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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 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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  • 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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  • Redirect to prevent dup submission...but then you loose existing data

    - by coffeeaddict
    Here's the scenario User is on your checkout.aspx page Somewhere in the process, when clicking the pay button, you redirect the user to an intermediate page (before the confirmation page) to do some other logic. That intermediate page performs whatever logic based on a querystring flag you sent with the redirect from the checkout page This intermediate page also serves as an error page. So if any logic in the intermediatePage.aspx.cs fails I'm setting a message to be displayed on this page to the user If I refresh, that querystring value is still in the url..hence when it hits my Page_Load again, then the server-side logic is called & run again and I don't want this to happen The avoid this behavior/problem, the logical next step is to do a redirect back to the same page if they refresh (not sure how you'd catch that) to get rid of that querystring But when you redirect back to the same page your error message is gone, lost in the redirect therefore you end up showing them the same page but all values for the error message are now gone I do not want to solve this with Javascript either. I am not sure the best way to handle this.

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  • Joining two select queries and ordering results

    - by user1
    Basically I'm just unsure as to why this query is failing to execute: (SELECT replies.reply_post, replies.reply_content, replies.reply_date AS d, members.username FROM (replies) AS a INNER JOIN members ON replies.reply_by = members.id) UNION (SELECT posts.post_id, posts.post_title, posts.post_date AS d, members.username FROM (posts) as b WHERE posts.post_set = 0 INNER JOIN members ON posts.post_by = members.id) ORDER BY d DESC LIMIT 5 I'm getting this error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'a INNER JOIN members ON replies.re' at line 2 All I'm trying to do is select the 5 most recent rows (dates) from these two tables. I've tried Join, union etc and I've seen numerous queries where people have put another query after the FROM statement and that just makes no logical sense to me as to how that works? Am I safe to say that you can join the same table from two different but joined queries? Or am I taking completely the wrong approach, because frankly I can't seem see how this query is failing despite reading the error message. (The two queries on there own work fine)

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  • How to represent datetime of different time zomes in C#

    - by Mohoch
    I have a .NET WebService (written in C#), that is supposed to serve people around the world. With each request I get the user's datetime in his own time zone with the format : yyyy/MM/dd HH:mm ZZZZ. I have to convert the string to something representing the original date and time and specifying the time zone in GMT. I have to make some logical calculations and keep it in the database. The regular DateTime doe's not support this. it does not have a property specifying the time zone. When I try to convert my string into DateTime - it simply converts it to my local time. I do not want to keep my time in UTC, because I have some logic that has to run per user by his own time. Does anyone know a C# class that handles this?

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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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  • Aborted core dumped C++

    - by avd
    I have a large C++ function which uses OpenCV library and running on Windows with cygwin g++ compiler. At the end it gives Aborted(core dumped) but the function runs completely before that. I have also tried to put the print statement in the end of the function. That also gets printed. So I think there is no logical bug in code which will generate the fault. Please explain. I am also using assert statements.But the aborted error is not due to assert statement. It does not say that assertion failed. It comes at end only without any message. Also the file is a part of a large project so I cannot post the code also.

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  • Fulltext search not returning expected results

    - by Puneet
    I am experimenting with SQL Server full text search. I have a simple Categories table with Id as the primary key: CREATE TABLE [dbo].[Category]( [Id] [int] IDENTITY(1,1) NOT NULL, [CategoryName] [varchar](100) NOT NULL, ) My Query is: SELECT * FROM FREETEXTTABLE (Category, CategoryName, 'music') AS F INNER JOIN Category C ON F.[Key] = C.Id ORDER BY F.Rank DESC This returns me several records with the word music in them, but it does NOT return any record with word ‘musical’. Although, it can be said that the string being searched is not very big and using the LIKE operator will resolve it. I would like to use fulltext search because this simple example is going to be extended to include other tables and fileds.

