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• Sending BLOBs in a JSON service,... how?

  - by Marten Sytema

  Hello I have a webservice (ie. servlet) implemented in Java. It gets some data from a MySQL table, with one column being of type BLOB (an image), and some other columns are just plain text. Normally I would store the file outside the database with a pointer to it in the database, but due to circumstance I now have to use this BLOB column... What is the proper way to send this? How to encode the image in a JSONObject, and how to parse (and RENDER!) it on the otherside ? I want to use JSONP, to avoid having to proxy it through the consumer's webserver. So that the consumer can just put in a tag pointing to the webservice, calling a callback. Any thoughts how to handle images in this situation? Also thoughts on performance etc. are interesting!

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• EXC_BAD_ACCESS when not using self.

  - by chris

  I got nabbed by the following bug again and would like some clarification to exactly why it is a bug. I have a simple UITableView that loads some data: // myclass.h @property (nonatomic, retain) NSArray *myData // myclass.m @synthesize myData; - (void) viewDidLoad { ... myData = someDataSource // note the lack of self } - (UITableViewCell *) cellForRowAtIndexPath ... { ... cell.textLabel.text = [self.myData objectAtIndex:indexPath.row]; // EXC_BAD_ACCESS } The table first loads fine, but when scrolling up enough that one of the cells is totally out of the view I then get the EXC_BAD_ACCESS error. Am I missing something in regards to @property retain. My understanding is that it releases anything that the pointer was previously pointing to before the reassignment. If I am correct then why would not using self. cause any problems? Thanks for the help.

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• Why would the assignment operator ever do something different than its matching constructor?

  - by Neil G

  I was reading some boost code, and came across this: inline sparse_vector &assign_temporary(sparse_vector &v) { swap(v); return *this; } template<class AE> inline sparse_vector &operator=(const sparse_vector<AE> &ae) { self_type temporary(ae); return assign_temporary(temporary); } It seems to be mapping all of the constructors to assignment operators. Great. But why did C++ ever opt to make them do different things? All I can think of is scoped_ptr?

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• How can I create a collection of references in C#

  - by Jonathan Kaufman

  Ok I am having a cross language hiccup. In C# with it's great collections like List and I have: a Map class with properties of: List<byte[]> Images; List<Tile> Tiles; a Tile Class of: byte[] ImageData; int X; int Y; Now I want to add an image to the Map class and have the ImageData property of the Tile Classes to "reference" it. I have discovered I can't just assign it Images[0]. You can't have a reference to an object of a List. My fix was to create a Dictionary. Is this the best way or can I somehow have a "pointer" to a collection of objects?

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• Is there a more expressive way of executing SQL query using Qt?

  - by ShaChris23

  I currently have this code: // Construct query QString const statement = QString("drop database if exists %1") .arg(databaseName_); QSqlQuery query(db); query.exec(statement); Is there a better way to code than the above? Specifically, I dont like how I use QString for SQL statement. It'd be nice if Qt has some class so that I could do something like: // Construct query QSomeClass statement = "drop database if exists %1"; statement.setArg(1, databaseName_); // Replace all %1 in the original string. QSqlQuery query(db); query.exec(statement);

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• How to unmangle exported symbols from C++ in dynamic libraries in XCode on OSX

  - by Gerald

  I've been trying to develop a dynamic library in C++ that can be run-time loaded in an application. I finally got it working, but it's a little ugly. I have a function that takes a pointer to a C++ class as an argument, which looks like this: bool registerGrindPlugin( Grind::PluginManager* mgr ); But of course it's being exported as: _Z19registerGrindPluginPN5Grind13PluginManagerE I tried a .c file with a simple function and it exported fine as "registerGrindPlugin", but of course I can't pass a C++ class as the argument that way. Soo... my question is, is there a way to unmangle or alias the exported symbol so that I don't have to use a monstrosity like Z19registerGrindPluginPN5Grind13PluginManagerE in my dlsym call? I did see something about -alias_list as a linker option, but I haven't quite figured out how to use it in XCode. If that is the solution, can somebody provide some more details on how to use this?

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• SDL_BlitSurface() not displaying image?

