NAME
fgetln —
get a line from a stream
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
char *
fgetln(FILE
*stream, size_t
*len);
DESCRIPTION
Using this function is error-prone in multiple ways; consider using the safer and more portable function getline(3) instead.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), fgetwln(3), fopen(3), getline(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);
}
if (ferror(fp))
perror("fgetln");