+ ASSERT (!fwriting (fp));
+ if (fputc ('x', fp) != 'x')
+ goto skip;
+ ASSERT (fwriting (fp));
+ if (fseek (fp, 0, SEEK_END))
+ goto skip;
+ /* freading (fp) is undefined here, because on some implementations (e.g.
+ glibc) fseek causes a buffer to be read.
+ fwriting (fp) is undefined as well. */
+ if (fclose (fp))
+ goto skip;
+
+ /* Open it in read-write mode. POSIX requires a reposition (fseek,
+ fsetpos, rewind) or fflush when transitioning from write to read,
+ fwriting is only deterministic after input or output, but this
+ test case should be portable even on open, after reposition, and
+ after fflush. */
+ /* Here a scenario that includes fflush. */
+ fp = fopen (TESTFILE, "r+");
+ if (fp == NULL)
+ goto skip;
+ ASSERT (!fwriting (fp));
+ if (fgetc (fp) != 'f')
+ goto skip;
+ ASSERT (!fwriting (fp));
+ if (fseek (fp, 2, SEEK_CUR))
+ goto skip;
+ ASSERT (!fwriting (fp));
+ if (fgetc (fp) != 'b')
+ goto skip;
+ ASSERT (!fwriting (fp));
+ fflush (fp);
+ ASSERT (!fwriting (fp));
+ if (fgetc (fp) != 'x')
+ goto skip;
+ ASSERT (!fwriting (fp));
+ /* This fseek call is necessary when switching from reading to writing.
+ See the description of fopen(), ISO C 99 7.19.5.3.(6). */
+ if (fseek (fp, 0, SEEK_CUR) != 0)
+ goto skip;
+ ASSERT (!fwriting (fp));