  - by Christian Gonzalez

  So I'm trying to display a simply image with the SDL library, but when I use the function SDL_BlitSurface() nothing happens, and all I get is a black screen. I should also note that I have the .bmp file, the source, and the executable file all in the same directory. //SDL Header #include "SDL/SDL.h" int main(int argc, char* args[]) { //Starts SDL SDL_Init(SDL_INIT_EVERYTHING); //SDL Surfaces are images that are going to be displayed. SDL_Surface* Hello = NULL; SDL_Surface* Screen = NULL; //Sets the size of the window (Length, Height, Color(bits), Sets the Surface in Software Memory) Screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE); //Loads a .bmp image Hello = SDL_LoadBMP("Hello.bmp"); //Applies the loaded image to the screen SDL_BlitSurface(Hello, NULL, Screen, NULL); //Update Screen SDL_Flip(Screen); //Pause SDL_Delay(2000); //Deletes the loaded image from memory SDL_FreeSurface(Hello); //Quits SDL SDL_Quit(); return 0; }

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• C++ Memory Allocation & Linked List Implementation

  - by pws5068

  I'm writing software to simulate the "first-fit" memory allocation schema. Basically, I allocate a large X megabyte chunk of memory and subdivide it into blocks when chunks are requested according to the schema. I'm using a linked list called "node" as a header for each block of memory (so that we can find the next block without tediously looping through every address value. head_ptr = (char*) malloc(total_size + sizeof(node)); if(head_ptr == NULL) return -1; // Malloc Error .. :-( node* head_node = new node; // Build block header head_node->next = NULL; head_node->previous = NULL; // Header points to next block (which doesn't exist yet) memset(head_ptr,head_node, sizeof(node)); ` But this last line returns: error: invalid conversion from 'node*' to 'int' I understand why this is invalid.. but how can I place my node into the pointer location of my newly allocated memory?

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• Conseqences of assigning self

  - by Vegar

  Hi, Found a piece of code today, that I find a little smelly... TMyObject.LoadFromFile(const filename: String); begin if fileExists(filename) then self := TSomeObjectStreamer.ReadObjectFromFile(filename); end; If this code works, it will atleast leak some memory, but does it work? Is OK to assign to self in this manner? What if the streamed object is of a different subclass then the original self? What if the streamed object is of a different class with no common ancestore to the original self?

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• Performance intensive string splitting and manipulation in java

  - by juhanic

  What is the most efficient way to split a string by a very simple separator? Some background: I am porting a function I wrote in C with a bunch of pointer arithmetic to java and it is incredibly slow(After some optimisation still 5* slower). Having profiled it, it turns out a lot of that overhead is in String.split The function in question takes a host name or ip address and makes it generic: 123.123.123.123-*.123.123.123 a.b.c.example.com-*.example.com This can be run over several million items on a regular basis, so performance is an issue.

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• Struct size containing vector<T> different sizes between DLL and EXE..

  - by Michael Peddicord

  I have this situation where an EXE program imports a DLL for a single function call. It works by passing in a custom structure and returning a different custom structure. Up till now it's worked fine until I wanted one of the structs data members to be a vector < MyStruct When I do a sizeof(vector< MyStruct ) in my program I get a size of 20 but when I do it from inside the DLL I get a size of 24. This size inconsistency is causing a ESP pointer error. Can anyone tell me why a Vector < MyStruct would be a different size in the DLL than in the program? I have reverified that my structs in both the DLL and the Program are identical. I would appreciate any help on the subject. Thank you.

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• addObjectsFromArray

  - by derek.lo

  I have a question about memory management when using the addObjectsFromArray method. Basically, I have 2 arrays defined in the appDelegate. I need these 2 arrays for the duration of my application's runtime. I therefore release them in my appDelegate's dealloc method. When I go to use these two arrays in a class, I want one array to store the values from the other, so that the other can have it's contents removed, but still stick around for use. Something like this: [appDelegate.arrayTwo addObjectsFromArray:appDelegate.arrayOne]; [appDelegate.arrayOne removeAllObjects]; I'm getting the compiler error: EXC_BAD_ACCESS because of a pointer issue? retaining issue? Any help would be greatly appreciated! Thanks

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• Compilation Error on Recursive Variadic Template Function

  - by Maxpm

  I've prepared a simple variadic template test in Code::Blocks, but I'm getting an error: No matching function for call to 'OutputSizes()' Here's my source code: #include <iostream> #include <typeinfo> using namespace std; template <typename FirstDatatype, typename... DatatypeList> void OutputSizes() { std::cout << typeid(FirstDatatype).name() << ": " << sizeof(FirstDatatype) << std::endl; OutputSizes<DatatypeList...>(); } int main() { OutputSizes<char, int, long int>(); return 0; } I'm using GNU GCC with -std=C++0x. Using std=gnu++0x makes no difference.

