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  • conditionally enabling constructor

    - by MK
    Here is how I can conditionally enable a constructor of a class : struct Foo { template<class T> Foo( T* ptr, boost::enable_if<is_arithmetic<T> >::type* = NULL ) {} }; I would like to know why I need to do the enabling via a dummy parameter. Why can I not just write : struct Foo { template<class T> Foo( boost::enable_if<is_arithmetic<T>, T>::type* = NULL ) {} };

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  • C++, what does this syntax mean?

    - by aaa
    i found this in this file: http://www.boost.org/doc/libs/1_43_0/boost/spirit/home/phoenix/core/actor.hpp What does this syntax means? struct actor ... { ... template <typename T0, typename T1> typename result<actor(T0&,T1&)>::type // this line thank you

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  • SignalR Auto Disconnect when Page Changed in AngularJS

    - by Shaun
    Originally posted on: http://geekswithblogs.net/shaunxu/archive/2014/05/30/signalr-auto-disconnect-when-page-changed-in-angularjs.aspxIf we are using SignalR, the connection lifecycle was handled by itself very well. For example when we connect to SignalR service from browser through SignalR JavaScript Client the connection will be established. And if we refresh the page, close the tab or browser, or navigate to another URL then the connection will be closed automatically. This information had been well documented here. In a browser, SignalR client code that maintains a SignalR connection runs in the JavaScript context of a web page. That's why the SignalR connection has to end when you navigate from one page to another, and that's why you have multiple connections with multiple connection IDs if you connect from multiple browser windows or tabs. When the user closes a browser window or tab, or navigates to a new page or refreshes the page, the SignalR connection immediately ends because SignalR client code handles that browser event for you and calls the "Stop" method. But unfortunately this behavior doesn't work if we are using SignalR with AngularJS. AngularJS is a single page application (SPA) framework created by Google. It hijacks browser's address change event, based on the route table user defined, launch proper view and controller. Hence in AngularJS we address was changed but the web page still there. All changes of the page content are triggered by Ajax. So there's no page unload and load events. This is the reason why SignalR cannot handle disconnect correctly when works with AngularJS. If we dig into the source code of SignalR JavaScript Client source code we will find something below. It monitors the browser page "unload" and "beforeunload" event and send the "stop" message to server to terminate connection. But in AngularJS page change events were hijacked, so SignalR will not receive them and will not stop the connection. 1: // wire the stop handler for when the user leaves the page 2: _pageWindow.bind("unload", function () { 3: connection.log("Window unloading, stopping the connection."); 4:  5: connection.stop(asyncAbort); 6: }); 7:  8: if (isFirefox11OrGreater) { 9: // Firefox does not fire cross-domain XHRs in the normal unload handler on tab close. 10: // #2400 11: _pageWindow.bind("beforeunload", function () { 12: // If connection.stop() runs runs in beforeunload and fails, it will also fail 13: // in unload unless connection.stop() runs after a timeout. 14: window.setTimeout(function () { 15: connection.stop(asyncAbort); 16: }, 0); 17: }); 18: }   Problem Reproduce In the codes below I created a very simple example to demonstrate this issue. Here is the SignalR server side code. 1: public class GreetingHub : Hub 2: { 3: public override Task OnConnected() 4: { 5: Debug.WriteLine(string.Format("Connected: {0}", Context.ConnectionId)); 6: return base.OnConnected(); 7: } 8:  9: public override Task OnDisconnected() 10: { 11: Debug.WriteLine(string.Format("Disconnected: {0}", Context.ConnectionId)); 12: return base.OnDisconnected(); 13: } 14:  15: public void Hello(string user) 16: { 17: Clients.All.hello(string.Format("Hello, {0}!", user)); 18: } 19: } Below is the configuration code which hosts SignalR hub in an ASP.NET WebAPI project with IIS Express. 1: public class Startup 2: { 3: public void Configuration(IAppBuilder app) 4: { 5: app.Map("/signalr", map => 6: { 7: map.UseCors(CorsOptions.AllowAll); 8: map.RunSignalR(new HubConfiguration() 9: { 10: EnableJavaScriptProxies = false 11: }); 12: }); 13: } 14: } Since we will host AngularJS application in Node.js in another process and port, the SignalR connection will be cross domain. So I need to enable CORS above. In client side I have a Node.js file to host AngularJS application as a web server. You can use any web server you like such as IIS, Apache, etc.. Below is the "index.html" page which contains a navigation bar so that I can change the page/state. As you can see I added jQuery, AngularJS, SignalR JavaScript Client Library as well as my AngularJS entry source file "app.js". 