MirBSD manpage: fgetln(3)

FGETLN(3)                  BSD Programmer's Manual                   FGETLN(3)


     fgetln - get a line from a stream


     #include <stdio.h>

     char *
     fgetln(FILE *stream, size_t *len);


     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 and is
     guaranteed to be greater than 0 upon successful completion. (Note, howev-
     er, that if the last line in the stream does not end in a newline, the
     returned text will not contain a newline.)


     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 oc-
     curred. 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.


     [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


     ferror(3), fgets(3), fopen(3), fparseln(3), putc(3)


     The fgetln() function first appeared in 4.4BSD.


     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
     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 {
                             /* EOF without EOL, copy and add the NUL */
                             if ((lbuf = realloc(lbuf, len + 1)) == NULL)
                                     /* XXX bad realloc example though */
                                     err(1, NULL);
                             memcpy(lbuf, buf, len);
                             lbuf[len] = '\0';
                             buf = lbuf;
                     printf("%s\n", buf);

MirBSD #10-current            November 21, 2009                              1

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