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• How do you write byte[] array using log4.net

  - by like.no.other

  Hi, I have a byte[] with some data in it, I would like to write this byte array AS-IS to the log file using log4.net. The problems that i am facing is that There are no overload for byte[] in TextWriter, so even implementing an IObjectRenderer is of no use. I dont have access to the underlying Stream object of Log4.net Also tried converting byte[] into char[] still when i write it, it adds an extra byte. Is this even possible with Log4.net. Thanx in Advance.

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• Fast read of certain bytes of multiple files in C/C++

  - by Alejandro Cámara

  I've been searching in the web about this question and although there are many similar questions about read/write in C/C++, I haven't found about this specific task. I want to be able to read from multiple files (256x256 files) only sizeof(double) bytes located in a certain position of each file. Right now my solution is, for each file: Open the file (read, binary mode): fstream fTest("current_file", ios_base::out | ios_base::binary); Seek the position I want to read: fTest.seekg(position*sizeof(test_value), ios_base::beg); Read the bytes: fTest.read((char *) &(output[i][j]), sizeof(test_value)); And close the file: fTest.close(); This takes about 350 ms to run inside a for{ for {} } structure with 256x256 iterations (one for each file). Q: Do you think there is a better way to implement this operation? How would you do it?

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• Unable to create unmanaged object using new keyword in managed C++

  - by chair79

  Hi all, I've created a class with a boost::unordered_map as a member, Linkage.h #ifndef LINKAGE_H #define LINKAGE_H #include <boost/unordered_map.hpp> class Linkage { private: boost::unordered_map<int, int> m_IOMap; public: .... }; Linkage.cpp #include "stdafx.h" ... // methods and in the managed side of C++, I try to create the pointer of the obj: private: System::Void Form1_Load(System::Object^ sender, System::EventArgs^ e) { Linkage* m_pLink = new Linkage(); ..... } However this produces errors: Error 4 error LNK2005: "private: static unsigned int const boost::detail::type_with_alignment_imp<4>::found" (?found@?$type_with_alignment_imp@$03@detail@boost@@$$Q0IB) already defined in Proj_Test.obj Linkage.obj ..... Error 7 fatal error LNK1169: one or more multiply defined symbols found Could anyone explain to me pls? Thanks.

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• Jquery clickable block

  - by Clint

  HI, I have this code for extracting the href and adding it to a parent block... $(".new-dev").hover(function(){ $(this).css('cursor','pointer'); $('this').$('a').css('color','#696969'); },function(){ $('this').$('a').css('color','#000'); }); What I want to do is make the a within the block change color on rollover. Unsure of how to do this when using $(this). Any advice welcome. Thanks, C

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• MySQL Rank Not Matching High Score in Table

  - by boddie

  While making a game the MySQL call to get the top 10 is as follows: SELECT username, score FROM userinfo ORDER BY score DESC LIMIT 10 This seems to work decently enough, but when paired with a call to get a individual player's rank the numbers may be different if the player has a tied score with other players. The call to get the players rank is as follows: SELECT (SELECT COUNT(*) FROM userinfo ui WHERE (ui.score, ui.username) >= (uo.score, uo.username)) AS rank FROM userinfo uo WHERE username='boddie'; Example results from first call: +------------+-------+ | username | score | +------------+-------+ | admin | 4878 | | test3 | 3456 | | char | 785 | | test2 | 456 | | test1 | 253 | | test4 | 78 | | test7 | 0 | | boddie | 0 | | Lz | 0 | | char1 | 0 | +------------+-------+ Example results from second call +------+ | rank | +------+ | 10 | +------+ As can be seen, the first call ranks the player at number 8 on the list, but the second call puts him at number 10. What changes or what can I do to make these calls give matching results? Thank you in advance for any help!

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• Process for linking static ObjC libraries in XCode

  - by madmik3

  I'm trying to link to a static library and I keep getting linker errors. I've found a few sites that post examples but I have not been able to see what I am doing wrong. First I create a project that will link to my lib add existing files find my .xcodeproj file select "Copy items into destination groups folder"... Select my host project as Add To Targets. Then I add a direct dependency to my host app expand targets double click MyHost.app click + under direct dependencies select my lib Then I set build flags double click MyHost application icon in Groups and Files. click the build tab then I set the OtherLinerFlag to -ObjC then I set Header Search Paths to my header file location for my static library. I pass the compile stage but any classes in my static lib cause linker error: literal-pointer@_OBJC@_cls_refs@SomeClass in MyHost.o thanks!

