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  • Why isn't the compiler smarter in this const function overloading problem?

    - by Frank
    The following code does not compile: #include <iostream> class Foo { std::string s; public: const std::string& GetString() const { return s; } std::string* GetString() { return &s; } }; int main(int argc, char** argv){ Foo foo; const std::string& s = foo.GetString(); // error return 0; } I get the following error: const1.cc:11: error: invalid initialization of reference of type 'const std::string&' from expression of type 'std::string* It does make some sense because foo is not of type const Foo, but just Foo, so the compiler wants to use the non-const function. But still, why can't it recognize that I want to call the const GetString function, by looking at the (type of) variable I assign it to? I found this kind of surprising.

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  • How can I port msvc++ code with non-dependent names in templates to Linux?

    - by user352382
    I can deal with porting platform dependent functions. I have a problem that the compilers I tried on Linux (clang and g++) do not accept the following code, while the msvc++ compiler does: template <class T> class Base { protected: T Value; }; template <class T> class Derived : public Base<T> { public: void setValue(const T& inValue){ Value = inValue; } }; int main(int argc, char const *argv[]) { Derived<int> tmp; tmp.setValue(0); return 0; } g++ error: main.cpp: In member function ‘void Derived<T>::setValue(const T&)’: main.cpp:11:3: error: ‘Value’ was not declared in this scope I believe this due to the use of a non-dependent name (Value) in the second class. More information. The problem is that I have a very large code base, in which this type of code is used very often. I understand that it is wrong when looking at the standard. However it is very convenient not having to write this-> or Base<T>:: in front of every use of Value. Even writing using Base<T>::Value; at the start of the derived class is problematic when you use ~20 members of the base class. So my question is: are there compilers for Linux that allow this kind of code (with or without extra compiler switches)? Or are there small modifications that will allow this code to compile on Linux?

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  • Scope quandary with namespaces, function templates, and static data

    - by Adrian McCarthy
    This scoping problem seems like the type of C++ quandary that Scott Meyers would have addressed in one of his Effective C++ books. I have a function, Analyze, that does some analysis on a range of data. The function is called from a few places with different types of iterators, so I have made it a template (and thus implemented it in a header file). The function depends on a static table of data, AnalysisTable, that I don't want to expose to the rest of the code. My first approach was to make the table a static const inside Analysis. namespace MyNamespace { template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { static const int AnalysisTable[] = { /* data */ }; ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace It appears that the compiler creates a copy of AnalysisTable for each instantiation of Analyze, which is wasteful of space (and, to a small degree, time). So I moved the table outside the function like this: namespace MyNamespace { const int AnalysisTable[] = { /* data */ }; template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace There's only one copy of the table now, but it's exposed to the rest of the code. I'd rather keep this implementation detail hidden, so I introduced an unnamed namespace: namespace MyNamespace { namespace { // unnamed to hide AnalysisTable const int AnalysisTable[] = { /* data */ }; } // unnamed namespace template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace But now I again have multiple copies of the table, because each compilation unit that includes this header file gets its own. If Analyze weren't a template, I could move all the implementation detail out of the header file. But it is a template, so I seem stuck. My next attempt was to put the table in the implementation file and to make an extern declaration within Analyze. // foo.h ------ namespace MyNamespace { template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { extern const int AnalysisTable[]; ... // implementation uses AnalysisTable return result; } } // namespace MyNamespace // foo.cpp ------ #include "foo.h" namespace MyNamespace { const int AnalysisTable[] = { /* data */ }; } This looks like it should work, and--indeed--the compiler is satisfied. The linker, however, complains, "unresolved external symbol AnalysisTable." Drat! (Can someone explain what I'm missing here?) The only thing I could think of was to give the inner namespace a name, declare the table in the header, and provide the actual data in an implementation file: // foo.h ----- namespace MyNamespace { namespace PrivateStuff { extern const int AnalysisTable[]; } // unnamed namespace template <typename InputIterator> int Analyze(InputIterator begin, InputIterator end) { ... // implementation uses PrivateStuff::AnalysisTable return result; } } // namespace MyNamespace // foo.cpp ----- #include "foo.h" namespace MyNamespace { namespace PrivateStuff { const int AnalysisTable[] = { /* data */ }; } } Once again, I have exactly one instance of AnalysisTable (yay!), but other parts of the program can access it (boo!). The inner namespace makes it a little clearer that they shouldn't, but it's still possible. Is it possible to have one instance of the table and to move the table beyond the reach of everything but Analyze?