1: <html data-ng-app="demo"> 2: <head> 3: <script type="text/javascript" src="jquery-2.1.0.js"></script> 1:  2: <script type="text/javascript" src="angular.js"> 1: </script> 2: <script type="text/javascript" src="angular-ui-router.js"> 1: </script> 2: <script type="text/javascript" src="jquery.signalR-2.0.3.js"> 1: </script> 2: <script type="text/javascript" src="app.js"></script> 4: </head> 5: <body> 6: <h1>SignalR Auto Disconnect with AngularJS by Shaun</h1> 7: <div> 8: <a href="javascript:void(0)" data-ui-sref="view1">View 1</a> | 9: <a href="javascript:void(0)" data-ui-sref="view2">View 2</a> 10: </div> 11: <div data-ui-view></div> 12: </body> 13: </html> Below is the "app.js". My SignalR logic was in the "View1" page and it will connect to server once the controller was executed. User can specify a user name and send to server, all clients that located in this page will receive the server side greeting message through SignalR. 1: 'use strict'; 2:  3: var app = angular.module('demo', ['ui.router']); 4:  5: app.config(['$stateProvider', '$locationProvider', function ($stateProvider, $locationProvider) { 6: $stateProvider.state('view1', { 7: url: '/view1', 8: templateUrl: 'view1.html', 9: controller: 'View1Ctrl' }); 10:  11: $stateProvider.state('view2', { 12: url: '/view2', 13: templateUrl: 'view2.html', 14: controller: 'View2Ctrl' }); 15:  16: $locationProvider.html5Mode(true); 17: }]); 18:  19: app.value('$', $); 20: app.value('endpoint', 'http://localhost:60448'); 21: app.value('hub', 'GreetingHub'); 22:  23: app.controller('View1Ctrl', function ($scope, $, endpoint, hub) { 24: $scope.user = ''; 25: $scope.response = ''; 26:  27: $scope.greeting = function () { 28: proxy.invoke('Hello', $scope.user) 29: .done(function () {}) 30: .fail(function (error) { 31: console.log(error); 32: }); 33: }; 34:  35: var connection = $.hubConnection(endpoint); 36: var proxy = connection.createHubProxy(hub); 37: proxy.on('hello', function (response) { 38: $scope.$apply(function () { 39: $scope.response = response; 40: }); 41: }); 42: connection.start() 43: .done(function () { 44: console.log('signlar connection established'); 45: }) 46: .fail(function (error) { 47: console.log(error); 48: }); 49: }); 50:  51: app.controller('View2Ctrl', function ($scope, $) { 52: }); When we went to View1 the server side "OnConnect" method will be invoked as below. And in any page we send the message to server, all clients will got the response. If we close one of the client, the server side "OnDisconnect" method will be invoked which is correct. But is we click "View 2" link in the page "OnDisconnect" method will not be invoked even though the content and browser address had been changed. This might cause many SignalR connections remain between the client and server. Below is what happened after I clicked "View 1" and "View 2" links four times. As you can see there are 4 live connections.   Solution Since the reason of this issue is because, AngularJS hijacks the page event that SignalR need to stop the connection, we can handle AngularJS route or state change event and stop SignalR connect manually. In the code below I moved the "connection" variant to global scope, added a handler to "$stateChangeStart" and invoked "stop" method of "connection" if its state was not "disconnected". 1: var connection; 2: app.run(['$rootScope', function ($rootScope) { 3: $rootScope.$on('$stateChangeStart', function () { 4: if (connection && connection.state && connection.state !== 4 /* disconnected */) { 5: console.log('signlar connection abort'); 6: connection.stop(); 7: } 8: }); 9: }]); Now if we refresh the page and navigated to View 1, the connection will be opened. At this state if we clicked "View 2" link the content will be changed and the SignalR connection will be closed automatically.   Summary In this post I demonstrated an issue when we are using SignalR with AngularJS. The connection cannot be closed automatically when we navigate to other page/state in AngularJS. And the solution I mentioned below is to move the SignalR connection as a global variant and close it manually when AngularJS route/state changed. You can download the full sample code here. Moving the SignalR connection as a global variant might not be a best solution. It's just for easy to demo here. In production code I suggest wrapping all SignalR operations into an AngularJS factory. Since AngularJS factory is a singleton object, we can safely put the connection variant in the factory function scope.   Hope this helps, Shaun All documents and related graphics, codes are provided "AS IS" without warranty of any kind. Copyright © Shaun Ziyan Xu. This work is licensed under the Creative Commons License.

