glibc/libio/bug-ungetc.c

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/* Test program for ungetc/ftell interaction bug. */
#include <stdio.h>
#include <support/xunistd.h>
static void do_prepare (void);
#define PREPARE(argc, argv) do_prepare ()
static int do_test (void);
#define TEST_FUNCTION do_test ()
#include <test-skeleton.c>
static const char pattern[] = "12345";
static char *temp_file;
static void
do_prepare (void)
{
int fd = create_temp_file ("bug-ungetc.", &temp_file);
if (fd == -1)
{
printf ("cannot create temporary file: %m\n");
exit (1);
}
xwrite (fd, pattern, sizeof (pattern));
close (fd);
}
static int
do_test (void)
{
int i;
FILE *f;
char buf[10];
long offset, diff;
int result = 0;
f = fopen (temp_file, "rw");
rewind (f);
for (i = 0; i < 3; i++)
printf ("%c\n", getc (f));
offset = ftell (f);
printf ("offset = %ld\n", offset);
if (ungetc ('4', f) != '4')
{
printf ("ungetc failed\n");
abort ();
}
printf ("offset after ungetc = %ld\n", ftell (f));
i = fread ((void *) buf, 4, (size_t) 1, f);
printf ("read %d (%c), offset = %ld\n", i, buf[0], ftell (f));
diff = ftell (f) - offset;
if (diff != 3)
{
printf ("ftell did not update properly. got %ld, expected 3\n", diff);
result = 1;
}
fclose (f);
return result;
}