{"id":2086,"date":"2020-07-16T09:50:27","date_gmt":"2020-07-16T07:50:27","guid":{"rendered":"https:\/\/alax.info\/blog\/?p=2086"},"modified":"2020-07-16T13:21:17","modified_gmt":"2020-07-16T11:21:17","slug":"c-winrt-version-of-setfiletime","status":"publish","type":"post","link":"https:\/\/alax.info\/blog\/2086","title":{"rendered":"C++\/WinRT version of SetFileTime"},"content":{"rendered":"\n

SetFileTime<\/a><\/code> is simple and does not deserve a blog post: you have a file handle, you have date\/time, you set it.<\/p>\n\n\n\n

StorageFile File { ... };\nFILETIME DateCreatedFileTime = ...;\nwinrt::file_handle File { CreateFile(File.Path().c_str(), GENERIC_WRITE, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr) };\nwinrt::check_bool(SetFileTime(File.get(), &DateCreatedFileTime, &DateCreatedFileTime, &DateCreatedFileTime));<\/code><\/pre>\n\n\n\n
C++\/WinRT and UWP make the journey much more exciting.<\/p>\n\n\n\n
There is StorageItemContentProperties<\/code> Class<\/a> which provides access to the content-related properties of an item (like a file or folder). This includes file times which are exposed as named properties, like “System.DateModified”<\/a>. StorageItemContentProperties.SavePropertiesAsync<\/code> Method<\/a> is to save properties associated with the item.<\/p>\n\n\n\n
SavePropertiesAsync<\/code> is asynchronous so you have to deal with this too, but it is not to worry since C++\/WinRT does not let you down with this at least.<\/p>\n\n\n\n
One another thing is you need a Windows::Foundation::DateTime<\/code><\/a> value for the time which is something you might be not have good understanding for, as opposed to old fashioned FILETIME'<\/code>s definition<\/a> of “a 64-bit value representing the number of 100-nanosecond intervals since January 1, 1601 (UTC)”.<\/p>\n\n\n\n
In C++\/WinRT Windows::Foundation::DateTime<\/code> is directly mapped to std::chrono::time_point<\/code> and there is also winrt::clock<\/code><\/a> as well, and conversion helpers which are easy to use but you have to be aware of them.<\/p>\n\n\n\n
Moving on? With Windows::Foundation::DateTime<\/code><\/a> value on hands you need to put it into a key-value collection of properties to save. However, since values, in general, might be of different types you need to convert the time to variant<\/s> IInspectable<\/code>. That is, to “box”<\/a> it. Luckily, C++\/WinRT has it all for you already:<\/p>\n\n\n\n
C++\/WinRT<\/a> provides the winrt::box_value<\/strong><\/a> function, which takes a scalar value and returns the value boxed into an IInspectable<\/strong>. For unboxing an IInspectable<\/strong> back into a scalar value, there are the winrt::unbox_value<\/strong><\/a> and winrt::unbox_value_or<\/strong><\/a> functions.<\/p><\/blockquote>\n\n\n\n
Now we reached a hard one. SavePropertiesAsync<\/code> signature is this:<\/p>\n\n\n\n
...SavePropertiesAsync(param::async_iterable<Windows::Foundation::Collections::IKeyValuePair<hstring, Windows::Foundation::IInspectable>> const& propertiesToSave) const\n{\n  ...\n}<\/code><\/pre>\n\n\n\n
So IInspectable<\/code> there is the boxed value. This needs to be taken into something convertible to Windows::Foundation::Collections::IKeyValuePair<\/code> which is already a bit scary. But the truth is the real bastard is param::async_iterable<\/code>.<\/p>\n\n\n\n
I have to admit MSDN documentation for C++\/WinRT is awesome. There are so many things already mentioned there, including, for example, this article: Standard C++ data types and C++\/WinRT<\/a>, which is relevant and helpful. C++\/WinRT is awesome too. <\/p>\n\n\n\n
So you might think you could just have a std::map and it will be converted to Windows::Foundation::Collections::IKeyValuePair<\/code> automagically and then it would be picked up by param::async_iterable<\/code> as an argument? No. <\/p>\n\n\n\n
[...]\nerror C2664: 'winrt::Windows::Foundation::IAsyncAction winrt::impl::consume_Windows_Storage_FileProperties_IStorageItemExtraProperties::SavePropertiesAsync(void) const': cannot convert argument 1 from 'std::map,std::allocator>>' to 'const winrt::param::async_iterable> &'\n[...]\nReason: cannot convert from 'std::map,std::allocator>>' to 'const winrt::param::async_iterable>'\n[...]\nNo user-defined-conversion operator available that can perform this conversion, or the operator cannot be called<\/pre>\n\n\n\n
The thing is, and it’s mentioned here<\/a>, for example, that async_iterable<\/code> need to acquire ownership of the collection when it takes it as an argument in a thin and lightweight way. So you have got to std::move<\/code> it there before the code starts building.<\/p>\n\n\n\n
What do we got? Thing do build and call UWP API correctly. Everything is important here:<\/p>\n\n\n\n
StorageFile File { ... };\nFILETIME DateCreatedFileTime = ...;\nstd::map<winrt::hstring, winrt::Windows::Foundation::IInspectable> PropertyMap;\nPropertyMap.emplace(L\"System.DateModified\", winrt::box_value(winrt::clock::from_file_time(DateCreatedFileTime)));\nFile.Properties().SavePropertiesAsync(std::move(PropertyMap)).get();<\/code><\/pre>\n\n\n\n
Now the problem is that runtime behavior is this: E_INVALIDARG<\/code> 0x80070057 : ‘Cannot write to the specified property (System.DateModified). The property is read-only.’.<\/p>\n\n\n\n
That is, you don’t change\/save this property from UWP<\/a>. <\/p>\n","protected":false},"excerpt":{"rendered":"
SetFileTime is simple and does not deserve a blog post: you have a file handle, you have date\/time, you set it. C++\/WinRT and UWP make the journey much more exciting. There is StorageItemContentProperties Class which provides access to the content-related properties of an item (like a file or folder). This includes file times which are… <\/p>\n
Read the full article<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[588,581],"class_list":["post-2086","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-c-winrt","tag-winapi-2"],"_links":{"self":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts\/2086","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/comments?post=2086"}],"version-history":[{"count":0,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/posts\/2086\/revisions"}],"wp:attachment":[{"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/media?parent=2086"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/categories?post=2086"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/alax.info\/blog\/wp-json\/wp\/v2\/tags?post=2086"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}