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  • Apple’s Sep 10th event confirmed. iPhone 5S and low cost iPhone 5C launch is expected

    - by Gopinath
    The much rumored Apple event on September 10th is confirmed. Apple sent official event invitations to media houses and popular bloggers across the globe with the title "This should brighten your day". For the past couple of months there are a lot of speculations on next generation iPhone. Media and bloggers are dubbing it as iPhone 5S and rumored to have finger print sensor for biometric authentication, 12- or 13-megapixel camera with dual-LED flash, and a gold-colored variant. Another speculated surprise Apple may pull out is a low cost variant of iPhone called as iPhone 5C. In order to fight Android penetration, Apple is speculated to announce a plastic iPhone in multiple bold colors similar to the Nokia phones. The new iPhones will be running on iOS 7, a new flat UI which is drastically different from previous versions. iOS 7 is in beta for several months and it heavily barrowed user interface clues from Microsoft’s Windows 8 operating system. What ever Apple is going to introduce on September 10th, gadget freaks and investors are eagerly waiting to see if Apple can continue innovating after Steve Jobs. Since 2011 this is the big launch

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  • Using virt-install to mount multiple cdrom drives/images

    - by Dana the Sane
    I would like to create a windows xp guest from the windows xp upgrade cd I have, along with one of a few full versions I have around. However, when I reach the stage in the installer where I am prompted to insert a full version cd, the installer can't find it, i.e.: Setup could not read the CD you inserted, or the CD is not a valid Windows CD.. Is there a work-around for this?, my Googling didn't uncover anything. I've tried various combinations of mounting .iso files and specifying disks, such as: $sudo virt-install --accelerate --connect qemu:///system -n xpsp1 -r 2048 --disk ./vm/winxp_sp1.iso,device=cdrom --disk ./vm/windows.qcow2,size=12 --vnc --noautoconsole --os-type windows --os-variant winxp --vcpus 2 -c /dev/cdrom --check-cpu If I try to specify multiple cdrom drives, I receive an error: virt-install --accelerate --connect qemu:///system -n xpsp1 -r 2048 --disk ./vm/winxp_sp1.iso,device=cdrom --disk /dev/cdrom,device=cdrom --disk ./vm/windows.qcow2,size=12 --vnc --noautoconsole --os-type windows --os-variant winxp --vcpus 2 --check-cpu Starting install... ERROR IDE CDROM must use 'hdc', but target in use.

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  • Diagnosing xmodmap errors

    - by intuited
    I'm getting this error when trying to use xmodmap to get rid of caps lock: $ xmodmap -e 'clear Lock' X Error of failed request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 118 (X_SetModifierMapping) Value in failed request: 0x17 Serial number of failed request: 8 Current serial number in output stream: 8 I'm running xfce on Maverick "10.10" Meercat. This problem did not occur before I added the Keyboard Layouts applet to a panel; before doing that, I was able to run my xmodmap script to swap Esc and CapsLock: !Remap Caps_Lock as Escape remove Lock = Caps_Lock keysym Caps_Lock = Escape It may be relevant that I chose alt-capslock as the keyboard switch combo in the Keyboard Layouts preferences. I've had a similar problem before, on a different machine, running openbox. On that machine, this problem started when I upgraded to Lucid, and has persisted in Maverick (release 10.10). I reported a bug in xorg. However, it remains unclear whether it's really a problem with xorg, or if I'm just doing something wrong with my configuration. Have other people experienced this problem? Can someone shed some light on what's going on here? It seems there are quite a few layers involved, and I don't understand any of them particularly well, so any information would be helpful. update I've discovered that the problem is specifically triggered by adding the Canada layout variant "Multilingual" (ca-multix). If I instead add the variant "Multilingual (first part)", the problem does not occur. I think this will probably end up being a usable workaround, but I don't yet know what the difference between these variants is. I've filed a freedesktop issue, and am commenting on a related ubuntu issue.