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  • Django templates crashes with no sense

    - by user233323
    Hello I'm trying to use google visualization API along with django templates system. I got an error that don't know how to fix. The error is the following: invalid_block_tag raise self.error(token, "Invalid block tag: '%s'" % command) django.template.TemplateSyntaxError: Invalid block tag: 'endfor' The code is: function drawChart() { var data = new google.visualization.DataTable(); data.addColumn('date', 'time'); data.addColumn('number', 'x'); data.addColumn('number', 'y'); data.addColumn('number', 'z'); data.addRows([ {% for d in datos &} [new Date({{d.instante|date:"Y, m, d, H, i, s"}}), {{d.x}}, {{d.y}}, {{d.z}}] {% if not forloop.last %},{% endif %} ]); {% endfor %} var chart = new google.visualization.AnnotatedTimeLine(document.getElementById('chart_div')); chart.draw(data, {displayAnnotations: true}); } Thanks you all!

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  • Generate Visual Studio Project Templates with CruiseControl.Net or MSBuild

    - by Daniel A. White
    Hey all. I have a working workflow in CruiseControl.Net that successfully builds and tests an MSBuild project that is calling my Visual Studio 2010 solution. How do I create Visual Studio project templates in either CruiseControl.Net or with MSBuild? The build server does not have Visual Studio 2010 installed. Thanks for your time! Note: This can be extended to any other solution that could be scripted with a batch as well, but I cannot install Visual Studio 2010 on the machine.

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  • GAE/Django Templates (0.96) filters to get LENGTH of GqlQuery and filter it

    - by Halst
    I pass the query with comments to my template: COMM = CommentModel.gql("ORDER BY created") doRender(self,CP.template,{'CP':CP,'COMM':COMM, 'authorize':authorize()}) And I want to output the number of comments as a result, and I try to do things like that: <a href="...">{{ COMM|length }} comments</a> Thats does not work (yeah, since COMM is GqlQuery, not a list). What can I do with that? Is there a way to convert GqlQuery to list or is there another solution? (first question) Second question is, how to filter this list in template? Is there a construct like this: <a href="...">{{ COMM|where(reference=smth)|length }} comments</a> so that I can get not only the number of all comments, but only comments with certain db.ReferenceProperty() property, for example. Last question: is it weird to do such things using templates?

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  • POI dynamic templates

    - by gabriela
    Hello, Can anyone tell me where do I find some useful documentation on handling copying rows, cells, columns from one excel file to another, using POI? I need to insert in one blank excel file, 2 or more templates from other files, dynamic. I also need to keep all the styles made for the group of cells that I copy. How can I do that? Nothing found on apache poi tutorial on this point. I am using POI 3.0.1. Thank you!

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  • How to use two templates for ListViewItem using WPF

    - by Gregor
    Hi, I would like to have a ListView that would have have items similar to Microsoft Outlook inbox with items arranged by Conversations (see the attached photo). An item can either be a simple textblock containing the topic of the conversation (on the photo this are the blue lines) or it can contain email information specified by the ListView's header. It would be best if the items with conversation topics would be push buttons so that emails inside that conversation could be shown or hidden by pressing this button. Any ideas how can I achieve this? Do I specify two ListViewItem templates? If yes, how do I tell in the code which template to use for each item? Any help will be GREATLY appreciated!! Regards, Gregor

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  • Missing templates after re-installing VS 2008

    - by ray247
    I installed VS 2008 and I installed .NET 3.5 SP1 and I got all templates. Then, I had to uninstall VS 2008 (please don't ask why) without uninstalling .NET Framework 3.5 SP1 or anything else. After that, I re-installed VS 2008 back, then I open up VS 2008 and found that when I add a new item the Entity Framework template is not among the list anymore. Could someone please help on how to resolve this problem? Thank you so much! Ray.

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  • C++ Templates: implicit conversion, no matching function for call to ctor

    - by noname
    template<class T> class test { public: test() { } test(T& e) { } }; int main() { test<double> d(4.3); return 0; } Compiled using g++ 4.4.1 with the following errors: g++ test.cpp -Wall -o test.exe test.cpp: In function 'int main()': test.cpp:18: error: no matching function for call to 'test<double>::test(double) ' test.cpp:9: note: candidates are: test<T>::test(T&) [with T = double] test.cpp:5: note: test<T>::test() [with T = double] test.cpp:3: note: test<double>::test(const test<double>&) make: *** [test.exe] Error 1 However, this works: double a=1.1; test<double> d(a); Why is this happing? Is it possible that g++ cannot implicitly convert literal expression 1.1 to double? Thanks.

