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  • How to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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  • how to use XML sent by html form?

    - by user32167
    i have html form with textarea in which i paste some XML, for example: <network ip_addr="10.0.0.0/8" save_ip="true"> <subnet interf_used="200" name="lan1" /> <subnet interf_used="254" name="lan2" /> </network> When user submit form, that data is send to Java server, so in headers i get something like that: GET /?we=%3Cnetwork+ip_addr%3D%2210.0.0.0%2F8%22+save_ip%3D%22true%22%3E%0D%0A%3Csubnet+interf_used%3D%22200%22+name%3D%22lan1%22+%2F%3E%0D%0A%3Csubnet+interf_used%3D%22254%22+name%3D%22lan2%22+%2F%3E%0D%0A%3C%2Fnetwork%3E HTTP/1.1 how can i use that in my Java applications? I need to make some calculations on that data and re-send new generated XML.

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  • How do I setup a Python development environment on Linux ?

    - by Rob Sobers
    I'm a .NET developer who knows very little about Python, but want to give it a test drive for a small project I'm working on. What tools and packages should I install on my machine? I'm looking for a common, somewhat comprehensive, development environment. I'll likely run Ubuntu 9.10, but I'm flexible. If Windows is a better option, that's fine too.

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  • 0xDEADBEEF equivalent for 64-bit development?

    - by Peter Mortensen
    For C++ development for 32-bit systems (be it Linux, Mac OS or Windows, PowerPC or x86) I have initialised pointers that would otherwise be undefined (e.g. they can not immediately get a proper value) like so: int *pInt = reinterpret_cast<int *>(0xDEADBEEF); (To save typing and being DRY the right-hand side would normally be in a constant, e.g. BAD_PTR.) If pInt is dereferenced before it gets a proper value then it will crash immediately on most systems (instead of crashing much later when some memory is overwritten or going into a very long loop). Of course the behavior is dependent on the underlying hardware (getting a 4 byte integer from the odd address 0xDEADBEEF from a user process may be perfectly valid), but the crashing has been 100% reliable for all the systems I have developed for so far (Mac OS 68xxx, Mac OS PowerPC, Linux Redhat Pentium, Windows GUI Pentium, Windows console Pentium). For instance on PowerPC it is illegal (bus fault) to fetch a 4 byte integer from an odd address. What is a good value for this on 64-bit systems?

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  • Coding for fun

    - by Klelky
    I would describe myself as a career coder - i.e. a developer at work but never really coded for fun. Early in my career I've hit the management track though. I really like my current job and can't see me going back to coding anytime soon so: Whats the best way to develop my coding skills and learn new languages in my spare time?

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  • Linker library for OpenMP for Snow Leopard?

    - by unknownthreat
    Currently, I am trying out OpenMP on XCode 3.2.2 on Snow Leopard: #include <omp.h> #include <iostream> #include <stdio.h> int main (int argc, char * const argv[]) { #pragma omp parallel printf("Hello from thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads()); return 0; } I didn't include any linking libraries yet, so the linker complains: "_omp_get_thread_num", referenced from: _main in main.o "_omp_get_num_threads", referenced from: _main in main.o OK, fine, no problem, I take a look in the existing framework, looking for keywords such as openmp or omp... here comes the problem, where is the linking library? Or should I say, what is the name of the linking library for openMP? Is it dylib, framework or what? Or do I need to get it from somewhere first?

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  • F#: how to find Cartesian power

    - by Nike
    I have a problem with writing a Cartesian power function. I found many examples about calculating Cartesian Product, but no one about Cartesian power. For example, [1;2] raised to power 3 = [ [1;1;1] ; [1;1;2] ; [1;2;1] ; [1;2;2] ; [2;1;1] ; [2;1;2] ; [2;2;1]; [2;2;2] ] I use following code to calculate Cartesian Product: let Cprod U V = let mutable res = [] for u in U do for v in V do res <- res @ [[u;v]] res And trying to calculate Cartesian power. I use following code to calculate Cartesian Product: let Cpower U n = let mutable V = U for i=0 to n-1 do V <- Dprod U V V Visual Studio said: Error The resulting type would be infinite when unifying ''a' and ''a list'. I will thankful for any help and links.

