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FGETLN(3) FreeBSD Library Functions Manual FGETLN(3)
NAME
fgetln - get a line from a stream
LIBRARY
Standard C Library (libc, -lc)
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.
(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.
[ENOMEM] The internal line buffer could not be expanded due to
lack of available memory, or because it would need to
expand beyond INT_MAX in size.
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 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
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);
if (ferror(fp))
err(1, "fgetln");
FreeBSD 14.2-RELEASE June 11, 2020 FreeBSD 14.2-RELEASE