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  • Any way to make a generic List where I can add a type AND a subtype?

    - by user383178
    I understand why I cannot do the following: private class Parent { }; private class Child extends Parent { }; private class GrandChild extends Child { }; public void wontCompile(List<? extends Parent> genericList, Child itemToAdd) { genericList.add(itemToAdd); } My question is there ANY practical way to have a typesafe List where you can call add(E) where E is known to be only a Parent or a Child? I vaguely remember some use of the "|" operator as used for wildcard bounds, but I cannot find it in the spec... Thanks!

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  • What is the best solution to replace a new memory allocator in an existing code?

    - by O. Askari
    During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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  • Cast object as OleVariant in Delphi

    - by Alan Clark
    Is there a way to pass a wrap and unwrap a TObject descendent in an OleVariant? I am trying to pass a TObject across automation objects. I know it's not a good idea but I don't have a good alternative. Something like this: function GetMyObjAsVariant; var MyObj: TMyObj; begin MyObj := TMyObj.Create; result := OleVariant(MyObj); end; Which would be used by a client as var MyObj: TMyObj; begin MyObj := GetMyObjAsVariant as TMyObj; end; This fails to compile, returning E2015 Operator not applicable to this operand type.

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  • C++ / Java: Toggle boolean statement?

    - by Martijn Courteaux
    Hi, Is there a short way to toggle a boolean? With integers we can do operations like this: int i = 4; i *= 4; // equals 16 /* Which is equivalent to */ i = i * 4; So is there also something for booleans (like the *= operator for ints)? In C++: bool booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something? In Java: boolean booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something?

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  • Is call to function object inlined?

    - by dehmann
    In the following code, Foo::add calls a function via a function object: struct Plus { inline int operator()(int x, int y) const { return x + y; } }; template<class Fct> struct Foo { Fct fct; Foo(Fct f) : fct(f) {} inline int add(int x, int y) { return fct(x,y); // same efficiency adding directly? } }; Is this the same efficiency as calling x+y directly in Foo::add? In other words, does the compiler typically directly replace fct(x,y) with the actual call, inlining the code, when compiling with optimizations enabled?

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  • How do I create email addresses for all my users using my domain ([email protected])?

    - by rwain
    My client wants to create email addresses for all their dotnetnuke users using their domain. The point is to keep the user's email addresses 'private' while still allowing communication through a public email address that they can control. It's not necessary to have a full webmail interface (although that would be nice). I'm thinking it would be enough just to forward any mail on and just act as a gateway. So if an email was sent to [email protected], it would be forwarded on to the email address associated with the dotnetnuke account with username 'rwain'. Is this possible to do in a shared hosting environment? Or do I need to create some custom mail server that does a conversion of the email address and forwards it?

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  • Best way to validate currency input?

    - by Abe Miessler
    I have created the TextBox and CompareValidator below which I thought would allow input in the following forms: 5 5.00 $5.00 Unfortunately it's not allowing the version with the dollar sign in it. What is the point of doing a type check against currency if you don't allow the dollar sign? Is there a way to allow this symbol? <asp:TextBox ID="tb_CostShare" runat="server" Text='<%# Eval("CostShare", "{0:$0.00}")%>' CausesValidation="true" /> <asp:CompareValidator ID="vld_CostShare" runat="server" ControlToValidate="tb_CostShare" Operator="DataTypeCheck" Type="Currency" ValidationGroup="vld" ErrorMessage="You must enter a dollar amount for 'Cost Share'." />

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  • ActionScript: Using 'in' on protected/private variables?

    - by David Wolever
    Is there any way to mimic the in operator, but testing for the existence of protected or private fields? For example, this: <mx:Script><![CDATA[ public var pub:Boolean = true; protected var prot:Boolean = true; private var priv:Boolean = true; ]]></mx:Script> <mx:creationComplete><![CDATA[ for each (var prop in ["pub", "prot", "priv", "bad"]) trace(prop + ":", prop in this); ]]></mx:creationComplete> Will trace: pub: true prot: false priv: false bad: false When I want to see: pub: true prot: true priv: true bad: false

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  • Possible to convert list of #defines into strings (C++)

    - by brandonC
    Suppose I have a list of #defines in a header file for an external library. These #defines represent error codes returned from functions. I want to write a conversion function that can take as an input an error code and return as an output a string literal representing the actual #define name. As an example, if I have #define NO_ERROR 0 #define ONE_KIND_OF_ERROR 1 #define ANOTHER_KIND_OF_ERROR 2 I would like a function to be able to called like int errorCode = doSomeLibraryFunction(); if (errorCode) writeToLog(convertToString(errorCode)); And have convertToString() be able to auto-convert that error code without being a giant switch-case looking like const char* convertToString(int errorCode) { switch (errorCode) { case NO_ERROR: return "NO_ERROR"; case ONE_KIND_OF_ERROR: return "ONE_KIND_OF_ERROR"; ... ... ... I have a feeling that if this is possible, it would be possible using templates and metaprogramming, but that would only work the error codes were actually a type and not a bunch of processor macros. Thanks

