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  • initializer_list and move semantics

    - by FredOverflow
    Am I allowed to move elements out of a std::initializer_list<T>? #include <initializer_list> #include <utility> template<typename T> void foo(std::initializer_list<T> list) { for (auto it = list.begin(); it != list.end(); ++it) { bar(std::move(*it)); // kosher? } } Since std::intializer_list<T> requires special compiler attention and does not have value semantics like normal containers of the C++ standard library, I'd rather be safe than sorry and ask.

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  • How to have a policy class implement a virtual function?

    - by dehmann
    I'm trying to design a policy-based class, where a certain interface is implemented by the policy itself, so the class derives from the policy, which itself is a template (I got this kind of thinking from Alexandrescu's book): #include <iostream> #include <vector> class TestInterface { public: virtual void test() = 0; }; class TestImpl1 { public: void test() {std::cerr << "Impl1" << std::endl;} }; template<class TestPolicy> class Foo : public TestInterface, TestPolicy { }; Then, in the main() function, I call test() on (potentially) various different objects that all implement the same interface: int main() { std::vector<TestInterface*> foos; foos.push_back(new Foo<TestImpl1>()); foos[0]->test(); delete foos[0]; return 0; } It doesn't compile, though, because the following virtual functions are pure within ‘Foo<TestImpl1>’: virtual void TestInterface::test() I thought TestInterface::test() is implemented because we derive from TestImpl1?

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  • Call the cast operator of template base class within the derived class

    - by yoni
    I have a template class, called Cell, here the definition: template <class T> class OneCell { ..... } I have a cast operator from Cell to T, here virtual operator const T() const { ..... } Now i have derived class, called DCell, here template <class T> class DCell : public Cell<T> { ..... } I need to override the Cell's cast operator (insert a little if), but after I need to call the Cell's cast operator. In other methods it's should be something like virtual operator const T() const { if (...) { return Cell<T>::operator const T; } else throw ... } but i got a compiler error error: argument of type 'const int (Cell::)()const' does not match 'const int' What can I do? Thank you, and sorry about my poor English.

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  • Architecture for Qt SIGNAL with subclass-specific, templated argument type

    - by Barry Wark
    I am developing a scientific data acquisition application using Qt. Since I'm not a deep expert in Qt, I'd like some architecture advise from the community on the following problem: The application supports several hardware acquisition interfaces but I would like to provide an common API on top of those interfaces. Each interface has a sample data type and a units for its data. So I'm representing a vector of samples from each device as a std::vector of Boost.Units quantities (i.e. std::vector<boost::units::quantity<unit,sample_type> >). I'd like to use a multi-cast style architecture, where each data source broadcasts newly received data to 1 or more interested parties. Qt's Signal/Slot mechanism is an obvious fit for this style. So, I'd like each data source to emit a signal like typedef std::vector<boost::units::quantity<unit,sample_type> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); for the unit and sample_type appropriate for that device. Since tempalted QObject subclasses aren't supported by the meta-object compiler, there doesn't seem to be a way to have a (tempalted) base class for all data sources which defines the samplesAcquired Signal. In other words, the following won't work: template<T,U> //sample type and units class DataSource : public QObject { Q_OBJECT ... public: typedef std::vector<boost::units::quantity<U,T> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); }; The best option I've been able to come up with is a two-layered approach: template<T,U> //sample type and units class IAcquiredSamples { public: typedef std::vector<boost::units::quantity<U,T> > SampleVector virtual shared_ptr<SampleVector> acquiredData(TimeStamp ts, unsigned long nsamples); }; class DataSource : public QObject { ... signals: void samplesAcquired(TimeStamp ts, unsigned long nsamples); }; The samplesAcquired signal now gives a timestamp and number of samples for the acquisition and clients must use the IAcquiredSamples API to retrieve those samples. Obviously data sources must subclass both DataSource and IAcquiredSamples. The disadvantage of this approach appears to be a loss of simplicity in the API... it would be much nicer if clients could get the acquired samples in the Slot connected. Being able to use Qt's queued connections would also make threading issues easier instead of having to manage them in the acquiredData method within each subclass. One other possibility, is to use a QVariant argument. This necessarily puts the onus on subclass to register their particular sample vector type with Q_REGISTER_METATYPE/qRegisterMetaType. Not really a big deal. Clients of the base class however, will have no way of knowing what type the QVariant value type is, unless a tag struct is also passed with the signal. I consider this solution at least as convoluted as the one above, as it forces clients of the abstract base class API to deal with some of the gnarlier aspects of type system. So, is there a way to achieve the templated signal parameter? Is there a better architecture than the one I've proposed?

