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  • Why use buffers to read/write Streams

    - by James Hay
    Following reading various questions on reading and writing Streams, all the various answers define something like this as the correct way to do it: private void CopyStream(Stream input, Stream output) { byte[] buffer = new byte[16 * 1024]; int read; while ((read = input.Read(buffer, 0, buffer.Length)) > 0) { output.Write(buffer, 0, read); } } Two questions: Why read and write in these smaller chunks? What is the significance of the buffer size used?

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  • Are there any platforms where using structure copy on an fd_set (for select() or pselect()) causes p

    - by Jonathan Leffler
    The select() and pselect() system calls modify their arguments (the 'struct fd_set *' arguments), so the input value tells the system which file descriptors to check and the return values tell the programmer which file descriptors are currently usable. If you are going to call them repeatedly for the same set of file descriptors, you need to ensure that you have a fresh copy of the descriptors for each call. The obvious way to do that is to use a structure copy: struct fd_set ref_set_rd; struct fd_set ref_set_wr; struct fd_set ref_set_er; ... ...code to set the reference fd_set_xx values... ... while (!done) { struct fd_set act_set_rd = ref_set_rd; struct fd_set act_set_wr = ref_set_wr; struct fd_set act_set_er = ref_set_er; int bits_set = select(max_fd, &act_set_rd, &act_set_wr, &act_set_er, &timeout); if (bits_set > 0) { ...process the output values of act_set_xx... } } My question: Are there any platforms where it is not safe to do a structure copy of the struct fd_set values as shown? I'm concerned lest there be hidden memory allocation or anything unexpected like that. (There are macros/functions FD_SET(), FD_CLR(), FD_ZERO() and FD_ISSET() to mask the internals from the application.) I can see that MacOS X (Darwin) is safe; other BSD-based systems are likely to be safe, therefore. You can help by documenting other systems that you know are safe in your answers. (I do have minor concerns about how well the struct fd_set would work with more than 8192 open file descriptors - the default maximum number of open files is only 256, but the maximum number is 'unlimited'. Also, since the structures are 1 KB, the copying code is not dreadfully efficient, but then running through a list of file descriptors to recreate the input mask on each cycle is not necessarily efficient either. Maybe you can't do select() when you have that many file descriptors open, though that is when you are most likely to need the functionality.) There's a related SO question - asking about 'poll() vs select()' which addresses a different set of issues from this question.

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  • Does variable = null set it for garbage collection

    - by manyxcxi
    Help me settle a dispute with a coworker: Does setting a variable or collection to null in Java aid in garbage collection and reducing memory usage? If I have a long running program and each function may be iteratively called (potentially thousands of times): Does setting all the variables in it to null before returning a value to the parent function help reduce heap size/memory usage?

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  • Changing printer preference using vb6?

    - by Mahmoud
    I am having a problem when my program is installed to another computer, where its printer preference is different, where my data report accepts Letter size 8.2 * 11 in, because when the printer preference is different the data report well not show and gives an error saying the page width is larger than paper width, does anyone know how to fix this problem. i tried this code but it didn't work Printer.PaperSize = vbPRPSLetter

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  • Android different resolutions problem

    - by user346665
    Hi, I have 9 (vertical) radio buttons and they are all showing in default resolution (320x480) without problems . But when I'm trying in resolution for Htc Tattoo (240x320) the last radio button is hidden - there isn't space to be shown. How to make uniformly size ?

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  • PHP problem with getimagesize()

    - by RobHardgood
    I'm using the getimagesize() function in PHP and it keeps returning an error: getimagesize(image.php?name=username&pic=picture) [function.getimagesize]: failed to open stream: No such file or directory I'm not doing anything strange with it. The only problem I can imagine is that the path URL is another PHP script that returns a page with an image header, and there is an ampersand in that URL. Here is my code: $location = "image.php?name=username&pic=picture"; $size = getimagesize($location);

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  • Checking an empty Core Data relationship (SQLite)

    - by rwat
    I have a to-many relationship in my data model, and I'd like to get all the objects that have no corresponding objects in the relationship. For example: Customer - Purchases I want to get all Customers that have 0 Purchases. I've read somewhere that I could use "Purchases[SIZE] = 0", but this gives me an unsupported function expression error, which I think means it doesn't work with a SQLite backing store (which I don't want to switch from, due to some performance constraints). Any ideas?

