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  • Is there any difference these two pieces of code?

    - by Poiuyt
    #include<stdio.h> class A {public: int a; }; class B: public A {private: int a;}; int main(){ B b; printf("%d", b.a); return 0; } #include<stdio.h> class A {public: int a; }; class B: private A {}; int main(){ B b; printf("%d", b.a); return 0; } I ask because I get different errors: error: 'int B::a' is private error: 'int A::a' is inaccessible Apart from what the errors might reveal, is there any difference at all in the behaviour of these two pieces of code?

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  • Avoiding instanceof in Java

    - by Mark Lutton
    Having a chain of "instanceof" operations is considered a "code smell". The standard answer is "use polymorphism". How would I do it in this case? There are a number of subclasses of a base class; none of them are under my control. An analogous situation would be with the Java classes Integer, Double, BigDecimal etc. if (obj instanceof Integer) {NumberStuff.handle((Integer)obj);} else if (obj instanceof BigDecimal) {BigDecimalStuff.handle((BigDecimal)obj);} else if (obj instanceof Double) {DoubleStuff.handle((Double)obj);} I do have control over NumberStuff and so on. I don't want to use many lines of code where a few lines would do. (Sometimes I make a HashMap mapping Integer.class to an instance of IntegerStuff, BigDecimal.class to an instance of BigDecimalStuff etc. But today I want something simpler.) I'd like something as simple as this: public static handle(Integer num) { ... } public static handle(BigDecimal num) { ... } But Java just doesn't work that way. I'd like to use static methods when formatting. The things I'm formatting are composite, where a Thing1 can contain an array Thing2s and a Thing2 can contain an array of Thing1s. I had a problem when I implemented my formatters like this: class Thing1Formatter { private static Thing2Formatter thing2Formatter = new Thing2Formatter(); public format(Thing thing) { thing2Formatter.format(thing.innerThing2); } } class Thing2Formatter { private static Thing1Formatter thing1Formatter = new Thing1Formatter(); public format(Thing2 thing) { thing1Formatter.format(thing.innerThing1); } } Yes, I know the HashMap and a bit more code can fix that too. But the "instanceof" seems so readable and maintainable by comparison. Is there anything simple but not smelly?

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  • String manipulation appears to be inefficient

    - by user2964780
    I think my code is too inefficient. I'm guessing it has something to do with using strings, though I'm unsure. Here is the code: genome = FASTAdata[1] genomeLength = len(genome); # Hash table holding all the k-mers we will come across kmers = dict() # We go through all the possible k-mers by index for outer in range (0, genomeLength-1): for inner in range (outer+2, outer+22): substring = genome[outer:inner] if substring in kmers: # if we already have this substring on record, increase its value (count of num of appearances) by 1 kmers[substring] += 1 else: kmers[substring] = 1 # otherwise record that it's here once This is to search through all substrings of length at most 20. Now this code seems to take pretty forever and never terminate, so something has to be wrong here. Is using [:] on strings causing the huge overhead? And if so, what can I replace it with? And for clarity the file in question is nearly 200mb, so pretty big.

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  • C++ Template Classes and Copy Construction

    - by themoondothshine
    Is there any way I can construct an new object from the given object if the template parameters of both objects are identical at run-time? For example: I have a template class with the declaration: template<typename _Type1, typename _Type2> class Object; Next, I have two instantiations of the template: template class Object<char, int>; template class Object<wchar_t, wint_t>; Now, I want to write a member function such as: template<typename _Type1, typename _Type2> Object<char, int> Object<_Type1, _Type2>::toCharObject() { if(__gnu_cxx::__are_same<_Type1, char>::__value) return *this; else { //Perform some kind of conversion and return an Object<char, int> } } I have tried a couple of techniques, such as using __gnu_cxx::__enable_if<__gnu_cxx::__are_same<_Type1, char>::__value, _Type1>::__type in a copy constructor for the Oject class, but I keep running into the error: error: conversion from ‘Object<wchar_t, wint_t>’ to non-scalar type ‘Object<char, int>’ requested Is there no way I can do this? Any help will be greatly appreciated!

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  • C++ compile time polymorphism doubt ?

