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  • boost.asio error on read from socket.

    - by niXman
    The following code of the client: typedef boost::array<char, 10> header_packet; header_packet header; boost::system::error_code error; ... /** send header */ boost::asio::write( _socket, boost::asio::buffer(header, header.size()), boost::asio::transfer_all(), error ); /** send body */ boost::asio::write( _socket, boost::asio::buffer(buffer, buffer.length()), boost::asio::transfer_all(), error ); of the server: struct header { boost::uint32_t header_length; boost::uint32_t id; boost::uint32_t body_length; }; static header unpack_header(const header_packet& data) { header hdr; sscanf(data.data(), "%02d%04d%04d", &hdr.header_length, &hdr.id, &hdr.body_length); return hdr; } void connection::start() { boost::asio::async_read( _socket, boost::asio::buffer(_header, _header.size()), boost::bind( &connection::read_header_handler, shared_from_this(), boost::asio::placeholders::error ) ); } /***************************************************************************/ void connection::read_header_handler(const boost::system::error_code& e) { if ( !e ) { std::cout << "readed header: " << _header.c_array() << std::endl; std::cout << constants::unpack_header(_header); boost::asio::async_read( _socket, boost::asio::buffer(_body, constants::unpack_header(_header).body_length), boost::bind( &connection::read_body_handler, shared_from_this(), boost::asio::placeholders::error ) ); } else { /** report error */ std::cout << "read header finished with error: " << e.message() << std::endl; } } /***************************************************************************/ void connection::read_body_handler(const boost::system::error_code& e) { if ( !e ) { std::cout << "readed body: " << _body.c_array() << std::endl; start(); } else { /** report error */ std::cout << "read body finished with error: " << e.message() << std::endl; } } On the server side the method read_header_handler() is called, but the method read_body_handler() is never called. Though the client has written down the data in a socket. The header is readed and decoded successfully. What's the error?

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  • How can two threads access a common array of buffers with minimal blocking ? (c#)

    - by Jelly Amma
    Hello, I'm working on an image processing application where I have two threads on top of my main thread: 1 - CameraThread that captures images from the webcam and writes them into a buffer 2 - ImageProcessingThread that takes the latest image from that buffer for filtering. The reason why this is multithreaded is because speed is critical and I need to have CameraThread to keep grabbing pictures and making the latest capture ready to pick up by ImageProcessingThread while it's still processing the previous image. My problem is about finding a fast and thread-safe way to access that common buffer and I've figured that, ideally, it should be a triple buffer (image[3]) so that if ImageProcessingThread is slow, then CameraThread can keep on writing on the two other images and vice versa. What sort of locking mechanism would be the most appropriate for this to be thread-safe ? I looked at the lock statement but it seems like it would make a thread block-waiting for another one to be finished and that would be against the point of triple buffering. Thanks in advance for any idea or advice. J.

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  • zlib gzgets extremely slow?

    - by monkeyking
    I'm doing stuff related to parsing huge globs of textfiles, and was testing what input method to use. There is not much of a difference using c++ std::ifstreams vs c FILE, According to the documentation of zlib, it supports uncompressed files, and will read the file without decompression. I'm seeing a difference from 12 seconds using non zlib to more than 4 minutes using zlib.h This I've tested doing multiple runs, so its not a disk cache issue. Am I using zlib in some wrong way? thanks #include <zlib.h> #include <cstdio> #include <cstdlib> #include <fstream> #define LENS 1000000 size_t fg(const char *fname){ fprintf(stderr,"\t-> using fgets\n"); FILE *fp =fopen(fname,"r"); size_t nLines =0; char *buffer = new char[LENS]; while(NULL!=fgets(buffer,LENS,fp)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } size_t is(const char *fname){ fprintf(stderr,"\t-> using ifstream\n"); std::ifstream is(fname,std::ios::in); size_t nLines =0; char *buffer = new char[LENS]; while(is. getline(buffer,LENS)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } size_t iz(const char *fname){ fprintf(stderr,"\t-> using zlib\n"); gzFile fp =gzopen(fname,"r"); size_t nLines =0; char *buffer = new char[LENS]; while(0!=gzgets(fp,buffer,LENS)) nLines++; fprintf(stderr,"%lu\n",nLines); return nLines; } int main(int argc,char**argv){ if(atoi(argv[2])==0) fg(argv[1]); if(atoi(argv[2])==1) is(argv[1]); if(atoi(argv[2])==2) iz(argv[1]); }

