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NetBSD 6.1.5 - man page for fgetln (netbsd section 3)

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FGETLN(3)			   BSD 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 * 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;

	     lbuf = NULL;
	     while ((buf = fgetln(fp, &len))) {
		     if (buf[len - 1] == '\n')
			     buf[len - 1] = '\0';
		     else {
			     if ((lbuf = (char *)malloc(len + 1)) == NULL)
				     err(1, NULL);
			     memcpy(lbuf, buf, len);
			     lbuf[len] = '\0';
			     buf = lbuf;
		     }
		     printf("%s\n", buf);

		     if (lbuf != NULL) {
			     free(lbuf);
			     lbuf = NULL;
		     }
	     }

BSD					  April 21, 2004				      BSD
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