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  • Register/Include javascript within RenderingTemplate.

    - by Janis Veinbergs
    Is it possible to register (include) javascript within RenderingTemplate? (RenderingTemplates are used to render list forms or fields) By using <SharePoint:RenderingTemplate ID="NewRelatedListItem" runat="server"> <Template> <span id="part1"> <SharePoint:ScriptLink Name="SPFormFieldAssistant.js" Localizable="false" /> ... </span> ... </Template> </SharePoint:RenderingTemplate> it couldn't be done - it didn't include script at HEAD area, but...: Is something wrong with my code? Althought script IS at Layouts folder and I checked with Reflector that it uses Layouts folder if Localizable='False'. I don't want this script to be loaded with every page, but only for forms. Any ideas on how this could be achieved?

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  • syntax help required on templated static member function

    - by omatai
    I have a bunch of containers of object pointers that I want to iterate through in different contexts to produce diagnostics for them. I'm struggling with the syntax required to define the functions... which, on account of these objects filtering through diverse parts of my application, seem best encapsulated in a dedicated diagnostics class thus: // Code sketch only - detail fleshed out below... class ObjectListDiagnoser { public: static void GenerateDiagnostics( /* help required here! */ ); }; ... // Elsewhere in the system... ObjectListDiagnoser::GenerateDiagnostics( /* help required here! */ ); What I'd like to be able to do (in places across my application) is at least this: std::vector<MyObject *> objGroup1; std::list<MyObject *> objGroup2; ObjectListDiagnoser::GenerateDiagnostics( objGroup1.begin(), objGroup1.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup2.begin(), objGroup2.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup1.rbegin(), objGroup1.rend() ); I have tried to template my function in two ways, with no success: class ObjectListDiagnoser { public: // 1 - nope. template <class ObjIter> static void GenerateDiagnostics( ObjIter first, ObjIter last ); // 2. - nope. template <class Container, class ObjIter> static void GenerateDiagnostics( Container<MyObject *>::ObjIter first, Container<MyObject *>::ObjIter last ); }; Can someone provide the correct syntax for this? The container type will vary, and the direction of iteration will vary, but always for the same type of object.

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  • Ambiguous access to base class template member function

    - by Johann Gerell
    In Visual Studio 2008, the compiler cannot resolve the call to SetCustomer in _tmain below and make it unambiguous: template <typename TConsumer> struct Producer { void SetConsumer(TConsumer* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; struct AppleConsumer { }; struct MeatConsumer { }; struct ShillyShallyProducer : public Producer<AppleConsumer>, public Producer<MeatConsumer> { }; int _tmain(int argc, _TCHAR* argv[]) { ShillyShallyProducer producer; AppleConsumer consumer; producer.SetConsumer(&consumer); // <--- Ambiguous call!! return 0; } This is the compilation error: // error C2385: ambiguous access of 'SetConsumer' // could be the 'SetConsumer' in base 'Producer<AppleConsumer>' // or could be the 'SetConsumer' in base 'Producer<MeatConsumer>' I thought the template argument lookup mechanism would be smart enough to deduce the correct base Producer. Why isn't it? I could get around this by changing Producer to template <typename TConsumer> struct Producer { template <typename TConsumer2> void SetConsumer(TConsumer2* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; and call SetConsumer as producer.SetConsumer<AppleConsumer>(&consumer); // Unambiguous call!! but it would be nicer if I didn't have to...

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  • error: expected constructor, destructor, or type conversion before '(' token

    - by jonathanasdf
    include/TestBullet.h:12: error: expected constructor, destructor, or type conver sion before '(' token I hate C++ error messages... lol ^^ Basically, I'm following what was written in this post to try to create a factory class for bullets so they can be instantiated from a string, which will be parsed from an xml file, because I don't want to have a function with a switch for all of the classes because that looks ugly. Here is my TestBullet.h: #pragma once #include "Bullet.h" #include "BulletFactory.h" class TestBullet : public Bullet { public: void init(BulletData& bulletData); void update(); }; REGISTER_BULLET(TestBullet); <-- line 12 And my BulletFactory.h: #pragma once #include <string> #include <map> #include "Bullet.h" #define REGISTER_BULLET(NAME) BulletFactory::reg<NAME>(#NAME) #define REGISTER_BULLET_ALT(NAME, CLASS) BulletFactory::reg<CLASS>(NAME) template<typename T> Bullet * create() { return new T; } struct BulletFactory { typedef std::map<std::string, Bullet*(*)()> bulletMapType; static bulletMapType map; static Bullet * createInstance(char* s) { std::string str(s); bulletMapType::iterator it = map.find(str); if(it == map.end()) return 0; return it->second(); } template<typename T> static void reg(std::string& s) { map.insert(std::make_pair(s, &create<T>)); } }; Thanks in advance.