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  • Progressively stream the output of an ASP.NET page - or render a page outside of an HTTP request

    - by Evgeny
    I have an ASP.NET 2.0 page with many repeating blocks, including a third-party server-side control (so it's not just plain HTML). Each is quite expensive to generate, in terms of both CPU and RAM. I'm currently using a standard Repeater control for this. There are two problems with this simple approach: The entire page must be rendered before any of it is returned to the client, so the user must wait a long time before they see any data. (I write progress messages using Response.Write, so there is feedback, but no actual results.) The ASP.NET worker process must hold everything in memory at the same time. There is no inherent needs for this: once one block is processed it won't be changed, so it could be returned to the client and the memory could be freed. I would like to somehow return these blocks to the client one at a time, as each is generated. I'm thinking of extracting the stuff inside the Repeater into a separate page and getting it repeatedly using AJAX, but there are some complications involved in that and I wonder if there is some simper approach. Ideally I'd like to keep it as one page (from the client's point of view), but return it incrementally. Another way would be to do something similar, but on the server: still create a separate page, but have the server access it and then Response.Write() the HTML it gets to the response stream for the real client request. Is there a way to avoid an HTTP request here, though? Is there some ASP.NET method that would render a UserControl or a Page outside of an HTTP request and simply return the HTML to me as a string? I'm open to other ideas on how to do this as well.

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  • How do you send a named pipe string from umnanaged to managed code space?

    - by billmcf
    I appear to have a named pipes 101 issue. I have a very simple set up to connect a simplex named pipe transmitting from a C++ unmanaged app to a C# managed app. The pipe connects, but I cannot send a "message" through the pipe unless I close the handle which appears to flush the buffer and pass the message through. It's like the message is blocked. I have tried reversing the roles of client/server and invoking them with different Flag combinations without any luck. I can easily send messages in the other direction from C# managed to C++ unmanaged. Does anyone have any insight. Can any of you guys successfully send messages from C++ unmanaged to C# managed? I can find plenty of examples of intra amanged or unmanaged pipes but not inter managed to/from unamanged - just claims to be able to do it. In the listings, I have omitted much of the wrapper stuff for clarity. The key bits I believe that are relevant are the pipe connection/creation/read and write methods. Don't worry too much about blocking/threading here. C# Server side // This runs in its own thread and so it is OK to block private void ConnectToClient() { // This server will listen to the sending client if (m_InPipeStream == null) { m_InPipeStream = new NamedPipeServerStream("TestPipe", PipeDirection.In, 1); } // Wait for client to connect to our server m_InPipeStream.WaitForConnection(); // Verify client is running if (!m_InPipeStream.IsConnected) { return; } // Start listening for messages on the client stream if (m_InPipeStream != null && m_InPipeStream.CanRead) { ReadThread = new Thread(new ParameterizedThreadStart(Read)); ReadThread.Start(m_InPipeStream); } } // This runs in its own thread and so it is OK to block private void Read(object serverObj) { NamedPipeServerStream pipeStream = (NamedPipeServerStream)serverObj; using (StreamReader sr = new StreamReader(pipeStream)) { while (true) { string buffer = "" ; try { // Blocks here until the handle is closed by the client-side!! buffer = sr.ReadLine(); // <<<<<<<<<<<<<< Sticks here } catch { // Read error break; } // Client has disconnected? if (buffer == null || buffer.Length == 0) break; // Fire message received event if message is non-empty if (MessageReceived != null && buffer != "") { MessageReceived(buffer); } } } } C++ client side // Static - running in its own thread. DWORD CNamedPipe::ListenForServer(LPVOID arg) { // The calling app (this) is passed as the parameter CNamedPipe* app = (CNamedPipe*)arg; // Out-Pipe: connect as a client to a waiting server app->m_hOutPipeHandle = CreateFile("\\\\.\\pipe\\TestPipe", GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL); // Could not create handle if (app->m_hInPipeHandle == NULL || app->m_hInPipeHandle == INVALID_HANDLE_VALUE) { return 1; } return 0; } // Sends a message to the server BOOL CNamedPipe::SendMessage(CString message) { DWORD dwSent; if (m_hOutPipeHandle == NULL || m_hOutPipeHandle == INVALID_HANDLE_VALUE) { return FALSE; } else { BOOL bOK = WriteFile(m_hOutPipeHandle, message, message.GetLength()+1, &dwSent, NULL); //FlushFileBuffers(m_hOutPipeHandle); // <<<<<<< Tried this return (!bOK || (message.GetLength()+1) != dwSent) ? FALSE : TRUE; } } // Somewhere in the Windows C++/MFC code... ... // This write is non-blocking. It just passes through having loaded the pipe. m_pNamedPipe->SendMessage("Hi de hi"); ...