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  • A question for retrieve minix os version

    - by majnun
    Hi guys i'm having a project for the university in which (above others ) i have to get the minix os version from kernell call.I'm not a very experienced programmer so this is what i have come to (with some help ) int main (int argc, char *argv[] ) { char M3ca1[23]; message ml; m.m_u.m_m1.m3ca1= OS_VERSION; char temp=_syscall(MM,69,&m); printf("the os version is %c\n",temp); return 0; } and i get multiple errors.IF you have any ideas it would be greatly appreciated.

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  • How to simulate a dial-up connection for testing purposes?

    - by mawg
    I have to code a server app where clients open a TCP/IP socket, send some data and close the connection. The data packets are small < 100 bytes, however there is talk of having them batch their transactions and send multiple packets. How can I best simulate a dial-up ut connection (using Delphy & Indy components, just FYI)? Is it as simple as open connection wait a while (what is the definition of "a while"?) close connection

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  • Folder View in C# Form

    - by Kiran
    Hello, In an attempt to learn C#, I am trying to develop Picasa Like Application to display Photographs from my Library. Would it be possible to display folders as in Picasa Using C# ? Any help would be highly helpful.

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  • From interpeted to native code: "dynamic" languages compiler support

    - by Daniel
    First, I am aware that dynamic languages is a term used mainly by a vendor; I am using it just to have a container word to include languages like Perl (a favorite of mine), Python, Tcl, Ruby, PHP and so on. They are interpreted but I am interested here to refer to languages featuring strong capability to support the programmer efficiency and the support for typical constructs of modern interpreted languages My question is: there are dynamic languages can be compiled efficiently in native executable code - typically for Windows platforms? Which ones? Maybe using some third part ad-hoc tools? I am not talking about huge executables carrying with them a full interpreter or some similar tricks nor some smart module able to include its own dependances or some required modules, but a honest, straight, standard, solid executable code. If not, there is some technical reason inhibiting the availability of such a best-of-both-world feature? Thanks! Daniel

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  • Parallel processing via multithreading in Java

    - by Robz
    There are certain algorithms whose running time can decrease significantly when one divides up a task and gets each part done in parallel. One of these algorithms is merge sort, where a list is divided into infinitesimally smaller parts and then recombined in a sorted order. I decided to do an experiment to test whether or not I could I increase the speed of this sort by using multiple threads. I am running the following functions in Java on a Quad-Core Dell with Windows Vista. One function (the control case) is simply recursive: // x is an array of N elements in random order public int[] mergeSort(int[] x) { if (x.length == 1) return x; // Dividing the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Sending them off to continue being divided mergeSort(a); mergeSort(b); // Recombining the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } return x; } The other is in the 'run' function of a class that extends thread, and recursively creates two new threads each time it is called: public class Merger extends Thread { int[] x; boolean finished; public Merger(int[] x) { this.x = x; } public void run() { if (x.length == 1) { finished = true; return; } // Divide the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Begin two threads to continue to divide the array Merger ma = new Merger(a); ma.run(); Merger mb = new Merger(b); mb.run(); // Wait for the two other threads to finish while(!ma.finished || !mb.finished) ; // Recombine the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } finished = true; } } It turns out that function that does not use multithreading actually runs faster. Why? Does the operating system and the java virtual machine not "communicate" effectively enough to place the different threads on different cores? Or am I missing something obvious?

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  • C# Asynchronous Network IO and OutOfMemoryException

