1 | /* |
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2 | * Copyright (c) 1990 The Regents of the University of California. |
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3 | * All rights reserved. |
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4 | * |
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5 | * Redistribution and use in source and binary forms are permitted |
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6 | * provided that the above copyright notice and this paragraph are |
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7 | * duplicated in all such forms and that any documentation, |
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8 | * advertising materials, and other materials related to such |
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9 | * distribution and use acknowledge that the software was developed |
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10 | * by the University of California, Berkeley. The name of the |
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11 | * University may not be used to endorse or promote products derived |
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12 | * from this software without specific prior written permission. |
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13 | * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR |
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14 | * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED |
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15 | * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. |
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16 | */ |
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17 | |
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18 | /* |
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19 | FUNCTION |
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20 | <<ftell>>, <<ftello>>---return position in a stream or file |
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21 | |
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22 | INDEX |
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23 | ftell |
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24 | INDEX |
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25 | ftello |
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26 | INDEX |
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27 | _ftell_r |
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28 | INDEX |
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29 | _ftello_r |
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30 | |
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31 | SYNOPSIS |
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32 | #include <stdio.h> |
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33 | long ftell(FILE *<[fp]>); |
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34 | off_t ftello(FILE *<[fp]>); |
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35 | long _ftell_r(struct _reent *<[ptr]>, FILE *<[fp]>); |
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36 | off_t _ftello_r(struct _reent *<[ptr]>, FILE *<[fp]>); |
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37 | |
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38 | DESCRIPTION |
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39 | Objects of type <<FILE>> can have a ``position'' that records how much |
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40 | of the file your program has already read. Many of the <<stdio>> functions |
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41 | depend on this position, and many change it as a side effect. |
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42 | |
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43 | The result of <<ftell>>/<<ftello>> is the current position for a file |
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44 | identified by <[fp]>. If you record this result, you can later |
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45 | use it with <<fseek>>/<<fseeko>> to return the file to this |
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46 | position. The difference between <<ftell>> and <<ftello>> is that |
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47 | <<ftell>> returns <<long>> and <<ftello>> returns <<off_t>>. |
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48 | |
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49 | In the current implementation, <<ftell>>/<<ftello>> simply uses a character |
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50 | count to represent the file position; this is the same number that |
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51 | would be recorded by <<fgetpos>>. |
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52 | |
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53 | RETURNS |
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54 | <<ftell>>/<<ftello>> return the file position, if possible. If they cannot do |
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55 | this, they return <<-1L>>. Failure occurs on streams that do not support |
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56 | positioning; the global <<errno>> indicates this condition with the |
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57 | value <<ESPIPE>>. |
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58 | |
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59 | PORTABILITY |
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60 | <<ftell>> is required by the ANSI C standard, but the meaning of its |
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61 | result (when successful) is not specified beyond requiring that it be |
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62 | acceptable as an argument to <<fseek>>. In particular, other |
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63 | conforming C implementations may return a different result from |
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64 | <<ftell>> than what <<fgetpos>> records. |
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65 | |
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66 | <<ftello>> is defined by the Single Unix specification. |
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67 | |
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68 | No supporting OS subroutines are required. |
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69 | */ |
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70 | |
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71 | #if defined(LIBC_SCCS) && !defined(lint) |
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72 | static char sccsid[] = "%W% (Berkeley) %G%"; |
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73 | #endif /* LIBC_SCCS and not lint */ |
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74 | |
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75 | /* |
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76 | * ftell: return current offset. |
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77 | */ |
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78 | |
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79 | #include <_ansi.h> |
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80 | #include <reent.h> |
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81 | #include <stdio.h> |
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82 | #include <errno.h> |
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83 | #include "local.h" |
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84 | |
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85 | long |
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86 | _ftell_r (struct _reent *ptr, |
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87 | register FILE * fp) |
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88 | { |
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89 | _fpos_t pos; |
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90 | |
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91 | pos = _ftello_r (ptr, fp); |
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92 | if ((long)pos != pos) |
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93 | { |
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94 | pos = -1; |
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95 | ptr->_errno = EOVERFLOW; |
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96 | } |
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97 | return (long)pos; |
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98 | } |
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99 | |
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100 | #ifndef _REENT_ONLY |
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101 | |
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102 | long |
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103 | ftell (register FILE * fp) |
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104 | { |
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105 | return _ftell_r (_REENT, fp); |
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106 | } |
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107 | |
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108 | #endif /* !_REENT_ONLY */ |
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