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  • char[] and char* compatibility?

    - by Aerovistae
    In essence, will this code work? And before you say "Run it and see!", I just realized my cygwin didn't come with gcc and it's currently 40 minutes away from completing reinstallation. That being said: char* words[1000]; for(int i = 0; i<1000; i++) words[i] = NULL; char buffer[ 1024 ]; //omit code that places "ADD splash\0" into the buffer if(strncmp (buffer, "ADD ", 4){ char* temp = buffer + 4; printf("Adding: %s", temp); int i = 0; while(words[i] != NULL) i++; words[i] = temp; } I'm mostly uncertain about the line char* temp = buffer + 4, and also whether I can assign words[i] in the manner that I am. Am I going to get type errors when I eventually try to compile this in 40 minutes? Also-- if this works, why don't I need to use malloc() on each element of words[]? Why can I say words[i] = temp, instead of needing to allocate memory for words[i] the length of temp?

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  • Same IL code, different output - how is it possible?

    - by Hali
    When I compile this code with mono (gmcs) and run it, it outputs -1 (both with mono and .Net framework). When I compile it with VS (csc), it outputs -1 when I run it with mono, and 0 when I run it with the .Net framework. The code in question is: using System; public class Program { public static void Main() { Console.WriteLine(string.Compare("alo\0alo\0", "alo\0alo\0\0", false, System.Globalization.CultureInfo.InvariantCulture)); } } Compiled with VS: .method public hidebysig static void Main() cil managed { .entrypoint // Code size 29 (0x1d) .maxstack 8 IL_0000: nop IL_0001: ldstr bytearray (61 00 6C 00 6F 00 00 00 61 00 6C 00 6F 00 00 00 ) // a.l.o...a.l.o... IL_0006: ldstr bytearray (61 00 6C 00 6F 00 00 00 61 00 6C 00 6F 00 00 00 // a.l.o...a.l.o... 00 00 ) IL_000b: ldc.i4.0 IL_000c: call class [mscorlib]System.Globalization.CultureInfo [mscorlib]System.Globalization.CultureInfo::get_InvariantCulture() IL_0011: call int32 [mscorlib]System.String::Compare(string, string, bool, class [mscorlib]System.Globalization.CultureInfo) IL_0016: call void [mscorlib]System.Console::WriteLine(int32) IL_001b: nop IL_001c: ret } // end of method Program::Main Compiled with mono: .method public hidebysig static void Main() cil managed { .entrypoint // Code size 27 (0x1b) .maxstack 8 IL_0000: ldstr bytearray (61 00 6C 00 6F 00 00 00 61 00 6C 00 6F 00 00 00 ) // a.l.o...a.l.o... IL_0005: ldstr bytearray (61 00 6C 00 6F 00 00 00 61 00 6C 00 6F 00 00 00 // a.l.o...a.l.o... 00 00 ) IL_000a: ldc.i4.0 IL_000b: call class [mscorlib]System.Globalization.CultureInfo [mscorlib]System.Globalization.CultureInfo::get_InvariantCulture() IL_0010: call int32 [mscorlib]System.String::Compare(string, string, bool, class [mscorlib]System.Globalization.CultureInfo) IL_0015: call void [mscorlib]System.Console::WriteLine(int32) IL_001a: ret } // end of method Program::Main The only difference is the two extra NOP instructions in the VS version. How is it possible?

