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  • C++ template specialization

    - by user231536
    I have a class template <typename T> class C { static const int K=1; static ostream& print(ostream& os, const T& t) { return os << t;} }; I would like to specialize C for int. //specialization for int template <> C<int>{ static const int K=2; } I want the default print method that works for int to remain and just change the constant. For some specializations, I want to keep K=1 and change the print method because there is no << operator. How do I do this?

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  • typedef to store pointers in C

    - by seriouslion
    The Size of pointer depends on the arch of the machine. So sizeof(int*)=sizeof(int) or sizeof(int*)=sizeof(long int) I want to have a custom data type which is either int or long int depending on the size of pointer. I tried to use macro #if, but the condition for macros does not allow sizeof operator. Also when using if-else, typedef is limited to the scope of if. if((sizeof(int)==sizeof(int *)){ typedef int ptrtype; } else{ typedef long int ptrtype; } //ptrtype not avialble here Is there any way to define ptrtype globally?

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  • What is the difference between "a is b" and "id(a) == id(b)" in Python?

    - by bp
    The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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  • Double "!!" in Ruby [closed]

    - by Alex Maslakov
    Possible Duplicate: What does !! mean in ruby? Ruby, !! operator (a/k/a the double-bang) Sometimes I see a Ruby code like this def sent? !!@sent_at end It seems to be not logical. Is it necessary to use here double !? As far as I'm concerned, it might be just def sent? @sent_at end UPDATE: then what is the difference between these def sent? !!@sent_at end def sent? @sent_at.nil? end def sent? @sent_at == nil end

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  • partial string matching - R

    - by DonDyck
    I need to write a query in R to match partial string in column names. I am looking for something similar to LIKE operator in SQL. For e.g, if I know beginning, middle or end part of the string I would write the query in format: LIKE 'beginning%middle%' in SQL and it would return matching strings. In pmatch or grep it seems I can only specify 'beginning' , 'end' and not the order. Is there any similar function in R that I am looking for? For example, say I am looking in the vector: y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking") Lets say I want to write a query which picks "looking for a new dog" and I know start of the string is "looking" and end of string is "dog". If I do a grep("dog",y) it will return 1,2,3. Is there any way I can specify beginning and end in grep?

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  • Doubt regarding usage of array as a pointer in C

    - by Som
    For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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  • Dynamic memory allocation with default values

    - by viswanathan
    class A { private: int m_nValue; public: A() { m_nValue = 0; } A(int nValue) { m_nValue = nValue); ~A() {} } Now in main if i call A a(2);// 2 will be assigned for m_nValue of object A. Now how do we do this if i want to define an array of objects. Also how do we do this if i dynamically create objects using operator new like A *pA; pA = new A[5];// while creating the object i want the parameterised constructor to be //called I hope the question is clear. Do let me know if more explanation is needed

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  • name of class that manipulates the entities

    - by cyberguest
    hi, i have a general question regarding naming convention. if I separate the data and operations into two separate classes. one has the data elements (entity), the other class manipulates the entity class. what do we usually call that class that manipulates the entity class? (the entity I am referring to has nothing to do with any kind of entity framework) manager? controller? operator? manipulator? thanks in advance

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  • read integers from a file into a vector in C++

    - by user2922063
    I am trying to read an unknown number of double values stored on separate lines from a text file into a vector called rainfall. My code won't compile; I am getting the error no match for 'operator>>' in 'inputFile >> rainfall' for the while loop line. I understand how to read in from a file into an array, but we are required to use vectors for this project and I'm not getting it. I appreciate any tips you can give on my partial code below. vector<double> rainfall; // a vector to hold rainfall data // open file ifstream inputFile("/home/shared/data4.txt"); // test file open if (inputFile) { int count = 0; // count number of items in the file // read the elements in the file into a vector while ( inputFile >> rainfall ) { rainfall.push_back(count); ++count; } // close the file

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  • question about copy constructor

    - by lego69
    I have this class: class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; }; and I have function which contains this row: A *pa1 = new A(a2); can somebody please explain what exactly is going on, when I call A(a2) compiler calls copy constructor or constructor, thanks in advance

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  • How to get it working in O(n)?

    - by evermean
    I came across an interview task/question that really got me thinking ... so here it goes: You have an array A[N] of N numbers. You have to compose an array Output[N] such that Output[i] will be equal to multiplication of all the elements of A[N] except A[i]. For example Output[0] will be multiplication of A[1] to A[N-1] and Output[1] will be multiplication of A[0] and from A[2] to A[N-1]. Solve it without division operator and in O(n). I really tried to come up with a solution but I always end up with a complexity of O(n^2). Perhaps the is anyone smarter than me who can tell me an algorithm that works in O(n) or at least give me a hint...