    - by user313921
    Below program contains two show() functions in parent and child classes, but first show() function takes FLOAT argument and second show() function takes INT argument. .If I call show(10.1234) function by passing float argument, it should call class A's show(float a) function , but it calls class B's show(int b). #include<iostream> using namespace std; class A{ float a; public: void show(float a) { this->a = a; cout<<"\n A's show() function called : "<<this->a<<endl; } }; class B : public A{ int b; public: void show(int b) { this->b = b; cout<<"\n B's show() function called : "<<this->b<<endl; } }; int main() { float i=10.1234; B Bobject; Bobject.show((float) i); return 0; } Output: B's show() function called : 10 Expected output: A's show() function called : 10.1234 Why g++ compiler chosen wrong show() function i.e class B's show(int b) function ?

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  • static_cast from Derived* to void* to Base*

    - by Roberto
    I would like to cast a pointer to a member of a derived class to void* and from there to a pointer of the base class, like in the example below: #include <iostream> class Base { public: void function1(){std::cout<<"1"<<std::endl;} virtual void function2()=0; }; class Derived : public Base { public: virtual void function2(){std::cout<<"2"<<std::endl;} }; int main() { Derived d; void ptr* = static_cast<void*>(&d); Base* baseptr=static_cast<Base*>(ptr); baseptr->function1(); baseptr->function2(); } This compiles and gives the desired result (prints 1 and 2 respectively), but is it guaranteed to work? The description of static_cast I found here: http://en.cppreference.com/w/cpp/language/static_cast only mentions conversion to void* and back to a pointer to the same class (point 10).

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  • Does Java have "properties" that work the same way properties work in C# (see the body of my text)?

    - by tyrone302
    In C#, you can use properties to make a data field publicly accessible (allowing the user to directly access it), and yet retain the ability to perform data validation on those directly-accessed fields. Doese Java have something similar? For Instance, suppose there exists a C# class with the following implementation(see below): public class newInt{ public newInt(){...} public int x{ get{ return this.x } set{ this.x = isValid(value) } } } private static int isValid(int value){...} This definition in the class allows the user to "naturally" use the data field 'x' when retrieving values from it and assigning values to it. Below is how it would be used in main. public class Test{ public static void main(String[] args){ newInt a = new newInt(); a.x = 50; int b = a.x; } } The question is... can java do this as well? if so, what is it called?

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  • C++ Template Usage

    - by MalcomTucker
    If I have a template definition like the one below, can someone provide a code sample for how I would actually instantiate an instance of this with two of my own classes? template <class T1, class T2> class LookUpTable { public: LookUpTable(); void set(Tl x, T2* y); T2* get(Tl x); }; Thanks.

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  • OverRiding Help

    - by user445714
    Few questions on over riding. I am interiting a method openRead from another class, the method is to be overridden so that the scanner class uses the provided delimiter pattern, which is referenced. I need to make use of the scanner class useDelmiter method method from another class [code] public boolean openRead() throws FileNotFoundException { sc = new Scanner(new File(fileName)); if (fileName != null) { return true; } else { return false; } } [/code] delimiter [code] protected final String DELIMITERS = "[\s[^'a-zA-Z]]"; [/code] I'm at a loss to how i over ride this using the constant delimiter.

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  • (Strange) C++ linker error in constructor