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  • Why isn't my log4net appender buffering?

    - by Eric
    I've created a custom log4net appender. It descends from log4net.Appender.SmtpAppender which descends from log4net.Appender.BufferingAppenderSkeleton. I programatically setup the following parameters in its constructor: this.Lossy = false; //don't drop any messages this.BufferSize = 3; //buffer up to 3 messages this.Threshold = log4net.Core.Level.Error; //append messages of Error or higher this.Evaluator = new log4net.Core.LevelEvaluator(Level.Off); //don't flush the buffer for any message, regardless of level I expect this would buffer 3 events of level Error or higher and deliver those events when the buffer is filled. However, I'm finding that the events are not buffered at all; instead, SendBuffer() is called immediately every time an error is logged. Is there a mistake in my configuration? Thanks

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  • show output of file on client side using jquery + javascript .

    - by tazimk
    Hi, Written some code in my view function : This code reads a file from server . stores it in a list .passes to client def showfiledata(request): f = open("/home/tazim/webexample/test.txt") list = f.readlines() return_dict = {'list':list} json = simplejson.dumps(list) return HttpResponse(json,mimetype="application/json") On, client side the $.ajax callback function receives this list of lines. Now, My Question is . I have to display these lines in a textarea. But these lines should not be displayed at once . Each line should be appended in textarea with some delay. (Use of setInterval is required as per my knowledge) . Also I am using jquery in my templates. The server used is Django . Please provide some solution as in some sample code will be quite helpful .

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  • Bash: Is it ok to use same input file as output of a piped command?

    - by Amro
    Consider something like: cat file | command > file Is this good practice? Could this overwrite the input file as the same time as we are reading it, or is it always read first in memory then piped to second command? Obviously I can use temp files as intermediary step, but I'm just wondering.. t=$(mktemp) cat file | command > ${t} && mv ${t} file

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  • Why in the following code the output is different when I compile or run it more than once

    - by Sanjeev
    class Name implements Runnable { public void run() { for (int x = 1; x <= 3; x++) { System.out.println("Run by " + Thread.currentThread().getName() + ", x is " + x); } } } public class Threadtest { public static void main(String [] args) { // Make one Runnable Name nr = new Name(); Thread one = new Thread(nr); Thread two = new Thread(nr); Thread three = new Thread(nr); one.setName("A"); two.setName("B"); three.setName("C"); one.start(); two.start(); three.start(); } } The answer is different while compiling and running more then one time I don't know why? any idea.

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  • How do I output the preorder traversal of a tree given the inorder and postorder tranversal?

    - by user342580
    Given the code for outputing the postorder traversal of a tree when I have the preorder and the inorder traversal in an interger array. How do I similarily get the preorder with the inorder and postorder array given? void postorder( int preorder[], int prestart, int inorder[], int inostart, int length) { if(length==0) return; //terminating condition int i; for(i=inostart; i<inostart+length; i++) if(preorder[prestart]==inorder[i])//break when found root in inorder array break; postorder(preorder, prestart+1, inorder, inostart, i-inostart); postorder(preorder, prestart+i-inostart+1, inorder, i+1, length-i+inostart-1); cout<<preorder[prestart]<<" "; } Here is the prototype for preorder() void preorder( int inorderorder[], int inostart, int postorder[], int poststart, int length)

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  • MySQL Query, limit output display according/only to associated ID!