    - by The.Anti.9
    I'm working on a client/server application in C#, and I need to get Asynchronous sockets working so I can handle multiple connections at once. Technically it works the way it is now, but I get an OutOfMemoryException after about 3 minutes of running. MSDN says to use a WaitHandler to do WaitOne() after the socket.BeginAccept(), but it doesn't actually let me do that. When I try to do that in the code it says WaitHandler is an abstract class or interface, and I can't instantiate it. I thought maybe Id try a static reference, but it doesnt have teh WaitOne() method, just WaitAll() and WaitAny(). The main problem is that in the docs it doesn't give a full code snippet, so you can't actually see what their "wait handler" is coming from. its just a variable called allDone, which also has a Reset() method in the snippet, which a waithandler doesn't have. After digging around in their docs, I found some related thing about an AutoResetEvent in the Threading namespace. It has a WaitOne() and a Reset() method. So I tried that around the while(true) { ... socket.BeginAccept( ... ); ... }. Unfortunately this makes it only take one connection at a time. So I'm not really sure where to go. Here's my code: class ServerRunner { private Byte[] data = new Byte[2048]; private int size = 2048; private Socket server; static AutoResetEvent allDone = new AutoResetEvent(false); public ServerRunner() { server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); IPEndPoint iep = new IPEndPoint(IPAddress.Any, 33333); server.Bind(iep); Console.WriteLine("Server initialized.."); } public void Run() { server.Listen(100); Console.WriteLine("Listening..."); while (true) { //allDone.Reset(); server.BeginAccept(new AsyncCallback(AcceptCon), server); //allDone.WaitOne(); } } void AcceptCon(IAsyncResult iar) { Socket oldserver = (Socket)iar.AsyncState; Socket client = oldserver.EndAccept(iar); Console.WriteLine(client.RemoteEndPoint.ToString() + " connected"); byte[] message = Encoding.ASCII.GetBytes("Welcome"); client.BeginSend(message, 0, message.Length, SocketFlags.None, new AsyncCallback(SendData), client); } void SendData(IAsyncResult iar) { Socket client = (Socket)iar.AsyncState; int sent = client.EndSend(iar); client.BeginReceive(data, 0, size, SocketFlags.None, new AsyncCallback(ReceiveData), client); } void ReceiveData(IAsyncResult iar) { Socket client = (Socket)iar.AsyncState; int recv = client.EndReceive(iar); if (recv == 0) { client.Close(); server.BeginAccept(new AsyncCallback(AcceptCon), server); return; } string receivedData = Encoding.ASCII.GetString(data, 0, recv); //process received data here byte[] message2 = Encoding.ASCII.GetBytes("reply"); client.BeginSend(message2, 0, message2.Length, SocketFlags.None, new AsyncCallback(SendData), client); } }

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  • what is pagecache page

    - by kumar
    /* * Each physical page in the system has a struct page associated with * it to keep track of whatever it is we are using the page for at the * moment. Note that we have no way to track which tasks are using * a page, though if it is a pagecache page, rmap structures can tell us * who is mapping it. */ include/linux/mm_types.h Here Please lemme know what is "pagecache page" means? Thanks!

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  • How is a referencing environment generally implemented for closures?

    - by Alexandr Kurilin
    Let's say I have a statically/lexically scoped language with deep binding and I create a closure. The closure will consist of the statements I want executed plus the so called referencing environment, or, to quote this post, the collection of variables which can be used. What does this referencing environment actually look like implementation-wise? I was recently reading about ObjectiveC's implementation of blocks, and the author suggests that behind the scenes you get a copy of all of the variables on the stack and also of all the references to heap objects. The explanation claims that you get a "snapshot" of the referencing environment at the point in time of the closure's creation. Is that more or less what happens, or did I misread that? Is anything done to "freeze" a separate copy of the heap objects, or is it safe to assume that if they get modified between closure creation and the closure executing, the closure will no longer be operating on the original version of the object? If indeed there's copying being made, are there memory usage considerations in situations where one might want to create plenty of closures and store them somewhere? I think that misunderstanding of some of these concepts might lead to tricky issues like the ones Eric Lippert mentions in this blog post. It's interesting because you'd think that it wouldn't make sense to keep a reference to a value type that might be gone by the time the closure is called, but I'm guessing that in C# the compiler will figure out that the variable is needed later and put it into the heap instead. It seems that in most memory-managed languages everything is a reference and thus ObjectiveC is a somewhat unique situation with having to deal with copying what's on the stack.

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  • How to number the ls output in unix?

    - by Snehal
    I am trying to write a file with format - "id file_absolute_path" which basically lists down all the files recursively in a folder and give an identifier to each file listed like 1,2,3,4. I can get the absolute path of the files recursively using the following command: ls -d -1 $PWD/**/*/* However, I am unable to give an identifier from the output of the ls command. I am sure this can be done using awk, but can't seem to solve it.

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  • scripting in awk

    - by benjamin button
    I have a text file with contents as below: 1,A,100 2,A,200 3,B,150 4,B,100 5,B,250 i need the output as : A,300 B,500 the logic here is sum of all the 3rd fields whose 2nd field is A and in the same way for B how could we do it using awk?

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