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  • Can you declare <canvas> methods within a template in javascript?

    - by Binarytales
    Not entirely sure I posed the question in the best way but here goes... I have been playing around with the HTML5 canvas API and have got as far as drawing a shape in the canvas and getting it to move around with the arrow keys. I then tried to move my various variables and functions to a template so I could spawn multiple shapes (that would eventually be controlled by different keys). This is what I have: function player(x, y, z, colour, speed){ this.lx = x; this.ly = y; this.speed = 10; this.playerSize = z; this.colour = colour; } playerOne = new player(100, 100, 10, "#F0F"); function persona(z, colour){ zone.fillStyle = colour; offset = 0 - (z / 2); zone.fillRect(offset, offset, z, z); } function move(x, y){ playerOne.lx = playerOne.lx + x; playerOne.ly = playerOne.ly + y; zone.clearRect(0, 0, 500, 500); zone.save(); zone.translate(playerOne.lx, playerOne.ly); persona(playerOne.playerSize, playerOne.colour); zone.restore(); } window.onkeydown = function() { var direction = this.event.keyCode; var s = playerOne.speed; // Arrow Keys if( direction == 38 && playerOne.ly >= 10){ // Up move(0,-s); } if( direction == 40 && playerOne.ly <= 490){ // Down move(0,s); } if( direction == 37 && playerOne.lx >= 10){ // Left move(-s,0); } if( direction == 39 && playerOne.lx <= 490){ // Right move(s,0); } }; window.onload = function() { zone = document.getElementById('canvas').getContext('2d'); zone.save(); zone.translate(playerOne.lx, playerOne.ly); persona(playerOne.playerSize, playerOne.colour); zone.restore(); }; So what I tried to do was move the persona function into the player template like this: function player(x, y, z, colour, speed){ this.lx = x; this.ly = y; this.speed = 10; function persona(){ zone.fillStyle = colour; var offset = 0 - (z / 2); zone.fillRect(offset, offset, z, z); } } And then where before it said persona(playerOne.playerSize, playerOne.colour); it now just says playerOne.persona(); But this is just totally flaking out and not working and I can't figure out why. I'm probably going about it all the wrong way and I think the problem is that I'm trying to manipulate the canvas.context (call zone in my script) from within a object/template. Perhaps its nothing to do with that at all and I an just not declaring my persona functions properly in the context of the template. Documentation for the canvas API is very thin on the ground and any hint in the right direction will be very much appreciated.

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  • Default template parameters with forward declaration

    - by Seth Johnson
    Is it possible to forward declare a class that uses default arguments without specifying or knowing those arguments? For example, I would like to declare a boost::ptr_list< TYPE > in a Traits class without dragging the entire Boost library into every file that includes the traits. I would like to declare namespace boost { template<class T> class ptr_list< T >; }, but that doesn't work because it doesn't exactly match the true class declaration: template < class T, class CloneAllocator = heap_clone_allocator, class Allocator = std::allocator<void*> > class ptr_list { ... }; Are my options only to live with it or to specify boost::ptr_list< TYPE, boost::heap_clone_allocator, std::allocator<void*> in my traits class? (If I use the latter, I'll also have to forward declare boost::heap_clone_allocator and include <memory>, I suppose.) I've looked through Stroustrup's book, SO, and the rest of the internet and haven't found a solution. Usually people are concerned about not including STL, and the solution is "just include the STL headers." However, Boost is a much more massive and compiler-intensive library, so I'd prefer to leave it out unless I absolutely have to.