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  • can these templates be made unambiguous

    - by R Samuel Klatchko
    I'm trying to create a set of overloaded templates for arrays/pointers where one template will be used when the compiler knows the size of the array and the other template will be used when it doesn't: template <typename T, size_t SZ> void moo(T (&arr)[SZ]) { ... } template <typename T> void moo(T *ptr) { ... } The problem is that when the compiler knows the size of the array, the overloads are ambiguous and the compile fails. Is there some way to resolve the ambiguity (perhaps via SFINAE) or is this just not possible.

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  • Design Web Templates

    - by Pradeep
    Hi, I am a PHP, VB.NET programmer and i like to build websites. I am good at coding but have never done website designing. Please suggest me some good study resource on Photoshop and flash website design. I have recently made few templates on photoshop but don't know how to code them for valid HTML-CSS. Please let me know which is the best method to design website template e.g. Photoshop, DreamWeaver etc. Also provide links to good study and practice resource for the same. Thanks in advance.

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  • Not work variables in django templates

    - by ??????? ???????
    My context dictionary not sending to my templates. I have function from django.shortcuts import render_to_response def home(request): return render_to_response('home.html',{'test':'test'}) and i have simple template such as: <html> <body> my test == {{test}} </body> </html> When i open my site in browser, i have "my test == ". settings.py is default. I dont use something custom. What the problem? Server is apache with wsgi module.

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  • Where are the function literals in c++?

    - by academicRobot
    First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens). The idea is that when you make a conventional function call, it compiles to something like this: callq <immediate address> But if you make a function call using a function pointer, it compiles to something like this: mov <memory location>,%rax callq *%rax Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to template <int int_literal> struct my_template {...};` I'd like to write template <func_literal_t func_literal> struct my_template {...}; and have calls to func_literal within my_template compile to callq <immediate address>. Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language? Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications. It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder. p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.

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  • Question regarding C++ Templates

    - by Isuru
    I used a simple class for a test program about templates, this is what I did: template <typename T> class test { public: test<T>::test(); T out(); }; template <typename T> test<T>::test() { } T test<T>::out() { } int main() { //test<int> t; } But when I try to compile it says 'T' : undeclared identifier and use of class template requires template argument list , pointing to the same line, where I have implemented the method out() . Can anyone please explain what the problem is?? I'm using visual studio 2008.

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  • Can I move the order of XCode, Cocoa, and User Templates around in XCode 3.1?

    - by Warren P
    I followed the other questions on StackOverflow and made custom User Templates. Instead of replacing the factory default Cocoa class template, I have to pick a new user template. The order that is shown in XCode's New File dialog box is: iPhone templates first (great if you mostly do iphone development) Second the User templates Third the default Mac OS templates. I want my user stuff first, Mac OS templates second, and I want to bury iPhone templates in third and last place. The sort is obviously not alphabetical. And you can't drag/drop reorder. (At least not in xcode 3.1.3)? From stackoverflow

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  • Template function as a template argument

    - by Kos
    I've just got confused how to implement something in a generic way in C++. It's a bit convoluted, so let me explain step by step. Consider such code: void a(int) { // do something } void b(int) { // something else } void function1() { a(123); a(456); } void function2() { b(123); b(456); } void test() { function1(); function2(); } It's easily noticable that function1 and function2 do the same, with the only different part being the internal function. Therefore, I want to make function generic to avoid code redundancy. I can do it using function pointers or templates. Let me choose the latter for now. My thinking is that it's better since the compiler will surely be able to inline the functions - am I correct? Can compilers still inline the calls if they are made via function pointers? This is a side-question. OK, back to the original point... A solution with templates: void a(int) { // do something } void b(int) { // something else } template<void (*param)(int) > void function() { param(123); param(456); } void test() { function<a>(); function<b>(); } All OK. But I'm running into a problem: Can I still do that if a and b are generics themselves? template<typename T> void a(T t) { // do something } template<typename T> void b(T t) { // something else } template< ...param... > // ??? void function() { param<SomeType>(someobj); param<AnotherType>(someotherobj); } void test() { function<a>(); function<b>(); } I know that a template parameter can be one of: a type, a template type, a value of a type. None of those seems to cover my situation. My main question is hence: How do I solve that, i.e. define function() in the last example? (Yes, function pointers seem to be a workaround in this exact case - provided they can also be inlined - but I'm looking for a general solution for this class of problems).