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  • Diagnosing xmodmap errors

    - by intuited
    I'm getting this error when trying to use xmodmap to get rid of caps lock: $ xmodmap -e 'clear Lock' X Error of failed request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 118 (X_SetModifierMapping) Value in failed request: 0x17 Serial number of failed request: 8 Current serial number in output stream: 8 I'm running xfce on Maverick "10.10" Meercat. This problem did not occur before I added the Keyboard Layouts applet to a panel; before doing that, I was able to run my xmodmap script to swap Esc and CapsLock: !Remap Caps_Lock as Escape remove Lock = Caps_Lock keysym Caps_Lock = Escape It may be relevant that I chose alt-capslock as the keyboard switch combo in the Keyboard Layouts preferences. I've had a similar problem before, on a different machine, running openbox. On that machine, this problem started when I upgraded to Lucid, and has persisted in Maverick (release 10.10). I reported a bug in xorg. However, it remains unclear whether it's really a problem with xorg, or if I'm just doing something wrong with my configuration. Have other people experienced this problem? Can someone shed some light on what's going on here? It seems there are quite a few layers involved, and I don't understand any of them particularly well, so any information would be helpful. update I've discovered that the problem is specifically triggered by adding the Canada layout variant "Multilingual" (ca-multix). If I instead add the variant "Multilingual (first part)", the problem does not occur. I think this will probably end up being a usable workaround, but I don't yet know what the difference between these variants is. I've filed a freedesktop issue, and am commenting on a related ubuntu issue.

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  • Authorization design-pattern / practice?

    - by Lawtonfogle
    On one end, you have users. On the other end, you have activities. I was wondering if there is a best practice to relate the two. The simplest way I can think of is to have every activity have a role, and assign every user every role they need. The problem is that this gets really messy in practice as soon as you go beyond a trivial system. A way I recently designed was to have users who have roles, and roles have privileges, and activities require some combinations of privileges. For the trivial case, this is more complex, but I think it will scale better. But after I implemented it, I felt like it was overkill for the system I had. Another option would be to have users, who have roles, and activities require you to have a certain role to perform with many activities sharing roles. A more complex variant of this would given activities many possible roles, which you only needed one of. And an even more complex variant would be to allow logical statements of role ownership to use an activity (i.e. Must have A and (B exclusive or C) and must not have D). I could continue to list more, but I think this already gives a picture. And many of these have trade offs. But in software design, there are oftentimes solutions, while perhaps not perfect in every possible case, are clearly top of the pack to an extent it isn't even considered opinion based (i.e. how to store passwords, plain text is worse, hashing better, hashing and salt even better, despite the increased complexity of each level) (i.e. 2, Smart UI designs for applications are bad, even if it is subjective as to what the best design is). So, is there a best practice for authorization design that is not purely opinion based/subjective?

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  • How to plan/manage multi-platform (mobile) products?

    - by PhD
    Say I've to develop an app that runs on iOS, Android and Windows 8 Mobile. Now all three platforms are technically in different program languages. The only 'reuse' that I can see is that of the boxes-and-lines drawings (UML :) charts and nothing else. So how do companies/programmers manage the variation of the same product across different platforms especially since the implementation languages differ? It's 'easier' in the desktop world IMO given the plethora of languages and cross-platform libraries to make your life easier. Not so in the mobile world. More so, product line management principles don't seem to be all that applicable - what is same and variant doesn't really matter - the application is the same (conceptually) and the implementation is variant. Some difficulties that come to mind: Bug Fixing: Applications maybe designed in a similar manner but the bug identification and fixing would be radically different. A bug on iOS may/may-not be existent for that on Android. Or a bug fix approach on one platform may not be the same on another (unless it's a semantic bug like a!=b instead of a==b which would require the same 'approach' to fixing in essence Enhancements: Making a change on one platform would be radically different than on another Code-Design Divergence: They way the code is written/organized, the class structures etc., could be very different given the different implementation environments - leading to further reuse of the (above) UML models. There are of course many others - just keeping the development in sync and making sure all applications are up to the same version with the same set of features etc. Seems the effort is 3x that of a single application. So how exactly does one manage this nightmarish situation? Some thoughts: Split application to client/server to minimize the effect to client side only (not always doable) Use frameworks like Unity-3D that could take care of the cross-platform problem (mostly applicable to games and probably not to other applications etc.) Any other ways of managing a platform line? What are some proven approaches to managing/taming the effects?

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  • How to fill in Different String Values in Different Cells in Excel 2007 VBA marcos