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  • Design pattern question: encapsulation or inheritance

    - by Matt
    Hey all, I have a question I have been toiling over for quite a while. I am building a templating engine with two main classes Template.php and Tag.php, with a bunch of extension classes like Img.php and String.php. The program works like this: A Template object creates a Tag objects. Each tag object determines which extension class (img, string, etc.) to implement. The point of the Tag class is to provide helper functions for each extension class such as wrap('div'), addClass('slideshow'), etc. Each Img or String class is used to render code specific to what is required, so $Img->render() would give something like <img src='blah.jpg' /> My Question is: Should I encapsulate all extension functionality within the Tag object like so: Tag.php function __construct($namespace, $args) { // Sort out namespace to determine which extension to call $this->extension = new $namespace($this); // Pass in Tag object so it can be used within extension return $this; // Tag object } function render() { return $this->extension->render(); } Img.php function __construct(Tag $T) { $args = $T->getArgs(); $T->addClass('img'); } function render() { return '<img src="blah.jpg" />'; } Usage: $T = new Tag("img", array(...); $T->render(); .... or should I create more of an inheritance structure because "Img is a Tag" Tag.php public static create($namespace, $args) { // Sort out namespace to determine which extension to call return new $namespace($args); } Img.php class Img extends Tag { function __construct($args) { // Determine namespace then call create tag $T = parent::__construct($namespace, $args); } function render() { return '<img src="blah.jpg" />'; } } Usage: $Img = Tag::create('img', array(...)); $Img->render(); One thing I do need is a common interface for creating custom tags, ie I can instantiate Img(...) then instantiate String(...), I do need to instantiate each extension using Tag. I know this is somewhat vague of a question, I'm hoping some of you have dealt with this in the past and can foresee certain issues with choosing each design pattern. If you have any other suggestions I would love to hear them. Thanks! Matt Mueller

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  • XSLT: Is there a way to "inherit" canned functionality?

    - by Ian Boyd
    i am once again having to cobble together a bit of XSLT into order to turn generated XML into (rather than simply generating HTML). i'm having huge deja-vu this time again. i'm once again having to solve again basic problems, e.g.: how to convert characters into valid html entity references how to preserve whitespace/carriage returns when converting to html how to convert to HTML as opposed to xhtml how to convert dates from xml format into presentable format how to tear apart strings with substring This is all stuff that i've solved many times before. But every time i come back to XSLT i have to start from scratch, re-inventing the wheel every time. If it were a programming language i would have a library of canned functions and procedures i can call. i would have subroutines to perform the commonly repeated tasks. i would inherit from a base class that already implements the ugly boilerplate stuff. Is there any way in XSLT to grow, expand and improve the ecosystem with canned code?

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  • Perl cgi @INC different in shell and in http request

    - by pistacchio
    Hi to all, I have the follwing, simplest per cgi script: use strict; use warnings; use CGI(); use CGI::Carp qw(fatalsToBrowser); use Template; print CGI::header(); foreach(@INC) { print "$_\n"; } When called (http://[..]/cgi-bin/p.cgi) I am given the following error: Can't locate Template.pm in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 .) at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. BEGIN failed--compilation aborted at /home/pistacchio/webapps/htdocs/cgi-bin/p.cgi line 8. I made sure that Template is installed and indeed when running this program from shell it works (loads Template) and outputs: Content-Type: text/html; charset=ISO-8859-1 /home/pistacchio/lib/perl5 /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /home/pistacchio/lib/perl5/lib /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 Template is installed in /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ pwd /home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [pistacchio@web118 i386-linux-thread-multi]$ ls auto perllocal.pod Template Template.pm This directory is correctly listed in env and, as previously posted, in @INC. In @INC it is shown twice, so I even tried to pop it out before calling use Template, but without result. From env: [pistacchio@web118 i386-linux-thread-multi]$ env [..] PERL5LIB=/home/pistacchio/lib/perl5:/home/pistacchio/lib/perl5/lib:/home/pistacchio/lib/perl5/lib/i386-linux-thread-multi [..] Removing use Template gets rid of the problem. Can anybody help?

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  • Convert templated parameter type to string

    - by wheaties
    I've got a small bit of DRY going on in code I and others have written that I'd like to reduce but I'm failing to figure out how to get it done. This is legacy COM code but it's interfering with the readability. I'd like to do the following: bool queryInterface<class T, class V>(T &_input, V &_output, Logger &_logger){ if( FAILED( _input->QueryInterface( &_output ) ) ){ _logger.error() << "Failed to Query Interface between " << MAGICHAPPENS<T>() << " and " << MAGICHAPPENS<V>(); return false; } if( _output == NULL ){ _logger.warn() << "Unable to Query Interface between " << MAGICHAPPENS<T>() << " and " << MAGICHAPPENS<V>(); return false; } } Wherein the "MAGICHAPPENS()" function would spit out the name of the variable type. Such that if "V" were a IQueryFilter I'd get back a string of "IQueryFilter." I can't think of any reasonable solution without having to write a bunch of template specializations totally defeating the point in the first place. Is there a way to write ANDMAGICHAPPENS?

