fgetln(3) - NetBSD Manual Pages

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FGETLN(3)               NetBSD 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 indi-
     cate the error.  The end-of-file condition is remembered, even on a ter-
     minal, 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'.  How-
     ever, 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);
             }

NetBSD 10.1                      July 4, 2018                      NetBSD 10.1