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  • Generic Dictionary - Getting Convertion Error

    - by pm_2
    The following code is giving me an error: // GetDirectoryList() returns Dictionary<string, DirectoryInfo> Dictionary<string, DirectoryInfo> myDirectoryList = GetDirectoryList(); // The following line gives a compile error foreach (Dictionary<string, DirectoryInfo> eachItem in myDirectoryList) The error it gives is as follows: Cannot convert type 'System.Collections.Generic.KeyValuePair<string,System.IO.DirectoryInfo>' to 'System.Collections.Generic.Dictionary<string,System.IO.DirectoryInfo>’ My question is: why is it trying to perform this conversion? Can I not use a foreach loop on this type of object?

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  • How to retrieve all keys (or values) from a std::map?

    - by Owen
    This is one of the possible ways I come out: struct RetrieveKey { template <typename T> typename T::first_type operator()(T keyValuePair) const { return keyValuePair.first; } }; map<int, int> m; vector<int> keys; // Retrieve all keys transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey()); // Dump all keys copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n")); Of course, we can also retrieve all values from the map by defining another functor RetrieveValues. Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)

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  • How should I get Xcode to link an iOS project that uses a C++ static library

    - by user1681572
    Using Xcode, I've written a Cocoa Touch static library, mainly in C++. It exposes a C interface for the benefit of Objective-C client code. I have a client iOS app that uses it, and everything works and runs as expected, except that I found I needed to include a minimal .cpp file in the client project to get the link to succeed. Otherwise I get C++-related unresolved symbols, e.g. operator new(unsigned long). The above hack is easy and effective, and so I guess I'm not breaking any laws, but is there a proper way to eliminate my linker errors?

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  • C++ enum casting and templates

    - by JP
    I get the following error with VS2008: Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast) When casting a down casting a ClassA to ClassA_1 and ClassA_1 is a templated class that received an enum for parameter such as: ClassA { virtual ~ClassA(){}; } template <class Param1> ClassA_1 : public ClassA { public: //constructor ClassA_1(Param1 p1) { _p1 = p1; } Param1 _p1; } So I have a upcasted ClassA a = new ClassA_1<myenum>(); When I need to do this: ClassA_1<myenum> a1 = (ClassA_1<myenum> a); // This fails ... The only way it works is: ClassA_1<int> a1 = (ClassA_1<int> a); but this break my template as it must always deal with int... How to properly cast a enum that is now a int, back into the enum?

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  • nested list comprehension using intermediate result

    - by KentH
    I am trying to grok the output of a function which doesn't have the courtesy of setting a result code. I can tell it failed by the "error:" string which is mixed into the stderr stream, often in the middle of a different conversion status message. I have the following list comprehension which works, but scans for the "error:" string twice. Since it is only rescanning the actual error lines, it works fine, but it annoys me I can't figure out how to use a single scan. Here's the working code: errors = [e[e.find('error:'):] for e in err.splitlines() if 'error:' in e] The obvious (and wrong) way to simplify is to save the "find" result errors = [e[i:] for i in e.find('error:') if i != -1 for e in err.splitlines()] However, I get "UnboundLocalError: local variable 'e' referenced before assignment". Blindly reversing the 'for's in the comprehension also fails. How is this done? THanks. Kent

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  • Is it possible to have a variadic function in C with no non-variadic parameter?

    - by Tim
    I have the following function: void doStuff(int unusedParameter, ...) { va_list params; va_start(params, unusedParameter); /* ... */ va_end(params); } As part of a refactor, I'd like to remove the unused parameter without otherwise changing the implementation of the function. As far as I can tell, it's impossible to use va_start when you don't have a last non-variadic parameter to refer to. Is there any way around this? Background: It is in fact a C++ program, so I could use some operator-overloading magic as suggested here, but I was hoping not to have to change the interface at this point. The existing function does its work by requiring that the variable argument list be null-terminated, and scanning for the NULL, therefore it doesn't need a leading argument to tell it how many arguments it has.

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  • How do I do division on HH:MM:SS format time strings in C#?

