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.NET Forum / Languages / Managed C++ / October 2007How do you create an array of pointers to managed types? (C++/CLI)
I have an array cli::array<float, 2> and I would like to access a subset of it's values by compiling an array of pointers. But, it's not possible to create an array of type cli:array<cli::interior_ptr<float>, 2>... So, what do I do? >I have an array cli::array<float, 2> and I would like to access a > subset of it's values by compiling an array of pointers. But, it's not > possible to create an array of type > cli:array<cli::interior_ptr<float>, 2>... > > So, what do I do? I think interior_ptr is a native type so you'd use a normal C++ array (not cli::array). You can make .NET arrays of tracking handles of course (cli::array<T^, 2> where T is a .NET reference type). Of course, you could store integer indices in the array instead of interior_ptr. > <memeticvi...@gmail.com> wrote in message > [quoted text clipped - 13 lines] > Of course, you could store integer indices in the array instead of > interior_ptr. I've tried using an array of tracking handles like this... cli::array<float ^, 2> ^handles; cli::array<float, 2> ^data; data = gcnew cli::array<float, 2>{ {0, 0}, {10, 10}, {20, 20}, {30, 30}, {40, 40}, {50, 50}, {60, 40}, {70, 30}, {80, 20}, {90, 10}, {100, 0} }; handles = gcnew cli::array<float ^, 2>{ {data[0, 0], data[0, 1]}, {data[1, 0], data[1, 1]} }; data[0, 0] = float(100); data[0, 1] = float(100); MessageBox::Show(handles[0, 0]->ToString()); In this case the message box displays 0 instead of 100... I've also tried replacing cli::array<float ^, 2> ^handles; with cli::array<System::Object ^, 2> ^handles; with the same result... >> <memeticvi...@gmail.com> wrote in message >> [quoted text clipped - 48 lines] > I've also tried replacing cli::array<float ^, 2> ^handles; with > cli::array<System::Object ^, 2> ^handles; with the same result... I said "You can make .NET arrays of tracking handles of course (cli::array<T^, 2> where T is a .NET reference type)." The key there is that T must be a reference type. System::Single isn't. As a result, you get boxing, which means an independent copy. Actually, only interior_ptr will let you change the array itself. interior_ptr is a non-fundamental native type, so you can't use it with cli::array. So either: store indices instead of pointers, or use a native array of interior_ptr. > <memeticvi...@gmail.com> wrote in message > [quoted text clipped - 63 lines] > cli::array. So either: store indices instead of pointers, or use a native > array of interior_ptr. "boxing" is the key word. I've been trying to get a grasp on what was happening here for a couple days now. You're a life saver. Given my actual problem, compiling a list of references to individual values in a data set, the "store indices" option is out. It would be to complex. So, I'm trying to figure how to store a list of type interior_ptr. I'm having some difficulty getting it to work though. Could you provide me with an example? > <memeticvi...@gmail.com> wrote in message > [quoted text clipped - 63 lines] > cli::array. So either: store indices instead of pointers, or use a native > array of interior_ptr. System::Collections::ArrayList ^pointers = gcnew System::Collections::ArrayList; pointers->Add(&data[0,0]); /* error C2664: 'System::Collections::ArrayList::Add' : cannot convert parameter 1 from 'cli::interior_ptr<Type>' to 'System::Object ^' */ >> I said "You can make .NET arrays of tracking handles of course >> (cli::array<T^, 2> where T is a .NET reference type)." [quoted text clipped - 18 lines] > parameter 1 from 'cli::interior_ptr<Type>' to 'System::Object ^' > */ A native array of interior_ptr, like perhaps: std::vector<cli::interior_ptr<float>> pointers; pointers.push_back(&data[0,0]); > >> I said "You can make .NET arrays of tracking handles of course > >> (cli::array<T^, 2> where T is a .NET reference type)." [quoted text clipped - 23 lines] > std::vector<cli::interior_ptr<float>> pointers; > pointers.push_back(&data[0,0]); A native array can not contain a managed type (cli::interior_ptr) >> >> I said "You can make .NET arrays of tracking handles of course >> >> (cli::array<T^, 2> where T is a .NET reference type)." [quoted text clipped - 27 lines] > > A native array can not contain a managed type (cli::interior_ptr) Ahh... the interior_ptr declaration clearly states that this isn't possible. interior_ptr can only be used as a local variable. Looks like storing indices is your only option. > <memeticvi...@gmail.com> wrote in message > [quoted text clipped - 36 lines] > > Looks like storing indices is your only option. The amount of complexity this would introduce into my project is unreasonable. First of all I'd have to store references to a DataSet the name of the DataTable, the name of the DataColumn and the index of the DataRow. And, then what if something changes? Well then I have to reprocess and redraw everything? The data my program is used to process is usually incredibly vast and complicated. Consisting of hundreds of thousands DataRows. Is garbage collection worth bring a system to it's knees every time some one changes a digit in a DataGridView or something? This is stupid! There has to be a way to create an array of references to the memory locations of the individual values in the DataSet. I won't accept that there isn't a better way to do this. I could do it in with 3 lines of code in standard C++! >> <memeticvi...@gmail.com> wrote in message >> [quoted text clipped - 42 lines] > the name of the DataTable, the name of the DataColumn and the index of > the DataRow. And, then what if something changes? Well then I have to Why? If you have an array<float,2>, why not store a handle to the array, and the row and column indices? > reprocess and redraw everything? The data my program is used to > process is usually incredibly vast and complicated. Consisting of [quoted text clipped - 8 lines] > there isn't a better way to do this. I could do it in with 3 lines of > code in standard C++! > <memeticvi...@gmail.com> wrote in message > [quoted text clipped - 62 lines] > > there isn't a better way to do this. I could do it in with 3 lines of > > code in standard C++! Because, the indices change whenever something is inserted or removed... And, then I'd have to reprocess the data. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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