    - by user325160
    Hello everyone, So I am trying to fill in Values "A-Z, 0-9" in a 2007 excel macro in four different locations (I am trying to put A-Z and 0-9 in cells: a1 to d9, e1 to h9, a10 to d18, and e10 to h18). So far I have the code: Sub TwoDArrays() Dim Matrix(9, 4) As Variant Dim Matrix2(9, 4) As Variant Dim Matrix3(9, 4) As Variant Dim Matrix4(9, 4) As Variant Matrix(1, 1) = "A" Matrix(1, 2) = "B" Matrix(1, 3) = "C" Matrix(1, 4) = "D" Matrix(2, 1) = "E" Matrix(2, 2) = "F" Matrix(2, 3) = "G" Matrix(2, 4) = "H" Matrix(3, 1) = "I" Matrix(3, 2) = "J" Matrix(3, 3) = "K" Matrix(3, 4) = "L" Matrix(4, 1) = "M" Matrix(4, 2) = "N" Matrix(4, 3) = "O" Matrix(4, 4) = "P" Matrix(5, 1) = "Q" Matrix(5, 2) = "R" Matrix(5, 3) = "S" Matrix(5, 4) = "T" Matrix(6, 1) = "U" Matrix(6, 2) = "V" Matrix(6, 3) = "W" Matrix(6, 4) = "X" Matrix(7, 1) = "Y" Matrix(7, 2) = "Z" Matrix(7, 3) = "0" Matrix(7, 4) = "1" Matrix(8, 1) = "2" Matrix(8, 2) = "3" Matrix(8, 3) = "4" Matrix(8, 4) = "5" Matrix(9, 1) = "6" Matrix(9, 2) = "7" Matrix(9, 3) = "8" Matrix(9, 4) = "9" Matrix2(1, 1) = "A" Matrix2(1, 2) = "B" Matrix2(1, 3) = "C" Matrix2(1, 4) = "D" Matrix2(2, 1) = "E" Matrix2(2, 2) = "F" Matrix2(2, 3) = "G" Matrix2(2, 4) = "H" Matrix2(3, 1) = "I" Matrix2(3, 2) = "J" Matrix2(3, 3) = "K" Matrix2(3, 4) = "L" Matrix2(4, 1) = "M" Matrix2(4, 2) = "N" Matrix2(4, 3) = "O" Matrix2(4, 4) = "P" Matrix2(5, 1) = "Q" Matrix2(5, 2) = "R" Matrix2(5, 3) = "S" Matrix2(5, 4) = "T" Matrix2(6, 1) = "U" Matrix2(6, 2) = "V" Matrix2(6, 3) = "W" Matrix2(6, 4) = "X" Matrix2(7, 1) = "Y" Matrix2(7, 2) = "Z" Matrix2(7, 3) = "0" Matrix2(7, 4) = "1" Matrix2(8, 1) = "2" Matrix2(8, 2) = "3" Matrix2(8, 3) = "4" Matrix2(8, 4) = "5" Matrix2(9, 1) = "6" Matrix2(9, 2) = "7" Matrix2(9, 3) = "8" Matrix2(9, 4) = "9" Matrix3(1, 1) = "A" Matrix3(1, 2) = "B" Matrix3(1, 3) = "C" Matrix3(1, 4) = "D" Matrix3(2, 1) = "E" Matrix3(2, 2) = "F" Matrix3(2, 3) = "G" Matrix3(2, 4) = "H" Matrix3(3, 1) = "I" Matrix3(3, 2) = "J" Matrix3(3, 3) = "K" Matrix3(3, 4) = "L" Matrix3(4, 1) = "M" Matrix3(4, 2) = "N" Matrix3(4, 3) = "O" Matrix3(4, 4) = "P" Matrix3(5, 1) = "Q" Matrix3(5, 2) = "R" Matrix3(5, 3) = "S" Matrix3(5, 4) = "T" Matrix3(6, 1) = "U" Matrix3(6, 2) = "V" Matrix3(6, 3) = "W" Matrix3(6, 4) = "X" Matrix3(7, 1) = "Y" Matrix3(7, 2) = "Z" Matrix3(7, 3) = "0" Matrix3(7, 4) = "1" Matrix3(8, 1) = "2" Matrix3(8, 2) = "3" Matrix3(8, 3) = "4" Matrix3(8, 4) = "5" Matrix3(9, 1) = "6" Matrix3(9, 2) = "7" Matrix3(9, 3) = "8" Matrix3(9, 4) = "9" Matrix4(1, 1) = "A" Matrix4(1, 2) = "B" Matrix4(1, 3) = "C" Matrix4(1, 4) = "D" Matrix4(2, 1) = "E" Matrix4(2, 2) = "F" Matrix4(2, 3) = "G" Matrix4(2, 4) = "H" Matrix4(3, 1) = "I" Matrix4(3, 2) = "J" Matrix4(3, 3) = "K" Matrix4(3, 4) = "L" Matrix4(4, 1) = "M" Matrix4(4, 2) = "N" Matrix4(4, 3) = "O" Matrix4(4, 4) = "P" Matrix4(5, 1) = "Q" Matrix4(5, 2) = "R" Matrix4(5, 3) = "S" Matrix4(5, 4) = "T" Matrix4(6, 1) = "U" Matrix4(6, 2) = "V" Matrix4(6, 3) = "W" Matrix4(6, 4) = "X" Matrix4(7, 1) = "Y" Matrix4(7, 2) = "Z" Matrix4(7, 3) = "0" Matrix4(7, 4) = "1" Matrix4(8, 1) = "2" Matrix4(8, 2) = "3" Matrix4(8, 3) = "4" Matrix4(8, 4) = "5" Matrix4(9, 1) = "6" Matrix4(9, 2) = "7" Matrix4(9, 3) = "8" Matrix4(9, 4) = "9" For i = 1 To 9 For j = 1 To 4 Cells(i, j) = Matrix(i, j) Next j Next i 'For i = 1 To 9 'For j = 1 To 4 ' Range("a1:d1", "a1:a10").Value = Matrix(i, j) 'Application.WorksheetFunction.Transpose (Matrix) 'Next j 'Next i End Sub However, at the top for loop where it does not use the Range function with the cells, I can only do this for cells a1:d9 (a1 to d9) and if I use the second for loop with the range, get the value 9 appearing in every cell from a1 to d9. So is there a way to make it so that I can get the values A-Z and 0-9 in the other cells I specified above? Thank you.