    - by Jake
    I have a series of times that are coming to me as strings from a web service. The times are formated as HH:MM:SS:000 (3 milisecond digits). I need to compare two times to determine if one is more than twice as long as the other: if ( timeA / timeB > 2 ) What's the simplest way to work with the time strings? If I was writing in Python this would be the answer to my question: Difference between two time intervals in Python Edit: What I'm really looking for is a way to get the ratio of timeA to timeB, which requires division, not subtraction. Unfortunately, the DateTime structure doesn't appear to have a division operator. Updated the question title to reflect this.

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  • How do I search nodes of XML document for text? Or convert to SQL tables?

    - by netefficacy
    Hi I have an XML file and would like to run a search on the nodes for text that matches user input. My options are: Convert the XML file to a SQL table and run the search against the table records. Search the XML nodes themselves. The problem is that I cannot find a open source conversion utility, nor can I figure out how to search the XML nodes. I can use PHP, Ruby, or Python for the search code. Any pointers on how can I do 1 or 2? Thanks

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  • How to return a copy of the data in C++

    - by Josh Curren
    I am trying to return a new copy of the data in a C++ Template class. The following code is getting this error: invalid conversion from ‘int*’ to ‘int’. If I remove the new T then I am not returning a copy of the data but a pointer to it. template<class T> T OrderedList<T>::get( int k ) { Node<T>* n = list; for( int i = 0; i < k; i++ ) { n=n->get_link(); } return new T( n->get_data() ); // This line is getting the error ********** }

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  • Efficient way to access a mapping of identifiers in Python

    - by sixbelo
    I am writing an app to do a file conversion and part of that is replacing old account numbers with a new account numbers. Right now I have a CSV file mapping the old and new account numbers with around 30K records. I read this in and store it as dict and when writing the new file grab the new account from the dict by key. My question is what is the best way to do this if the CSV file increases to 100K+ records? Would it be more efficient to convert the account mappings from a CSV to a sqlite database rather than storing them as a dict in memory?

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  • How to add javascript to YII correctly?

    - by RD.
    I want to create several javascript function that will be needed on different pages. Most will be relevant only to one page, but some to several. I know if I add general conversion functions, it would be a good idea to just create a new javascript file and put all these generic functions into that one file. Bringing me to my first question: Where would you store the generic javascript file? In "protected"? Which subfolder? Then, I need to address the placement of other javascript code. If I have javascript that will only be used on one page, should I use this technique or should I stick to a similar approach as above? The emphasis is on doing it correctly. I want to fall exactly in line with the yii framework.

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  • How do I iterate over a tuple

    - by Caligo
    How can I iterate over a tuple starting from, say, index 1 to 2? The following doesn't work. using boost::fusion::cons; typedef cons<A, cons<B, cons<C, cons<D> > > > MyTuple; MyTuple tuple_; template <class T> struct DoSomething{ DoSomething(T& t) : t_(&t){ } template <class U> void operator()(U u){ boost::fusion::at<mpl::int_<u> >(*t_); } T* t_; }; boost::mpl::for_each< boost::mpl::range_c<int, 1, 3> >( DoSomething<MyTuple>(tuple_) );

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  • C++: use array of strings wrapped in namespace?

    - by John D.
    I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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  • formatting and converting in java

    - by mike_hornbeck
    I have few small basic problems : How to format : int i = 456; to give output : ""00000456" ? I've tried %08d but it's not working. Next thing is a problem with conversion and then formatting. I have side and height of triangle, let's say int's 4,7, and 7 is the height. From formula for field we know that F=1/2(a*h). So how to get F as float, with precision up to 10 places ? float f = a*h; works fine, but multiplying it by 0.5 gives error and by 1/2 returns 0.

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  • How does the stream manipulators work?

    - by Narek
    It is well known that the user can define stream manipulators like this: ostream& tab(ostream & output) { return output<< '\t'; } And this can be used in main() like this: cout<<'a'<<tab<<'b'<<'c'<<endl; Please explain me how does this all work? If operator<< assumes as a second parameter a pointer to the function that takes and returns ostream &, then please explain my why it is necessary? What would be wrong if the function does not take and return ostream & but it was void instead of ostream &? Also it is interesting why “dec”, “hex” manipulators take effect until I don’t change between them, but user defined manipulators should be always used in order to take effect for each streaming?

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  • How to stable_sort without copying?

    - by Mehrdad
    Why does stable_sort need a copy constructor? (swap should suffice, right?) Or rather, how do I stable_sort a range without copying any elements? #include <algorithm> class Person { Person(Person const &); // Disable copying public: Person() : age(0) { } int age; void swap(Person &other) { using std::swap; swap(this->age, other.age); } friend void swap(Person &a, Person &b) { a.swap(b); } bool operator <(Person const &other) const { return this->age < other.age; } }; int main() { static size_t const n = 10; Person people[n]; std::stable_sort(people, people + n); }

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