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fgetln(3): Add a Caveats Section

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Reviewed by:	yuripv, bcr (mentor)
Approved by:	bcr (mentror)
Obtained from:	OpenBSD
MFC after:	7 days
Differential Revision:	https://reviews.freebsd.org/D24916
This commit is contained in:
Gordon Bergling 2020-06-18 13:13:04 +00:00
parent 377d7c417a
commit b7d33ccd65
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=362326
1 changed files with 31 additions and 1 deletions
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32
lib/libc/stdio/fgetln.3
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@ -28,7 +28,7 @@
.\" @(#)fgetln.3 8.3 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd February 15, 2016
.Dd June 11, 2020
.Dt FGETLN 3
.Os
.Sh NAME
@ -126,3 +126,33 @@ The
.Fn fgetln
function first appeared in
.Bx 4.4 .
.Sh CAVEATS
Since the returned buffer is not a C string (it is not NUL terminated), a
common practice is to replace the newline character with
.Sq \e0 .
However, if the last line in a file does not contain a newline,
the returned text won't contain a newline either.
The following code demonstrates how to deal with this problem by allocating a
temporary buffer:
.Bd -literal
char *buf, *lbuf;
size_t len;
lbuf = NULL;
while ((buf = fgetln(fp, &len)) != NULL) {
if (buf[len - 1] == '\en')
buf[len - 1] = '\e0';
else {
/* EOF without EOL, copy and add the NUL */
if ((lbuf = malloc(len + 1)) == NULL)
err(1, NULL);
memcpy(lbuf, buf, len);
lbuf[len] = '\e0';
buf = lbuf;
}
printf("%s\en", buf);
}
free(lbuf);
if (ferror(fp))
err(1, "fgetln");
.Ed