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  • Minimalist, Tiny Javascript Template System?

    - by Parand
    I'm looking for a minimalist template system for javascript, ala John Resig's Javascript Micro Templating. The smaller the better, and if it's jquery based even better. Recommendations? I tried John's micro-templating but ran into a few issues, wanted to see if there are more baked / better packaged solutions out there. [Update] I tried Resig's Micro Templating again and it's working well for me. Would still like to hear about other alternatives if there are any.

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  • explicit template instantiations

    - by user323422
    see following code and please clear doubts1. as ABC is template why it not showing error when we put defination of ABC class member function in test.cpp 2.if i put test.cpp code in test.h and remve 2 , then it working fine. // test.h template <typename T> class ABC { public: void foo( T& ); void bar( T& ); }; // test.cpp template <typename T> void ABC<T>::foo( T& ) {} // definition template <typename T> void ABC<T>::bar( T& ) {} // definition template void ABC<char>::foo( char & ); // 1 template class ABC<char>; // 2 // main.cpp #include "test.h" int main() { ABC<char> a; a.foo(); // valid with 1 or 2 a.bar(); // link error if only 1, valid with 2 }

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  • Template problems: No matching function for call

    - by Nick Sweet
    I'm trying to create a template class, and when I define a non-member template function, I get the "No matching function for call to randvec()" error. I have a template class defined as: template <class T> class Vector { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y, const T& z); Vector(const Vector& u); //accessors T getx() const; T gety() const; T getz() const; //mutators void setx(const T& x); void sety(const T& y); void setz(const T& z); //operations void operator-(); Vector plus(const Vector& v); Vector minus(const Vector& v); Vector cross(const Vector& v); T dot(const Vector& v); void times(const T& s); T length() const; //Vector<T>& randvec(); //operators Vector& operator=(const Vector& rhs); friend std::ostream& operator<< <T>(std::ostream&, const Vector<T>&); }; and the function in question, which I've defined after all those functions above, is: //random Vector template <class T> Vector<double>& randvec() { const int min=-10, max=10; Vector<double>* r = new Vector<double>; int randx, randy, randz, temp; const int bucket_size = RAND_MAX/(max-min +1); temp = rand(); //voodoo hackery do randx = (rand()/bucket_size)+min; while (randx < min || randx > max); r->setx(randx); do randy = (rand()/bucket_size)+min; while (randy < min || randy > max); r->sety(randy); do randz = (rand()/bucket_size)+min; while (randz < min || randz > max); r->setz(randz); return *r; } Yet, every time I call it in my main function using a line like: Vector<double> a(randvec()); I get that error. However, if I remove the template and define it using 'double' instead of 'T', the call to randvec() works perfectly. Why doesn't it recognize randvec()? P.S. Don't mind the bit labeled voodoo hackery - this is just a cheap hack so that I can get around another problem I encountered.

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  • Comparison of web template engines

    - by Mark
    Post a snippet of code from your favorite templating engine, with the name of the engine and a link to its homepage; show off its basic syntax and maybe some neat features about it that makes it unique. Hopefully this will give people an idea of what's out there and make it easier for them to decide on an engine.

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  • Choosing the right template engine

    - by asrijaal
    Hi there, since today - I always used simple JSP Tags and JSTL which works but now I'm looking for a little bit more features and maybe more usability. With googling I've found Freemaker, Velocity and Tiles which seem to be very famous. Does someone of you has some further experiences with some of these and can give me a short brief about it. Or are there other frameworks which are worth to look into?

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  • Form resubmission issue-Django html

    - by Hulk
    There is a form ,which is submitted and then the page is redirected to another page.But if the user hits the refresh button again on the new page .the following message is displayed To display this page, Firefox must send information that will repeat any action (such as a search or order confirmation) that was performed earlier. And on press "OK" A duplicate entry is created how do i prevent this or how do i handle this I am using a django,application Thanks..

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  • PHP Menu Question

    - by Vecta
    As one of the steps toward a greater website redesign I am putting the majority of the content of our website into html files to be used as includes. I am intending on passing a variable to the PHP template page through the URL to call the proper include. Our website has many programs that each need an index page as well as about 5 sub-pages. These program pages will need a menu system to navigate between the different pages.I am naming the pages pagex_1, pagex_2, pagex_3, etc. where "pagex" is descriptive of the page content. My question is, what would be the best way to handle this menu system? Is there a way to modify the initial variable used to arrive at the index page to create links in the menu to arrive at the other pages? Thanks for any help!

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