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/* Bug 1190: EOF conditions are supposed to be sticky.
Copyright (C) 2018 Free Software Foundation.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. This file is offered as-is,
without any warranty. */
/* ISO C1999 specification of fgetc:
#include <stdio.h>
int fgetc (FILE *stream);
Description
If the end-of-file indicator for the input stream pointed to by
stream is not set and a next character is present, the fgetc
function obtains that character as an unsigned char converted to
an int and advances the associated file position indicator for
the stream (if defined).
Returns
If the end-of-file indicator for the stream is set, or if the
stream is at end-of-file, the end-of-file indicator for the
stream is set and the fgetc function returns EOF. Otherwise, the
fgetc function returns the next character from the input stream
pointed to by stream. If a read error occurs, the error indicator
for the stream is set and the fgetc function returns EOF.
The requirement to return EOF "if the end-of-file indicator for the
stream is set" was new in C99; the language in the 1989 edition of
the standard was ambiguous. Historically, BSD-derived Unix always
had the C99 behavior, whereas in System V fgetc would attempt to
call read() again before returning EOF again. Prior to version 2.28,
glibc followed the System V behavior even though this does not
comply with C99.
See
<https://sourceware.org/bugzilla/show_bug.cgi?id=1190>,
<https://sourceware.org/bugzilla/show_bug.cgi?id=19476>,
and the thread at
<https://sourceware.org/ml/libc-alpha/2012-09/msg00343.html>
for more detail. */
#include <support/tty.h>
#include <support/check.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#define XWRITE(fd, s, msg) do { \
if (write (fd, s, sizeof s - 1) != sizeof s - 1) \
{ \
perror ("write " msg); \
return 1; \
} \
} while (0)
int
do_test (void)
{
/* The easiest way to set up the conditions under which you can
notice whether the end-of-file indicator is sticky, is with a
pseudo-tty. This is also the case which applications are most
likely to care about. And it avoids any question of whether and
how it is legitimate to access the same physical file with two
independent FILE objects. */
int outer_fd, inner_fd;
FILE *fp;
support_openpty (&outer_fd, &inner_fd, 0, 0, 0);
fp = fdopen (inner_fd, "r+");
if (!fp)
{
perror ("fdopen");
return 1;
}
XWRITE (outer_fd, "abc\n\004", "first line + EOF");
TEST_COMPARE (fgetc (fp), 'a');
TEST_COMPARE (fgetc (fp), 'b');
TEST_COMPARE (fgetc (fp), 'c');
TEST_COMPARE (fgetc (fp), '\n');
TEST_COMPARE (fgetc (fp), EOF);
TEST_VERIFY_EXIT (feof (fp));
TEST_VERIFY_EXIT (!ferror (fp));
XWRITE (outer_fd, "d\n", "second line");
/* At this point, there is a new full line of input waiting in the
kernelside input buffer, but we should still observe EOF from
stdio, because the end-of-file indicator has not been cleared. */
TEST_COMPARE (fgetc (fp), EOF);
/* Clearing EOF should reveal the next line of input. */
clearerr (fp);
TEST_COMPARE (fgetc (fp), 'd');
TEST_COMPARE (fgetc (fp), '\n');
fclose (fp);
close (outer_fd);
return 0;
}
#include <support/test-driver.c>
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