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1//
2// rewind.cpp
3//
4// Copyright (c) Microsoft Corporation. All rights reserved.
5//
6// Defines rewind(), which rewinds a stream.
7//
8#include <corecrt_internal_stdio.h>
9#include <corecrt_internal_ptd_propagation.h>
10
11
12
13// Rewinds a stream back to the beginning, if the stream supports seeking. The
14// stream is flushed and errors are cleared before the rewind.
15static void __cdecl _rewind_internal(FILE* const public_stream, __crt_cached_ptd_host& ptd)
16{
17 __crt_stdio_stream const stream(public_stream);
18
19 _UCRT_VALIDATE_RETURN_VOID(ptd, stream.valid(), EINVAL);
20
21 int const fh = _fileno(stream.public_stream());
22
23 _lock_file(stream.public_stream());
24 __try
25 {
26 // Flush the streeam, reset the error state, and seek back to the
27 // beginning:
28 __acrt_stdio_flush_nolock(stream.public_stream(), ptd);
29 // If the stream is opened in update mode and is currently in use for reading,
30 // the buffer must be abandoned to ensure consistency when transitioning from
31 // reading to writing.
32 // __acrt_stdio_flush_nolock will not reset the buffer when _IOWRITE flag
33 // is not set.
34 __acrt_stdio_reset_buffer(stream);
35
36
37 stream.unset_flags(_IOERROR | _IOEOF);
38 _osfile_safe(fh) &= ~(FEOFLAG);
39
40 if (stream.has_all_of(_IOUPDATE))
41 {
42 stream.unset_flags(_IOREAD | _IOWRITE);
43 }
44
45 if (_lseek_internal(fh, 0, 0, ptd) == -1)
46 {
47 stream.set_flags(_IOERROR);
48 }
49 }
50 __finally
51 {
52 _unlock_file(stream.public_stream());
53 }
54 __endtry
55}
56
57extern "C" void __cdecl rewind(FILE* const public_stream)
58{
59 __crt_cached_ptd_host ptd;
60 _rewind_internal(public_stream, ptd);
61}