    - by Jess
    So here's my situation. I have a books table and authors table. An author can have many books... In my authors page view, the user (logged in) can click an author in a tabled row and be directed to a page displaying the author's books (collected like this URI format: viewauthorbooks.php?author_id=23), very straight forward... However, in my query, I need to display the books for the author only, and not all books stored in the books table (as i currently have!) As I am a complete novice, I used the most simple query of: SELECT * FROM tasks_tb :)....this returns the books for me, but returns every single value (book) in the database, and not ones associated with the selected author. And when I click a different author the same books are displayed for them...I think everyone gets what I'm trying to achieve, I just don't know how to perform the query. I'm guessing that I need to start using more advanced query clauses like INNER JOIN etc. Anyone care to help me out :)

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  • Is the C++ compiler optimizer allowed to break my destructor ability to be called multiple times?

    - by sharptooth
    We once had an interview with a very experienced C++ developer who couldn't answer the following question: is it necessary to call the base class destructor from the derived class destructor in C++? Obviously the answer is no, C++ will call the base class destructor automagically anyway. But what if we attempt to do the call? As I see it the result will depend on whether the base class destructor can be called twice without invoking erroneous behavior. For example in this case: class BaseSafe { public: ~BaseSafe() { } private: int data; }; class DerivedSafe { public: ~DerivedSafe() { BaseSafe::~BaseSafe(); } }; everything will be fine - the BaseSafe destructor can be called twice safely and the program will run allright. But in this case: class BaseUnsafe { public: BaseUnsafe() { buffer = new char[100]; } ~BaseUnsafe () { delete[] buffer; } private: char* buffer; }; class DerivedUnsafe { public: ~DerivedUnsafe () { BaseUnsafe::~BaseUnsafe(); } }; the explicic call will run fine, but then the implicit (automagic) call to the destructor will trigger double-delete and undefined behavior. Looks like it is easy to avoid the UB in the second case. Just set buffer to null pointer after delete[]. But will this help? I mean the destructor is expected to only be run once on a fully constructed object, so the optimizer could decide that setting buffer to null pointer makes no sense and eliminate that code exposing the program to double-delete. Is the compiler allowed to do that?

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  • Stored procedure with output parameters vs. table-valued function?

    - by abatishchev
    Which approach is better to use if I need a member (sp or func) returning 2 parameters: CREATE PROCEDURE Test @in INT, @outID INT OUT, @amount DECIMAL OUT AS BEGIN ... END or CREATE FUNCTION Test ( @in INT ) RETURNS @ret TABLE (outID INT, amount DECIMAL) AS BEGIN ... END What are pros and cons of each approach considering that the result will passed to another stored procedure: EXEC Foobar @outID, @outAmount

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  • What happens when we say "listen to a port" ?

    - by smwikipedia
    Hi, When we start a server application, we always need to speicify the port number it listens to. But how is this "listening mechanism" implemented under the hood? My current imagination is like this: The operating system associate the port number with some buffer. The server application's responsibiligy is to monitor this buffer. If there's no data in this buffer, the server application's listen operation will just block the application. When some data arrives from the wire, the operating system will know that check the data and see if it is targed at this port number. And then it will fill the buffer. And then OS will notify the blocked server application and the server application will get the data and continue to run. Question is: If the above scenario is correct, how could the opearting system know there's data arriving from wire? It cannot be a busy pooling. Is it some kind of interrupt-based mechanism? If there's too much data arriving and the buffer is not big enough, will there be data loss? Is the "listen to a port" operation really a blocking operation? Many thanks.