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  • Determining if Memory Pointer is Valid - C++

    - by Jim Fell
    It has been my observation that if free( ptr ) is called where ptr is not a valid pointer to system-allocated memory, an access violation occurs. Let's say that I call free like this: LPVOID ptr = (LPVOID)0x12345678; free( ptr ); This will most definitely cause an access violation. Is there a way to test that the memory location pointed to by ptr is valid system-allocated memory? It seems to me that the the memory management part of the Windows OS kernel must know what memory has been allocated and what memory remains for allocation. Otherwise, how could it know if enough memory remains to satisfy a given request? (rhetorical) That said, it seems reasonable to conclude that there must be a function (or set of functions) that would allow a user to determine if a pointer is valid system-allocated memory. Perhaps Microsoft has not made these functions public. If Microsoft has not provided such an API, I can only presume that it was for an intentional and specific reason. Would providing such a hook into the system prose a significant threat to system security? Situation Report Although knowing whether a memory pointer is valid could be useful in many scenarios, this is my particular situation: I am writing a driver for a new piece of hardware that is to replace an existing piece of hardware that connects to the PC via USB. My mandate is to write the new driver such that calls to the existing API for the current driver will continue to work in the PC applications in which it is used. Thus the only required changes to existing applications is to load the appropriate driver DLL(s) at startup. The problem here is that the existing driver uses a callback to send received serial messages to the application; a pointer to allocated memory containing the message is passed from the driver to the application via the callback. It is then the responsibility of the application to call another driver API to free the memory by passing back the same pointer from the application to the driver. In this scenario the second API has no way to determine if the application has actually passed back a pointer to valid memory.

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  • Prevent UIWebView sliding off the screen (iPhone)

    - by DisposableHeart
    I have a full screen UIWebView component on the screen with fixed size content, so no scrolling required. When I nudge the screen the content in moving up or down. The same effect can one experience all over the iPhone when there is a scroll-enabled component. I would like to prevent this happening in my application. Please shed some light...

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  • Responding to preference updates in Android

    - by hgpc
    I am calling a PreferenceActivity from another activity and then updating the application state (ie: changing the font size) on onActivityResult, based on the preference changes. I was thinking it would be better to put the state update logic in the PreferenceActivity. That way I don't have the duplicate the logic in each activity that calls the PreferenceActivity. What's the best or correct way to do this?

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  • Damaged data when gzipping

    - by RadiantHeart
    This is the script I hva written for gzipping content on my site, which is located in 'gzip.php'. The way i use it is that on pages where I want to enable gzipping i include the file at the top and at the bottom i call the output function like this: print_gzipped_page('javascript') If the file is a css-file i use 'css' as the $type-argument and if its a php file i call the function without declaring any arguments. The script works fine in all browsers except Opera which gives an error saying it could not decode the page due to damaged data. Can anyone tell me what I have done wrong? <?php function print_gzipped_page($type = false) { if(headers_sent()){ $encoding = false; } elseif( strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'x-gzip') !== false ){ $encoding = 'x-gzip'; } elseif( strpos($_SERVER['HTTP_ACCEPT_ENCODING'],'gzip') !== false ){ $encoding = 'gzip'; } else{ $encoding = false; } if ($type!=false) { $type_header_array = array("css" => "Content-Type: text/css", "javascript" => "Content-Type: application/x-javascript"); $type_header = $type_header_array[$type]; } $contents = ob_get_contents(); ob_end_clean(); $etag = '"' . md5($contents) . '"'; $etag_header = 'Etag: ' . $etag; header($etag_header); if ($type!=false) { header($type_header); } if (isset($_SERVER['HTTP_IF_NONE_MATCH']) and $_SERVER['HTTP_IF_NONE_MATCH']==$etag) { header("HTTP/1.1 304 Not Modified"); exit(); } if($encoding){ header('Content-Encoding: '.$encoding); print("\x1f\x8b\x08\x00\x00\x00\x00\x00"); $size = strlen($contents); $contents = gzcompress($contents, 9); $contents = substr($contents, 0, $size); } echo $contents; exit(); } ob_start(); ob_implicit_flush(0); ?> Additional info: The script works if the length og the document beeing compressed is only 10-15 characters.

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  • Open a popup window

    - by Gins
    Hi, Can i open a new window after execution of some code(ie at some point of time before completion i need to open a new window in zend.Can i do this? Also how can i check the size of a remote file. Thanks in advance.........

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  • println in grails gsp file

    - by Srinath
    I know this is simple thing, but i was not aware. I used println in gsp file and expected to print output in console. But this is showing on page. <% for(int i =0; i < threads.size();i++) { println i } % thanks.