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  • Use of for_each on map elements

    - by Antonio
    I have a map where I'd like to perform a call on every data type object member function. I yet know how to do this on any sequence but, is it possible to do it on an associative container? The closest answer I could find was this: Boost.Bind to access std::map elements in std::for_each. But I cannot use boost in my project so, is there an STL alternative that I'm missing to boost::bind? If not possible, I thought on creating a temporary sequence for pointers to the data objects and then, call for_each on it, something like this: class MyClass { public: void Method() const; } std::map<int, MyClass> Map; //... std::vector<MyClass*> Vector; std::transform(Map.begin(), Map.end(), std::back_inserter(Vector), std::mem_fun_ref(&std::map<int, MyClass>::value_type::second)); std::for_each(Vector.begin(), Vector.end(), std::mem_fun(&MyClass::Method)); It looks too obfuscated and I don't really like it. Any suggestions?

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  • Find max integer size that a floating point type can handle without loss of precision

    - by Checkers
    Double has range more than a 64-bit integer, but its precision is less dues to its representation (since double is 64-bit as well, it can't fit more actual values). So, when representing larger integers, you start to lose precision in the integer part. #include <boost/cstdint.hpp> #include <limits> template<typename T, typename TFloat> void maxint_to_double() { T i = std::numeric_limits<T>::max(); TFloat d = i; std::cout << std::fixed << i << std::endl << d << std::endl; } int main() { maxint_to_double<int, double>(); maxint_to_double<boost::intmax_t, double>(); maxint_to_double<int, float>(); return 0; } This prints: 2147483647 2147483647.000000 9223372036854775807 9223372036854775800.000000 2147483647 2147483648.000000 Note how max int can fit into a double without loss of precision and boost::intmax_t (64-bit in this case) cannot. float can't even hold an int. Now, the question: is there a way in C++ to check if the entire range of a given integer type can fit into a loating point type without loss of precision? Preferably, it would be a compile-time check that can be used in a static assertion, and would not involve enumerating the constants the compiler should know or can compute.

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  • What would be the safest way to store objects of classes derived from a common interface in a common

    - by Svenstaro
    I'd like to manage a bunch of objects of classes derived from a shared interface class in a common container. To illustrate the problem, let's say I'm building a game which will contain different actors. Let's call the interface IActor and derive Enemy and Civilian from it. Now, the idea is to have my game main loop be able to do this: // somewhere during init std::vector<IActor> ActorList; Enemy EvilGuy; Civilian CoolGuy; ActorList.push_back(EvilGuy); ActorList.push_back(CoolGuy); and // main loop while(!done) { BOOST_FOREACH(IActor CurrentActor, ActorList) { CurrentActor.Update(); CurrentActor.Draw(); } } ... or something along those lines. This example obviously won't work but that is pretty much the reason I'm asking here. I'd like to know: What would be the best, safest, highest-level way to manage those objects in a common heterogeneous container? I know about a variety of approaches (Boost::Any, void*, handler class with boost::shared_ptr, Boost.Pointer Container, dynamic_cast) but I can't decide which would be the way to go here. Also I'd like to emphasize that I want to stay away as far as possible from manual memory management or nested pointers. Help much appreciated :).