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• How to ensure that no non-ascii unicode characters are entered ?

  - by Jacques René Mesrine

  Given a java.lang.String instance, I want to verify that it doesn't contain any unicode characters that are not ASCII alphanumerics. e.g. The string should be limited to [A-Za-z0-9.]. What I'm doing now is something very inefficient: import org.apache.commons.lang.CharUtils; String s = ...; char[] ch = s.toCharArray(); for( int i=0; i<ch.length; i++) { if( ! CharUtils.isAsciiAlphanumeric( ch[ i ] ) throw new InvalidInput( ch[i] + " is invalid" ); } Is there a better way to solve this ?

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• HierarchicalDataTemplate Link By Parent

  - by Andrew Kalashnikov

  Hello colleagues. I want bind my treeview. There are a lot of samples binding treeview by object, which contains children collection. I've got domain having just Parent pointer. public class Service : BaseDomain { public virtual string Name { get; set; } public virtual string Description { get; set; } public virtual Service Parent { get; set; } } Can I bind collection of this objects to my treeView. Thanks

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• Advanced LINQ Update Statement

  - by user1902490

  I have a data base with Price_old like: Date --- Hour --- Price _____________________________ Jan 1 --- 1 --- $3.0 Jan 1 --- 2 --- $3.1 Jan 1 --- 3 --- $3.3 Jan 1 --- 4 --- $3.15 Jan 2 --- 1 --- $2.95 Jan 2 --- 2 --- $3.2 Jan 2 --- 3 --- $3.05 What I then have is a spreadsheet, with the same structure, that I will be reading into a datatable, I'll call the new datatable Price_New, note that price new may not have all the same date/hours as Price_Old So, I end up with 2 datatables, Price_Old, and Price_New, and what I need to do is update Price_old with the new prices in Price_New, and then commit those new prices to the Database. I am kinda new to LINQ (about 30 mins of experience) and would really appreciate if someone could give me a pointer or two on whether or not this is doing in LINQ and what the best method would be. Thanks

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• Does replacing statements by expressions using the C++ comma operator could allow more compiler opti

  - by Gabriel Cuvillier

  The C++ comma operator is used to chain individual expressions, yielding the value of the last executed expression as the result. For example the skeleton code (6 statements, 6 expressions): step1; step2; if (condition) step3; return step4; else return step5; May be rewritten to: (1 statement, 6 expressions) return step1, step2, condition? step3, step4 : step5; I noticed that it is not possible to perform step-by-step debugging of such code, as the expression chain seems to be executed as a whole. Does it means that the compiler is able to perform special optimizations which are not possible with the traditional statement approach (specially if the steps are const or inline)? Note: I'm not talking about the coding style merit of that way of expressing sequence of expressions! Just about the possible optimisations allowed by replacing statements by expressions.

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• IE error with jquery counter plugin

  - by Mankey

  I've implemented a jquery counter script (count up from say 50 to 100 with different increments) that I found from this question: jQuery counter to count up to a target number The scripts works great except for in Internet Explorer 8 (and possibly other IE versions?). Here's an error message from IE with the URL to the creator of the script's demo. Message: 'undefined' is null or not an object Line: 32 Char: 17 Code: 0 URI: http://www.ulmanen.fi/stuff/counter.php I'm just wondering if anyone know how this can be fixed. I'm guessing it has to do with el.html() not finding any data but I can't really figure this out. Thanks for any help ^^ I would reply to that post if I could but I can't seem to find any way of doing so (I'm new to stackoverflow, I think I lack privileges).

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• IO completion port key confusion

  - by Richard Tew

  I'm writing an IO completion port based server (source code here) using the Windows DLL API in Python using the ctypes module. But this is a pretty direct usage of the API and this question is directed at those who have a knowledge of IOCP, not Python. As I understand the documentation for CreateIoCompletionPort, you specify your "user defined" completion key when you call this function with a file handle (in my case a socket) you are associating with the created IOCP. When you get around to calling GetQueuedCompletionStatus, you get a completion key value along with a pointer to an overlapped object. The completion key should identify what overlapped object and request has completed. However, let's say I pass in 100 as the completion key in my CreateIoCompletionPort call with an overlapped object. When the same overlapped object has its IO completed and it arrives back through GetQueuedCompletionStatus, the completion key that accompanies it is much larger and bares no resemblance to the original value of 100. Am I misunderstanding how the completion key works, or must I be doing it wrong in the source code I linked above?

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