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  • Retrieving a single Guid in CRM 4.0

    - by user1746560
    I'm new to CRM (version 4.0) and i'm trying to return a 'yearid' guide based on a given year (which is also stored in the entity).So far i've got: public static Guid GetYearID(string yearName) { ICrmService service = CrmServiceFactory.GetCrmService(); // Create the query object. QueryExpression query = new QueryExpression("year"); ColumnSet columns = new ColumnSet(); columns.AddColumn("yearid"); query.ColumnSet = columns; FilterExpression filter = new FilterExpression(); filter.FilterOperator = LogicalOperator.And; filter.AddCondition(new ConditionExpression { AttributeName = "yearName", Operator = ConditionOperator.Equal, Values = new object[] { yearName} }); query.Criteria = filter; } But my questions are: A) What code do in addition to this to actually store the Guid? B) Is using a QueryExpression the most efficient way to do this?

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  • RegularExpressionValidator always fails, but ValidationExpression works in testing

    - by Jerph
    I found the answer to this, but it's a bit of a gotcha so I wanted to share it here. I have a regular expression that validates passwords. They should be 7 to 60 characters with at least one numeric and one alpha character. Pretty standard. I used positive lookaheads (the (?= operator) to implement it: (?=^.{7,60}$)(?=.*[0-9].*)(?=.*[a-zA-Z].*) I checked this expression in my unit tests using Regex.IsMatch(), and it worked fine. However, when I use it in a RegularExpressionValidator, it always fails. Why?

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  • Friendness and derived class

    - by ereOn
    Hi, Let's say I have the following class hierarchy: class Base { protected: virtual void foo() = 0; friend class Other; }; class Derived : public Base { protected: void foo() { /* Some implementation */ }; }; class Other { public: void bar() { Derived* a = new Derived(); a->foo(); // Compiler error: foo() is protected within this context }; }; I guess I could change it too a->Base::foo() but since foo() is pure virtual in the Base class, the call will result in calling Derived::foo() anyway. However, the compiler seems to refuse a->foo(). I guess it is logical, but I can't really understand why. Am I missing something ? Can't (shouldn't) it handle this special case ? Thank you.

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  • I serialized a C++ object, how to allocate memory for it without knowing what type it is?

    - by Neo_b
    Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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  • How to declare a pointer to a variable as a parameter of a function in C++?

    - by Keand64
    I have a function that takes a pointer to a D3DXVECTOR3, but I have no reason to declare this beforehand. The most logical solution to me was using new: Function( //other parameters, new D3DXVECTOR3(x, y, 0)); but I don't know how I would go about deleting it, beign intitialized in a function. My next thought was to use the & operator, like so: Function( //other parameters, &D3DVECTOR3(x, y, 0)); but I don't know if this is a valid way to go about doing this. (It doesn't get an error, but neither does int *x; x = 50;). So should I use new, &, or some other technique I'm overlooking?

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  • deleting dynamically allocated object that contains vector in C++ STL

    - by kobac
    I have a class class ChartLine{ protected: vector<Point> line; // points connecting the line CString name; //line name for legend CPen pen; //color, size and style properties of the line }; where Point is a structure struct Point{ CString x; double y; }; In main() I dynamically allocate objects of type ChartLine with new operator. If I use delete afterwards, will default destructor ~ChartLine() properly dealocate (or clear) member ChartLine::line(which is vector btw) or I would have to clear that vector in ~ChartLine() manually? Thanks in advance. Cheers.

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  • Using template specialization in C++

    - by user550413
    How can I write a function using template specialization that has 2 different input types and an output type: template <class input1, class input2, class output> and return the sum of the 2 numbers (integers/doubles). However, if I get 2 integers I want to return an integer type but for any other combinations of integer and double I'll always return double. I am trying to do that without using directly the '+' operator but having the next functions instead: double add_double_double(double a, double b) {return (a+b);} double add_int_double(int a, double b) {return ((double)(a)+b);} int add_int_int(int a, int b) {return (a+b);}

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  • What types of conditions can be used for conditional compilation in C++?

    - by user1002288
    This is an exam question for C++: Which of the following statements accurately describe the condition that can be used for conditional compilation in C++? A. The condition can depend on the value of environment variables. B. The condition can depend on the value of any const variables. C. The condition can depend on the value of program variables. D. The condition can use the sizeof() operator to make decision about compiler-dependent operations based on the size of standard data type. E. The condition must evaluate to either a 0 or 1 during preprocessing. I think the answer is E. Is this correct?