    - by Microkernel
    I am trying to write a template class in C++ and getting this strange linker error and can't figureout the cause, please let me know whats wrong with this! Here is the error message I am getting in Visula C++ 2010. 1>------ Rebuild All started: Project: FlashEmulatorTemplates, Configuration: Debug Win32 ------ 1> main.cpp 1> emulator.cpp 1> Generating Code... 1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall flash_emulator<char>::flash_emulator<char>(char const *,struct FLASH_PROPERTIES *)" (??0?$flash_emulator@D@@QAE@PBDPAUFLASH_PROPERTIES@@@Z) referenced in function _main 1>C:\Projects\FlashEmulator_templates\VS\FlashEmulatorTemplates\Debug\FlashEmulatorTemplates.exe : fatal error LNK1120: 1 unresolved externals ========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ========== Error message in g++ main.cpp: In function âint main()â: main.cpp:8: warning: deprecated conversion from string constant to âchar*â /tmp/ccOJ8koe.o: In function `main': main.cpp:(.text+0x21): undefined reference to `flash_emulator<char>::flash_emulator(char*, FLASH_PROPERTIES*)' collect2: ld returned 1 exit status There are 2 .cpp files and 1 header file, and I have given them below. emulator.h #ifndef __EMULATOR_H__ #define __EMULATOR_H__ typedef struct { int property; }FLASH_PROPERTIES ; /* Flash emulation class */ template<class T> class flash_emulator { private: /* Private data */ int key; public: /* Constructor - Opens an existing flash by name flashName or creates one with given FLASH_PROPERTIES if it doesn't exist */ flash_emulator( const char *flashName, FLASH_PROPERTIES *properties ); /* Constructor - Opens an existing flash by name flashName or creates one with given properties given in configFIleName */ flash_emulator<T>( char *flashName, char *configFileName ); /* Destructor for the emulator */ ~flash_emulator(){ } }; #endif /* End of __EMULATOR_H__ */ emulator.cpp #include <Windows.h> #include "emulator.h" using namespace std; template<class T>flash_emulator<T>::flash_emulator( const char *flashName, FLASH_PROPERTIES *properties ) { return; } template<class T>flash_emulator<T>::flash_emulator(char *flashName, char *configFileName) { return; } main.cpp #include <Windows.h> #include "emulator.h" int main() { FLASH_PROPERTIES properties = {0}; flash_emulator<char> myEmulator("C:\newEMu.flash", &properties); return 0; }

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  • Drupal 6, how to identify active menu item by url parameters (full link), ?q=page1&filter=10

    - by OlgaV
    I have a submenu that has all items linked to the same node, but with different additional parameters, for ex: ... <li...><a href = "/?q=page1&filter=10" class = "... active">Item1</a></li> <li...><a href = "/?q=page1&filter=11" class = "... active">Item2</a></li> ... in this case all items have class 'active' and none of them has class 'active-trail'. Is there any way to identify the true active link (for styling purposes)? any suggestions will be much appreciated!

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  • Friendly way to override `const`-overloaded member function?

    - by xtofl
    Given a base class class A { int i; public: int& f(){ return i;} const int& f() const { return i;} }; And a sub class class ConstA : private A { public: const int& f() const { return A::f(); } }; Is there a wrist-friendly way to access the ConstA::f method on a non-const variable? ConstA ca; int i = ca.f(); // compile error: int& A::f() is not accessible since A is privately inherited int j = static_cast<const ConstA&>(ca).f(); // this works, but it hurts a little... Or is it so ugly since hiding A::f generally is a bad idea, violating the Liskov Substitution Principle: any subclass of A must at least be capable of all A's functionality? void set( A& a, int i ) { a.f() = i; } class ConstA2 : public A { private: int& f(){ return A::f(); } }; ConstA2 ca2; set( ca2, 1 ); (Note: this question popped up while thinking about this question)

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  • how to declare object variable name in loop

    - by user3717895
    public class Node{ Node p,l,r; int height; String s; { /** class body**/ } } String[] S=new String[5000]; int i=0; while (i<5000){ Node x=new Node(); x=S[i]; } I want to make 5000 Node object. above code assign same variable name x every time but i want different variable name . then how to declare 5000 class variable name without declaring it manually. is there something by which i can create 5000 Node class object with ease.

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  • Multiple Packages in an Android App

    - by stormin986
    I am including a class in my app that another developer has made freely available. His class has a different package. Will this cause any issues on Android, the market, etc? Does every single class in the app need to be my own package?

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  • programming help

    - by user208639
    class Person holds personal data Its constructor receives 3 parameters, two Strings representing first and last names and an int representing age public Person(String firstName, String lastName, int age) { its method getName has no parameters and returns a String with format "Lastname, Firstname" its method getAge takes no parameters and returns an int representing the current age its method birthday increases age value by 1 and returns the new age value Create the class Person and paste the whole class into the textbox below public class Person { public Person(String first, String last, int age) { getName = "Lastname, Firstname"; System.out.print(last + first); getAge = age + 1; return getAge; System.out.print(getAge); birthday = age + 1; newAge = birthday; return newAge; } } im getting errors such as "cannot find symbol - variable getName" but when i declare a variable it still not working, i also wanted to ask if i am heading in the right direction or is it all totally wrong? im using a program called BlueJ to work on.

