tests/ftell_ungetc.c

   1 /* Thanks to the originator of Feedback FB8165838 / Radar 66131999 for
   2  * writing the original version of this test!
   3  */
   4
   5 #include <darwintest.h>
   6
   7 #include <assert.h>
   8 #include <string.h>
   9
  10 #include <stdio.h>
  11
  12 T_DECL(ftell_ungetc, "Test interactions of ftell and ungetc")
  13 {
  14         FILE *fp = stdin;
  15         fp = fopen("assets/ftell_ungetc.txt", "rb");
  16         T_QUIET; T_ASSERT_NE(fp, (FILE*)NULL, "Open the file");
  17
  18         /* Test ftell without having done any reads/writes */
  19         T_ASSERT_EQ(ftell(fp), 0L, "ftell without having done any reads/writes");
  20
  21         /* Read one character */
  22         T_ASSERT_EQ(fgetc(fp), '/', "Read one charatcter");
  23
  24         /* Check ftell again after one read */
  25         T_ASSERT_EQ(ftell(fp), 1L, "ftell after one read");
  26
  27         /* Push back one character */
  28         T_ASSERT_EQ(ungetc('/', fp), '/', "push back one character");
  29
  30         /* Check ftell again after pushing back one char */
  31         T_ASSERT_EQ(ftell(fp), 0L, "ftell after pushing back one char");
  32
  33         /* Read it again */
  34         T_ASSERT_EQ(fgetc(fp), '/', "read pushed back character again");
  35         T_ASSERT_EQ(ftell(fp), 1L, "ftell after reading again");
  36
  37         /* Seek and test ftell again */
  38         T_ASSERT_EQ(fseek(fp, 2, SEEK_SET), 0, "seek");
  39         T_ASSERT_EQ(ftell(fp), 2L, "ftell after seeking");
  40
  41         /* Push back invalid char (EOF) */
  42         T_ASSERT_EQ(ungetc(EOF, fp), EOF, "push back invalid char");
  43         T_ASSERT_EQ(ftell(fp), 2L, "ftell after pushing invalid char, pos should not have changed");
  44
  45         /* Read, push back different char, read again
  46          * and check ftell.
  47          *
  48          * Cppreference:
  49          * A successful call to ungetc on a text stream modifies
  50          * the stream position indicator in unspecified manner but
  51          * guarantees that after all pushed-back characters are
  52          * retrieved with a read operation, the stream position
  53          * indicator is equal to its value before ungetc.
  54          */
  55         T_ASSERT_EQ(fgetc(fp), '-', "read another character");
  56         T_ASSERT_EQ(ftell(fp), 3L, "ftell after read");
  57         T_ASSERT_EQ(ungetc('A', fp), 'A', "push back a different character");
  58         T_ASSERT_EQ(fgetc(fp), 'A', "read back the different character");
  59         T_ASSERT_EQ(ftell(fp), 3L, "ftell after pushback and read back");
  60
  61         /* Push back a non-read character and test ftell.
  62          *
  63          * According to POSIX:
  64          * The file-position indicator is decremented by each
  65          * successful call to ungetc();
  66          *
  67          * Cppreference:
  68          * A successful call to ungetc on a binary stream decrements
  69          * the stream position indicator by one
  70          */
  71         T_ASSERT_EQ(fgetc(fp), '+', "read another character");
  72         T_ASSERT_EQ(ungetc('A', fp), 'A', "push back a different character");
  73         T_EXPECTFAIL; T_ASSERT_EQ(ftell(fp), 3L, "ftell after pushback - EXPECTED FAIL rdar://66131999");
  74 }