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  • What is the rationale to non allow overloading of C++ conversions operator with non-member functio

    - by Vicente Botet Escriba
    C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration operator boost::posix_time::ptime( const boost::chrono::time_point& from) { using namespace boost; typedef chrono::time_point time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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  • Lucene setboost doesn't work

    - by Keven
    Hi all, OUr team just upgrade lucene from 2.3 to 3.0 and we are confused about the setboost and getboost of document. What we want is just set a boost for each document when add them into index, then when search it the documents in the response should have different order according to the boost I set. But it seems the order is not changed at all, even the boost of each document in the search response is still 1.0. Could some one give me some hit? Following is our code: String[] a = new String[] { "schindler", "spielberg", "shawshank", "solace", "sorcerer", "stone", "soap", "salesman", "save" }; List strings = Arrays.asList(a); AutoCompleteIndex index = new Index(); IndexWriter writer = new IndexWriter(index.getDirectory(), AnalyzerFactory.createAnalyzer("en_US"), true, MaxFieldLength.LIMITED); float i = 1f; for (String string : strings) { Document doc = new Document(); Field f = new Field(AutoCompleteIndexFactory.QUERYTEXTFIELD, string, Field.Store.YES, Field.Index.NOT_ANALYZED); doc.setBoost(i); doc.add(f); writer.addDocument(doc); i += 2f; } writer.close(); IndexReader reader2 = IndexReader.open(index.getDirectory()); for (int j = 0; j < reader2.maxDoc(); j++) { if (reader2.isDeleted(j)) { continue; } Document doc = reader2.document(j); Field f = doc.getField(AutoCompleteIndexFactory.QUERYTEXTFIELD); System.out.println(f.stringValue() + ":" + f.getBoost() + ", docBoost:" + doc.getBoost()); doc.setBoost(j); }

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  • noncopyable static const member class in template class

    - by Dukales
    I have a non-copyable (inherited from boost::noncopyable) class that I use as a custom namespace. Also, I have another class, that uses previous one, as shown here: #include <boost/utility.hpp> #include <cmath> template< typename F > struct custom_namespace : boost::noncopyable { F sqrt_of_half(F const & x) const { using std::sqrt; return sqrt(x / F(2.0L)); } // ... maybe others are not so dummy const/constexpr methods }; template< typename F > class custom_namespace_user { static ::custom_namespace< F > const custom_namespace_; public : F poisson() const { return custom_namespace_.sqrt_of_half(M_PI); } static F square_diagonal(F const & a) { return a * custom_namespace_.sqrt_of_half(1.0L); } }; template< typename F > ::custom_namespace< F > const custom_namespace_user< F >::custom_namespace_(); this code leads to the next error (even without instantiation): error: no 'const custom_namespace custom_namespace_user::custom_namespace_()' member function declared in class 'custom_namespace_user' The next way is not legitimate: template< typename F ::custom_namespace< F const custom_namespace_user< F ::custom_namespace_ = ::custom_namespace< F (); What should I do to declare this two classes (first as noncopyable static const member class of second)? Is this feaseble?

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  • What is the difference between Inversion of Control and Dependency injection in C++?

    - by rlbond
    I've been reading recently about DI and IoC in C++. I am a little confused (even after reading related questions here on SO) and was hoping for some clarification. It seems to me that being familiar with the STL and Boost leads to use of dependency injection quite a bit. For example, let's say I made a function that found the mean of a range of numbers: template <typename Iter> double mean(Iter first, Iter last) { double sum = 0; size_t number = 0; while (first != last) { sum += *(first++); ++number; } return sum/number; }; Is this dependency injection? Inversion of control? Neither? Let's look at another example. We have a class: class Dice { public: typedef boost::mt19937 Engine; Dice(int num_dice, Engine& rng) : n_(num_dice), eng_(rng) {} int roll() { int sum = 0; for (int i = 0; i < num_dice; ++i) sum += boost::uniform_int<>(1,6)(eng_); return sum; } private: Engine& eng_; int n_; }; This seems like dependency injection. But is it inversion of control? Also, if I'm missing something, can someone help me out?

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  • Why do you need "extern C" for in C++ callbacks to C functions?

    - by Artyom
    Hello, I find such examples in Boost code. namespace boost { namespace { extern "C" void *thread_proxy(void *f) { .... } } // anonymous void thread::thread_start(...) { ... pthread_create(something,0,&thread_proxy,something_else); ... } } // boost Why do you actually need this extern "C"? It is clear that thread_proxy function is private internal and I do not expect that it would be mangled as "thread_proxy" because I actually do not need it mangled at all. In fact in all my code that I had written and that runs on may platforms I never used extern "C" and this had worked as-as with normal functions. Why extern "C" is added? My problem is that extern "C" function pollute global name-space and they do not actually hidden as author expects. This is not duplicate! I'm not talking about mangling and external linkage. It is obvious in this code that external linkage is unwanted!

