fgetln (original) (raw)

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FGETLN(3) 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_, _sizet_ _*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, in- cluding 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 er- ror; 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 in- dicate 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 read- ing.

   [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)](/cgi/man.cgi?query=fflush&sektion=3&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports), [_malloc_(3)](/cgi/man.cgi?query=malloc&sektion=3&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports),	[_read_(2)](/cgi/man.cgi?query=read&sektion=2&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports),  [_stat_(2)](/cgi/man.cgi?query=stat&sektion=2&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports),  or
   [_realloc_(3)](/cgi/man.cgi?query=realloc&sektion=3&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports).

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'. How- ever, if the last line in a file does not contain a newline, the re- turned text won't contain a newline either. The following code demon- strates how to deal with this problem by allocating a temporary buffer:

       char *buf, *lbuf;
       size_t len;

       lbuf = NULL;
       while ((buf = fgetln(fp,	&len)) != NULL)	{
           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)](/cgi/man.cgi?query=free&sektion=lbuf&apropos=0&manpath=FreeBSD+14.3-RELEASE+and+Ports);
       if (ferror(fp))
           err(1, "fgetln");

FreeBSD 14.3 June 11, 2020 FGETLN(3)

NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUES |ERRORS |SEE ALSO |HISTORY |CAVEATS

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