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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>