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1//
2// freopen.cpp
3//
4// Copyright (c) Microsoft Corporation. All rights reserved.
5//
6// Defines the freopen() family of functions, which is used to close a stream
7// and associate it with a new file (typically used for redirecting the
8// standard streams).
9//
10#include <corecrt_internal_stdio.h>
11
12
13
14// Reopens a stream to a new file. If the 'stream' is open, it is closed. The
15// new file, named by 'file_name', is then opened, and 'stream' is associated
16// with that file. The provided 'mode' and 'share_flag' are used when opening
17// the new file. The resulting FILE* is returned via 'result'.
18//
19// Returns 0 on success; returns an error code on failure.
20template <typename Character>
21static errno_t __cdecl common_freopen(
22 FILE** const result,
23 Character const* const file_name,
24 Character const* const mode,
25 __crt_stdio_stream const stream,
26 int const share_flag
27 ) throw()
28{
29 typedef __acrt_stdio_char_traits<Character> stdio_traits;
30
31 _VALIDATE_RETURN_ERRCODE(result != nullptr, EINVAL);
32 *result = nullptr;
33
34 // C11 7.21.5.4/3: "If filename is a null pointer, the freopen function
35 // attempts to change the mode of the stream to that specified by mode, as
36 // if the name of the file currently associated with the stream had been
37 // used. It is implementation-defined which changes of mode are permitted
38 // (if any), and under what circumstances."
39 //
40 // In our implementation, we do not currently support changing the mode
41 // in this way. In the future, we might consider use of ReOpenFile to
42 // implement support for changing the mode.
43 _VALIDATE_RETURN_ERRCODE_NOEXC(file_name != nullptr, EBADF);
44
45 _VALIDATE_RETURN_ERRCODE(mode != nullptr, EINVAL);
46 _VALIDATE_RETURN_ERRCODE(stream.valid() , EINVAL);
47
48 // Just as in the common_fsopen function, we do not hard-validate empty
49 // 'file_name' strings in this function:
50 _VALIDATE_RETURN_ERRCODE_NOEXC(*file_name != 0, EINVAL);
51
52 errno_t return_value = 0;
53
54 _lock_file(stream.public_stream());
55 __try
56 {
57 // If the stream is in use, try to close it, ignoring possible errors:
58 if (stream.is_in_use())
59 _fclose_nolock(stream.public_stream());
60
61 stream->_ptr = nullptr;
62 stream->_base = nullptr;
63 stream->_cnt = 0;
64 stream.unset_flags(-1);
65
66 // We may have called fclose above, which will deallocate the stream.
67 // We still hold the lock on the stream, though, so we can just reset
68 // the allocated flag to retain ownership.
69 stream.set_flags(_IOALLOCATED);
70
71 *result = stdio_traits::open_file(file_name, mode, share_flag, stream.public_stream());
72 if (*result == nullptr)
73 {
74 stream.unset_flags(_IOALLOCATED);
75 return_value = errno;
76 }
77 }
78 __finally
79 {
80 _unlock_file(stream.public_stream());
81 }
82 __endtry
83
84 return return_value;
85}
86
87
88
89extern "C" FILE* __cdecl freopen(
90 char const* const file_name,
91 char const* const mode,
92 FILE* const public_stream
93 )
94{
95 FILE* result_stream = nullptr;
96 common_freopen(&result_stream, file_name, mode, __crt_stdio_stream(public_stream), _SH_DENYNO);
97 return result_stream;
98}
99
100extern "C" errno_t __cdecl freopen_s(
101 FILE** const result,
102 char const* const file_name,
103 char const* const mode,
104 FILE* const public_stream
105 )
106{
107 return common_freopen(result, file_name, mode, __crt_stdio_stream(public_stream), _SH_SECURE);
108}
109
110extern "C" FILE* __cdecl _wfreopen(
111 wchar_t const* const file_name,
112 wchar_t const* const mode,
113 FILE* const public_stream
114 )
115{
116 FILE* result_stream = nullptr;
117 common_freopen(&result_stream, file_name, mode, __crt_stdio_stream(public_stream), _SH_DENYNO);
118 return result_stream;
119}
120
121extern "C" errno_t __cdecl _wfreopen_s(
122 FILE** const result,
123 wchar_t const* const file_name,
124 wchar_t const* const mode,
125 FILE* const public_stream
126 )
127{
128 return common_freopen(result, file_name, mode, __crt_stdio_stream(public_stream), _SH_SECURE);
129}