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  • Django dictionary in templates: Grab key from another objects attribute

    - by Jordan Messina
    I have a dictionary called number_devices I'm passing to a template, the dictionary keys are the ids of a list of objects I'm also passing to the template (called implementations). I'm iterating over the list of objects and then trying to use the object.id to get a value out of the dict like so: {% for implementation in implementations %} {{ number_devices.implementation.id }} {% endfor %} Unfortunately number_devices.implementation is evaluated first, then the result.id is evaluated obviously returning and displaying nothing. I can't use parentheses like: {{ number_devices.(implementation.id) }} because I get a parse error. How do I get around this annoyance in Django templates? Thanks for any help!

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  • How do I compile variadic templates conditionally?

    - by FredOverflow
    Is there a macro that tells me whether or not my compiler supports variadic templates? #ifdef VARIADIC_TEMPLATES_AVAILABLE template<typename... Args> void coolstuff(Args&&... args); #else ??? #endif If they are not supported, I guess I would simulate them with a bunch of overloads. Any better ideas? Maybe there are preprocessor libraries that can ease the job?

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  • Polymorphic classes in templates

    - by soxarered
    Let's say we have a class hierarchy where we have a generic Animal class, which has several classes directly inherit from it (such as Dog, Cat, Horse, etc..). When using templates on this inheritance hierarchy, is it legal to just use SomeTemplateClass<Animal> and then shove in Dogs and Cats and Horses into this templated object? For example, assume we have a templated Stack class, where we want to host all sorts of animals. Can I simply state Stack<Animal> s; Dog d; s.push(d); Cat c; s.push(c);

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  • Where are the function literals c++?

    - by academicRobot
    First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens). The idea is that when you make a conventional function call, it compiles to something like this: callq <immediate address> But if you make a function call using a function pointer, it compiles to something like this: mov <memory location>,%rax callq *%rax Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to template <int int_literal> struct my_template {...};` I'd like to write template <func_literal_t func_literal> struct my_template {...}; and have calls to func_literal within my_template compile to callq <immediate address>. Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language? Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications. It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder. p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.

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  • Using Django view variables inside templates

    - by William
    Hi, this is a rather basic question (I'm new to Django) but I'm having trouble using a variable set in my view inside my template. If I initialize a string or list inside my view (i.e. h = "hello") and then attempt to call it inside a template: {{ h }} there is neither output nor errors. Similarly, if I try to use a variable inside my template that doesn't exist: {{ asdfdsadf }} there is again no error reported. Is this normal? And how can I use my variables within my templates. Thanks!

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  • Pass a function as parameter in jQuery?

    - by thedp
    Hello, I would like to pass to a jQuery function a regular function, instead of the usual anonymous function, but I'm not sure how such a thing could be done. Instead of this: function setVersion(feature) { $.post("some.php", { abc:"abc" }, function(data){ // do something here }, "json"); } I would like to do this: function foo(data){ // do something here } function setVersion(feature) { $.post("some.php", { abc:"abc" }, foo, "json"); } Thank you.

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  • C++ templates - matrix class

    - by lastOfMohicans
    Hi I'm learning templates in C++ so I decied to write matrix class which would be a template class. In Matrix.h file I wrote #pragma once #include "stdafx.h" #include <vector> using namespace std; template<class T> class Matrix { public: Matrix(); ~Matrix(); GetDataVector(); SetDataVector(vector<vector<T>> dataVector); bool operator == (Matrix* matrix); bool operator < (Matrix* matrix); bool operator <= (Matrix* matrix); bool operator > (Matrix* matrix); bool operator >= (Matrix* matrix); Matrix* operator + (Matrix* matrix); Matrix* operator - (Matrix* matrix); Matrix* operator * (Matrix* matrix); private: vector<vector<T>> datavector; int columns,rows; }; In Matrix cpp Visual Stuio automaticlly generated code for default constructors #include "StdAfx.h" #include "Matrix.h" Matrix::Matrix() { } Matrix::~Matrix() { } However if I want to compile this I get an error 'Matrix' : use of class template requires template argument list The error are in file Matrix.cpp in default constructors What may be the problem ??

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