NAME
fgetln —
get a line from a stream
SYNOPSIS
#include
<stdio.h>
char *
fgetln(FILE
*stream, size_t
*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 and is guaranteed to be greater than
0 upon successful completion. (Note, however, that if the last line in the
stream 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
HISTORY
The fgetln() function first appeared in
4.4BSD.
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 ‘\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;
lbuf = NULL;
while ((buf = fgetln(fp, &len))) {
if (buf[len - 1] == '\n')
buf[len - 1] = '\0';
else {
/* EOF without EOL, copy and add the NUL */
if ((lbuf = malloc(len + 1)) == NULL)
err(1, NULL);
memcpy(lbuf, buf, len);
lbuf[len] = '\0';
buf = lbuf;
}
printf("%s\n", buf);
}
free(lbuf);