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  • Preallocating memory with C++ in realtime environment

    - by Elazar Leibovich
    I'm having a function which gets an input buffer of n bytes, and needs an auxillary buffer of n bytes in order to process the given input buffer. (I know vector is allocating memory at runtime, let's say that I'm using a vector which uses static preallocated memory. Imagine this is NOT an STL vector.) The usual approach is void processData(vector<T> &vec) { vector<T> &aux = new vector<T>(vec.size()); //dynamically allocate memory // process data } //usage: processData(v) Since I'm working in a real time environment, I wish to preallocate all the memory I'll ever need in advance. The buffer is allocated only once at startup. I want that whenever I'm allocating a vector, I'll automatically allocate auxillary buffer for my processData function. I can do something similar with a template function static void _processData(vector<T> &vec,vector<T> &aux) { // process data } template<size_t sz> void processData(vector<T> &vec) { static aux_buffer[sz]; vector aux(vec.size(),aux_buffer); // use aux_buffer for the vector _processData(vec,aux); } // usage: processData<V_MAX_SIZE>(v); However working alot with templates is not much fun (now let's recompile everything since I changed a comment!), and it forces me to do some bookkeeping whenever I use this function. Are there any nicer designs around this problem?

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  • wxPython - How can I display a html formatted string in wx.RichTextCtrl

    - by wxpydon
    Hello, I'm trying to display some string (html formatted) in a Richtext Ctrl. In my code I tried to use it this way (self.txtmain is the RichTextCtrl): out = StringIO() htmlhandler = rt.RichTextHTMLHandler() buffer = self.txtmain.GetBuffer() buffer.AddHandler(htmlhandler) out.write(string) out.seek(0) htmlhandler.LoadStream(buffer, out) self.txtmain.Refresh() No errors are issued, but the RichTextCtrl windows is not updated. What am I missing here?

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  • Real Time Sound Captureing J2ME

    - by Abdul jalil
    i am capturing sound in J2me and send these bytes to remote system, i then play these bytes on remote system.five second voice is capture and send to remote system. i get the repeated sound again .i am making a sound messenger please help me where i am doing wrong i am using the follown code . String remoteTimeServerAddress="192.168.137.179"; sc = (SocketConnection) Connector.open("socket://"+remoteTimeServerAddress+":13"); p = Manager.createPlayer("capture://audio?encoding=pcm&rate=11025&bits=16&channels=1"); p.realize(); RecordControl rc = (RecordControl)p.getControl("RecordControl"); ByteArrayOutputStream output = new ByteArrayOutputStream(); OutputStream outstream =sc.openOutputStream(); rc.setRecordStream(output); rc.startRecord(); p.start(); int size=output.size(); int offset=0; while(true) { Thread.currentThread().sleep(5000); rc.commit(); output.flush(); size=output.size(); if(size0) { recordedSoundArray=output.toByteArray(); outstream.write(recordedSoundArray,0,size); } output.reset(); rc.reset(); rc.setRecordStream(output); rc.startRecord(); }

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  • get content from website with utf8 format

    - by zahir
    i want how to get the content from websites with utf8 format,, i have writing the following code is try { String webnames = "http://pathivu.com"; URL url = new URL(webnames); URLConnection urlc = url.openConnection(); //BufferedInputStream buffer = new BufferedInputStream(urlc.getInputStream()); BufferedReader buffer = new BufferedReader(new InputStreamReader(urlc.getInputStream(), "UTF8")); StringBuilder builder = new StringBuilder(); int byteRead; while ((byteRead = buffer.read()) != -1) builder.append((char) byteRead); buffer.close(); String text=builder.toString(); System.out.println(text); } catch (IOException e) { e.printStackTrace(); } but i cant get the correct format... thanks and advance..

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  • Why is C++ fwrite() producing larger output in release?

    - by waffleShirt
    I recently wrote an implementation of the Canonical Huffman compression algorithm. I have a 500kb test file that can be compressed to about 250kb when running the debug and release builds from within Visual Studio 2008. However when I run the release build straight from the executeable the test file only compresses to about 330kb. I am assuming that something is going wrong when the file is written using fwrite(). I have tested the program and confirmed that uncompressing the files always produces the correct uncompressed file. Does anyone know why this could possibly be? How could the same executeable file be producing different sized outputs based on where it is launched from?

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