NAME
fgetln —
get a line from a
stream
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
char *
fgetln(
FILE *
restrict stream,
size_t *
restrict len);
DESCRIPTION
The
fgetln() function returns a pointer to the next line from
the stream referenced by
stream. This line is
not a C string as it does not end with a terminating
NUL
character. The length of the line, including the
final newline, is stored in the memory location to which
len points. (Note, however, that if the line is the last
in a file that does not end in a newline, the returned text will not contain a
newline.)
RETURN VALUES
Upon successful completion a pointer is returned; this pointer becomes invalid
after the next I/O operation on
stream (whether
successful or not) or as soon as the stream is closed. Otherwise,
NULL
is returned. The
fgetln()
function does not distinguish between end-of-file and error; the routines
feof(3) and
ferror(3) must be used to
determine which occurred. If an error occurs, the global variable
errno is set to indicate the error. The end-of-file
condition is remembered, even on a terminal, and all subsequent attempts to
read will return
NULL
until the condition is cleared
with
clearerr(3).
The text to which the returned pointer points may be modified, provided that no
changes are made beyond the returned size. These changes are lost as soon as
the pointer becomes invalid.
ERRORS
-
-
- [
EBADF
]
- The argument stream is not a stream
open for reading.
The
fgetln() function may also fail and set
errno for any of the errors specified for the routines
fflush(3),
malloc(3),
read(2),
stat(2), or
realloc(3).
SEE ALSO
ferror(3),
fgets(3),
fopen(3),
putc(3)
HISTORY
The
fgetln() function first appeared in
4.4BSD.
CAVEATS
Since the returned buffer is not a C string (it is not null terminated), a
common practice is to replace the newline character with ‘\0’.
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:
char *buf, *lbuf;
size_t len;
while ((lbuf = buf = fgetln(fp, &len)) != NULL) {
if (len > 0 && buf[len - 1] == '\n')
buf[len - 1] = '\0';
else if ((lbuf = strndup(buf, len + 1)) == NULL)
err(1, NULL);
printf("%s\n", lbuf);
if (lbuf != buf)
free(lbuf);
}