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  • How do I enforce the order of qmake library dependencies?

    - by James Oltmans
    I'm getting a lot of errors because qmake is improperly ordering the boost libraries I'm using. Here's what .pro file looks like QT += core gui TARGET = MyTarget TEMPLATE = app CONFIG += no_keywords \ link_pkgconfig SOURCES += file1.cpp \ file2.cpp \ file3.cpp PKGCONFIG += my_package \ sqlite3 LIBS += -lsqlite3 \ -lboost_signals \ -lboost_date_time HEADERS += file1.h\ file2.h\ file3.h FORMS += mainwindow.ui RESOURCES += Resources/resources.qrc This produces the following command: g++ -Wl,-O1 -o MyTarget file1.o file2.o file3.o moc_mainwindow.o -L/usr/lib/x86_64-linux-gnu -lboost_signals -lboost_date_time -L/usr/local/lib -lmylib1 -lmylib2 -lsqlite3 -lQtGui -lQtCore Note: mylib1 and mylib2 are statically compiled by another project, placed in /usr/local/lib with an appropriate pkg-config .pc file pointing there. The .pro file references them via my_package in PKGCONFIG. The problem is not with pkg-config's output but with Qt's ordering. Here's the .pc file: prefix=/usr/local exec_prefix=${prefix} libdir=${exec_prefix}/lib includedir=${prefix}/include Name: my_package Description: My component package Version: 0.1 URL: http://example.com Libs: -L${libdir} -lmylib1 -lmylib2 Cflags: -I${includedir}/my_package/ The linking stage fails spectacularly as mylib1 and mylib2 come up with a lot of undefined references to boost libraries that both the app and mylib1 and mylib2 are using. We have another build method using scons and it properly orders things for the linker. It's build command order is below. g++ -o MyTarget file1.o file2.o file3.o moc_mainwindow.o -L/usr/local/lib -lmylib1 -lmylib2 -lsqlite3 -lboost_signals -lboost_date_time -lQtGui -lQtCore Note that the principle difference is the order of the boost libs. Scons puts them at the end just before QtGui and QtCore while qmake puts them first. The other differences in the compile commands are unimportant as I have hand modified the qmake produced make file and the simple reordering fixed the problem. So my question is, how do I enforce the right order in my .pro file despite what qmake thinks they should be?

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  • Why do you need "extern C" for C++ callbacks to C functions?

    - by Artyom
    Hello, I find such examples in Boost code. namespace boost { namespace { extern "C" void *thread_proxy(void *f) { .... } } // anonymous void thread::thread_start(...) { ... pthread_create(something,0,&thread_proxy,something_else); ... } } // boost Why do you actually need this extern "C"? It is clear that thread_proxy function is private internal and I do not expect that it would be mangled as "thread_proxy" because I actually do not need it mangled at all. In fact in all my code that I had written and that runs on may platforms I never used extern "C" and this had worked as-as with normal functions. Why extern "C" is added? My problem is that extern "C" function pollute global name-space and they do not actually hidden as author expects. This is not duplicate! I'm not talking about mangling and external linkage. It is obvious in this code that external linkage is unwanted! Answer: Calling convention of C and C++ functions are not necessary the same, so you need to create one with C calling convention. See 7.5 (p4) of C++ standard.

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  • How to negate a predicate function using operator ! in C++?

    - by Chan
    Hi, I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well. struct my_is_digit { bool operator()( char c ) const { return c >= '0' && c <= '9'; } }; int main() { string s( "1a2b3c4d" ); s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() ); s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() ); cout << s << endl; return 0; } Then I tried my own version, the compiler complained :( error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea? Thanks, Chan Nguyen

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  • Including typedef of child in parent class

    - by Baz
    I have a class which looks something like this. I'd prefer to have the typedef of ParentMember in the Parent class and rename it Member. How might this be possible? The only way I can see is to have std::vector as a public member instead of using inheritance. typedef std::pair<std::string, boost::any> ParentMember; class Parent: public std::vector<ParentMember> { public: template <typename T> std::vector<T>& getMember(std::string& s) { MemberFinder finder(s); std::vector<ParentMember>::iterator member = std::find_if(begin(), end(), finder); boost::any& container = member->second; return boost::any_cast<std::vector<T>&>(container); } private: class Finder { ... }; };

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