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  • GUI programming, what to learn, already know console C++

    - by conqrr
    i have already learnt c++ console(love it!) and want to do gui programming, i have looked at Qt but i dont like the size of exe produced at all,even after compressing or static linking.... Shall i learn c# and gui programming?? is it easy to move from c++? what is dot net exactly by the way and how can it be useful to me and my CV in future??

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  • Lightest Database to be packed with an application

    - by Yatendra Goel
    I am developing a Java Desktop Application and want a light database that can be used with Hibernate and that can be packed with an application. I was going to use Derby database. It's size is near 2 MB. But before that I wanted to have views of experts on SO. Will it work with Hibernate? Actually, I am new to Hibernate and was studying that it requires a Dialect for a database so Is Hibernate has dialect for Derby?

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  • WCF: intercept message send/receive progress in client

    - by Cullen Tsering
    Hello gurus, I have a desktop application sending/receiving messages (not files) to/from a WCF service. How do I intercept the total size of the message to be transferred and receive feedback (number of bytes transferred) during the transmission so a progress bar maybe displayed to the desktop app user? How many approaches are there? What is the best one given my application scenario? Any comments or suggestions will be greatly appreciated, Cullen

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  • question about linux

    - by davit-datuashvili
    i have following question i am writting programs in linux like this from command line i do following steps touch project.java nano project.java and // code here i have questions how can i create new classes interfaces and so on?because in IDE like netbeans i can do click on projects name with right size of mouse choose create new class or interfaces and it is created but how do it in linux if i dont use IDE?

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  • What suggestions for a 3d game engine to support a huge terrain?

    - by codist
    There are a lot of 3d game engines around, does anyone with experience with them have advice on which one would likely be able to handle these (arbitrary) requirements? opengl mac/pc 1000x1000km terrain 1000 towns varying in size from 10 to 1000 buildings 128 people in any one location MMO type networking (no solo play) physics engine including airfoil c++ with optional scripting

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  • My winform application doesn't work on others' pc without vs 2010 installed

    - by wings
    Just like I said, my winform application works properly on computers with VS installed, but on other computers, it will crash due to a FileNotFound Exception. I used using Application = Microsoft.Office.Interop.Excel.Application; in my source code to generate a Excel file, and the problem occurs as soon as the Excel-related function is called. But I don't know what it refers to exactly. Do I have to get some .dll included along with the .exe file? And what DLL is that? Below are part of my codes: private void FileExport(object objTable) { StartWaiting(); string[,] table = null; try { table = (string[,])objTable; } catch (Exception ex) { ShowStatus(ex.Message, StatusType.Warning); } if (table == null) { return; } Application excelApp = new Application { DisplayAlerts = false }; Workbooks workbooks = excelApp.Workbooks; Workbook workbook = workbooks.Add(XlWBATemplate.xlWBATWorksheet); Worksheet worksheet = (Worksheet)workbook.Worksheets[1]; worksheet.Name = "TABLE"; for (int i = 0; i < table.GetLength(0); i++) { for (int j = 0; j < table.GetLength(1); j++) { worksheet.Cells[i + 1, j + 1] = table[i, j]; } } Range range = excelApp.Range["A1", "H1"]; range.Merge(); range.Font.Bold = true; range.Font.Size = 15; range.RowHeight = 50; range.EntireRow.AutoFit(); range = excelApp.Range["A2", "H8"]; range.Font.Size = 11; range = excelApp.Range["A1", "H8"]; range.NumberFormatLocal = "@"; range.RowHeight = 300; range.ColumnWidth = 50; range.HorizontalAlignment = XlHAlign.xlHAlignCenter; range.VerticalAlignment = XlVAlign.xlVAlignCenter; range.EntireRow.AutoFit(); range.EntireColumn.AutoFit(); worksheet.UsedRange.Borders.LineStyle = 1; Invoke(new MainThreadInvokerDelegate(SaveAs), new object[] { worksheet, workbook, excelApp } ); EndWaiting(); }

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  • How to invert alternate bits of a number

    - by Cupidvogel
    The problem is how to invert alternate bits of a number, starting from the LSB. Currently what I am doing is first doing a count = -1 while n: n >>= 1 count += 1 to first find the position of the leftmost set bit, then running a loop to invert every alternate bit: i = 0 while i <= count: num ^= 1<<i i += 2 Is there a quick hack solution instead of this rather boring loop solution? Of course, the solution can't make any asumption about the size of the integer.

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