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  • What is your most useful C/C++ utility?

    - by maddizzyro
    It seems that every project has an "utility" module with various code snippets used throughout other files and which don't fit any particular pattern. What utility classes, functions, and macros do you find most useful in your C/C++ projects? Please keep the entries small (under 100 lines) and give only one example per post.

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  • can function return 0 as reference

    - by helloWorld
    I have this snippet of the code Account& Company::findAccount(int id){ for(list<Account>::const_iterator i = listOfAccounts.begin(); i != listOfAccounts.end(); ++i){ if(i->nID == id){ return *i; } } return 0; } Is this right way to return 0 if I didn't find appropriate account? cause I receive an error: no match for 'operator!' in '!((Company*)this)->Company::findAccount(id)' I use it this way: if(!(findAccount(id))){ throw "hey"; } thanks in advance

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  • A php namespace called default

    - by michael
    <?php namespace default gives me an unexpecected T_DEFAULT, is there any way of working around this? Can I escape the reserved word somehow? My system uses the name of the current module in my site for the namespace so it would be nice to be able to use any string as a namespace.

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  • casting a node to integer

    - by user1708762
    The code gives an error saying that "no operator matches these two operands" in the if comparison statement. I interpret,it should mean that "a node can't be converted/casted into an integer". But, the print statement prints an integer value for w[2] when used with %d format. Why is that happening? Isn't printf casting it? NODE *w=(NODE *)malloc(4*sizeof(NODE)); if(w[2]==0) printf("%d\n",w[2]); The structure of the node is- struct node{ int key; struct node *father; struct node *child[S]; int *ss; int current; };

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  • Can typeid() be used to pass a function?

    - by Kerb_z
    I tried this and got the output as: void Please explain the following Code: #include <cstdio> #include <typeinfo> using namespace std ; void foo() { } int main(void) { printf("%s", typeid(foo()).name());// Please notice this line, is it same as typeid( ).name() ? return 0; } AFAIK: The typeid operator allows the type of an object to be determined at run time. So, does this sample code tell us that a function that returns void is of *type void*. I mean a function is a method and has no type. Correct?

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  • mySQL : using BETWEEN in table ?

    - by Meko
    I have a table that includes somestudent group name ,lesson time,day names like Schedule. I am using C# whit MYSql and I want to find which lesson is when user press button from table. I can find it like entering exact value like in table 08:30 or 10:25 , it finds. But I want to make that getting system time and checking that is it between 08:30 and 10:25 or 10:25 and 12:30 . Then I can sythat it is first lesson or it is second lesson . I have also table includes Table_Time column has 5 record like 08:20 , 10:25 , 12:20 so on. Could I use like : select Lesson_Time from mydb.clock where Lesson_Time between (current time)-30 AND (current time)+30 Or can I use between operator between two columns ? Like creating Lesson_Time_Start and Lesson_Time_End and compairing current time like Lesson_Start_Time

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  • Struts2 linking actions

    - by SonOfTheEARTh
    I am working on the Login module of my Struts2 app. I have created the Login Page, and a home Page(which is rendered by Login.action). Now i want to add another feature, forgot password which after performing its business must call the Login.action so that the user need not have to Login explicitly. what should i code and where so that as soon as the ForgotPassword.action finishes its work it passes control to Login.action.

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  • Do the changes to cpumask using sched_setaffinity() take place immediately

    - by Sukanto
    I am writing a linux kernel module that needs to pin two threads on two different cpus. I am planning to use sched_setaffinity() after exporting it in the kernel. Is there any other exported function for the same ? Also, if I set only 1 CPU in the cpumask, will the thread be moved to that cpu with immediate effect ? If not, how do I enforce the same ? Will it help to call schedule() just after sched_setaffinity() ?

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  • Performing an operation based on values within an array

    - by James W.
    I'm trying to figure out how to do operations based on values in an array. The values are taken from a string and inserted into the array e.g num = TextBox.Text.Split(' '); results = Convert.ToDouble(num[0]); for (int i = 0; i < num.Length - 1; i++) { if (num[i] == "+") { results += Convert.ToDouble(num[i++]); } ... } So based on this, let's say the TextBox string value was "1 + 2". So the array would be: ------------- | 1 | + | 2 | ------------- 0 1 2 (indexes) The part I'm having trouble with is Convert.ToDouble(num[i++]).. I've tried num[1] + 1, num[i + 1], etc I'm trying to figure out how to get it to perform the operation based on the first value and the value in the index after the operator. Which is the correct way to do something like this?

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