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  • redefinition c++

    - by coubeatczech
    hi, how does header including in c++ work? I have the classes already implemented in .h file and when there is #include in two files, there's this error: files.h:14:7: error: redefinition of ‘class abstract_file’ files.h:14:20: error: previous definition of ‘class abstract_file’ multiple times for each class and enum. Can anyone explain this?

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  • Delete rows out of table that is innerjoined and unioned with 2 others

    - by jonathan
    We have 3 tables (table1, table2, table3), and I need to delete all the rows from table1 that have the same ID in table2 OR table3. To see a list of all of these rows I have this code: ( select table2.ID, table2.name_first, table2.name_last, table2.Collected from table2 inner join table1 on table1.ID = table2.ID where table2.Collected = 'Y' ) union ( select table3.ID, table3.name_first, table3.name_last, table3.Collected from table3 inner join table1 on table1.ID = table3.ID where table3.Collected = 'Y' ) I get back about 200 rows. How do I delete them from table1? I don't have a way to test if my query will work, so I'm nervous about modifying something I found online and potentially deleting data (we do have backups, but I'd rather not test out their integrity). TIA!

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  • jQuery - Traversing the DOM

    - by danit
    Here is my HTML: <li> <div class="menu_inner"> <a href="#"> <div class="button"><img class="486" src="images/portalbutton.png" /></div> <div class="prod_description">&nbsp;</div> </a> </div> </li> I want to add a .click() function to .prod_description, the click event should take the background colour applied in CSS from the li element. Using this code: $(".prod_description").mousedown(function() { $('#toolbar').css('background-color', $(this).parent().css('background-color')) }) I dont seem to be able to get the correct $(this).parent() combination....

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  • Should I implement IDisposable here?

    - by dotnetdev
    My method which calls SQL Server returns a datareader but because of what I need to do (return the datareader to the calling method which is in page code-behind), I can't close the connection in the class of the method which calls sql server, so I have no finally or using blocks. Is the correct way of disposing resources to make the class implement IDisposable? Or from the caller, explicitly dispose the unmanged resource (class-level fields)? Thanks

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  • Force the use of interface instead of concrete implementation in declaration (.NET)

    - by gammelgul
    In C++, you can do the following: class base_class { public: virtual void do_something() = 0; }; class derived_class : public base_class { private: virtual void do_something() { std::cout << "do_something() called"; } }; The derived_class overrides the method do_something() and makes it private. The effect is, that the only way to call this method is like this: base_class *object = new derived_class(); object->do_something(); If you declare the object as of type derived_class, you can't call the method because it's private: derived_class *object = new derived_class(); object->do_something(); // --> error C2248: '::derived_class::do_something' : cannot access private member declared in class '::derived_class' I think this is quite nice, because if you create an abstract class that is used as an interface, you can make sure that nobody accidentally declares a field as the concrete type, but always uses the interface class. Since in C# / .NET in general, you aren't allowed to narrow the access from public to private when overriding a method, is there a way to achieve a similar effect here?

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  • php: avoiding __get in certain circumstances?

    - by user151841
    I have a class where I'm using __set. Because I don't want it to set just anything, I have an array of approved variables that it checks before it will actually set a class property. However, on construct, I want the __construct method to set several class properties, some of which are not in the approved list. So when construct happens, and I do $this->var = $value, I of course get my exception that I'm not allowed to set that variable. Can I get around this somehow?

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  • complex data requirement.

    - by Abulalia
    Here is my query: select Table1.a, Table1.b, Table1.c, Table1.d, Table2.e, Table3.f, Table4.g, Table5.h from Table1 left join Table6 on Table1.b=Table6.b left join Table3 on Table6.j=Table3.j left join Table7 on Table1.b=Table7.b left join Table5 on Table7.h=Table5.h inner join Table4 on Table1.k=Table4.k inner join Table2 on Table1.m=Table2.m where Table2.e <= x and Table2.n = y and Table3.f in (‘r’, ‘s’) and Table1.d = z group by Table1.a, Table1.b, Table1.c, Table1.d, Table2.e, Table3.f, Table4.g, Table5.h order by Table1.a, Table1.b, Table1.c I am looking for records (a,b,c,d,e,f,g,h) for every a when the very first record b (there are multiple records b for each a) is either 'r' or 's'. Can someone help?

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