Xr stat 2 ,
106or
107.Xr realloc 3 .
108.Sh SEE ALSO
109.Xr ferror 3 ,
110.Xr fgets 3 ,
111.Xr fopen 3 ,
112.Xr fparseln 3 ,
113.Xr putc 3
114.Sh HISTORY
115The
116.Fn fgetln
117function first appeared in
118.Bx 4.4 .
119.Sh CAVEATS
120Since the returned buffer is not a C string (it is not NUL terminated), a
121common practice is to replace the newline character with
122.Sq \e0 .
123However, if the last line in a file does not contain a newline,
124the returned text won't contain a newline either.
125The following code demonstrates how to deal with this problem by allocating a
126temporary buffer:
127.Bd -literal
128	char *buf, *lbuf;
129	size_t len;
130
131	lbuf = NULL;
132	while ((buf = fgetln(fp, &len))) {
133		if (buf[len - 1] == '\en')
134			buf[len - 1] = '\e0';
135		else {
136			/* EOF without EOL, copy and add the NUL */
137			if ((lbuf = malloc(len + 1)) == NULL)
138				err(1, NULL);
139			memcpy(lbuf, buf, len);
140			lbuf[len] = '\e0';
141			buf = lbuf;
142		}
143		printf("%s\en", buf);
144	}
145	free(lbuf);
146.Ed
147