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  • Finding the specific type held in an ArrayList<Object> (ie. Object = String, etc.)

    - by Christopher Griffith
    Say I have an ArrayList that I have cast to an ArrayList of objects. I know that all the objects that were in the ArrayList I cast were of the same type, but not what the type was. Now, if the ArrayList is not empty, I could take one of the objects in it and use the instanceof operator to learn what the actual type is. But what of the case where the ArrayList is empty? How do I determine what type Object actually is then? Is it possible?

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  • How to get total number of potential results in Lucene

    - by Slace
    I'm using lucene on a site of mine and I want to show the total result count from a query, for example: Showing results x to y of z But I can't find any method which will return me the total number of potential results. I can only seem to find methods which you have to specify the number of results you want, and since I only want 10 per page it seems logical to pass in 10 as the number of results. Or am I doing this wrong, should I be passing in say 1000 and then just taking the 10 in the range that I require?

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  • Postfix evaluation in C

    - by Andrewziac
    I’m taking a course in C and we have to make a program for the classic Postfix evaluation problem. Now, I’ve already completed this problem in java, so I know that we have to use a stack to push the numbers into, then pop them when we get an operator, I think I’m fine with all of that stuff. The problem I have been having is scanning the postfix expression in C. In java it was easier because you could use charAt and you could use the parseInt command. However, I’m not aware of any similar commands in C. So could anyone explain a method to read each value from a string in the form: 4 9 * 0 - = Where the equals is the signal of the end of the input. Any help would be greatly appreciated and thank you in advance :)

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  • How to insert into std::map.

    - by Knowing me knowing you
    In code below: map<string,vector<int>> create(ifstream& in, const vector<string>& vec) { /*holds string and line numbers into which each string appears*/ typedef map<string,vector<int>> myMap; typedef vector<string>::const_iterator const_iter; myMap result; string tmp; unsigned int lineCounter = 0; while(std::getline(in,tmp)) { const_iter beg = vec.begin(); const_iter end = vec.end(); while (beg < end) { if ( tmp.find(*beg) != string::npos) { result[*beg].push_back(lineCounter);//THIS IS THE LINE I'M ASKING FOR } ++beg; } ++lineCounter; } return result; } How should I do it (check line commented in code) if I want to use insert method of map instead of using operator[]? Thank you.

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  • InApp subscriptions - trasferability

    - by meap
    Apple has rejected one of our apps, where the user can purchase content through subscriptions (InApp product type is subscription). The problem is that we need to, also because of Apple requiring it, these subscriptions to be transferable between devices. The logical and also the most secure solution would be to link it to a user account, that the user will have to create. But this was the reason why apple rejected this app. They have told us that for purchasing of subscriptions a registration can not be required, can be only optional. So the question is how to solve this if there is no other nice solution that would make sense, be secure and still comfortable for the user?

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  • Testing what a String token holds

    - by Yiwei Gao
    I am making a calculator and part of this program takes in user String input and tokenizes it (using my own implementation of a Tokenizer class). So now I have a bunch of Token objects and I would like to test each one of them to see if they hold numbers or operators. Is there a way to test to see if they hold operators (ie. +, -, *, /, =, (, ), etc.) without using if (token.equals("+") || token.equals("-") || ... and so on, for each operator? These Token objects are all of type String.

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  • C pointer question, dereferencing crash

    - by skynorth
    Why do this work? int *var; while(scanf("%d", &var) && *var != 0) printf("%d \n", var); While this does not? int *var; while(scanf("%d", &var) && var != 0) printf("%d \n", var); Doesn't * (dereference operator) give you the value pointed by the pointer? So why does *var != 0 crash the program, while var != 0 does not?

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  • Quickest way to compute the number of shared elements between two vectors

    - by shn
    Suppose I have two vectors of the same size vector< pair<float, NodeDataID> > v1, v2; I want to compute how many elements from both v1 and v2 have the same NodeDataID. For example if v1 = {<3.7, 22>, <2.22, 64>, <1.9, 29>, <0.8, 7>}, and v2 = {<1.66, 7>, <0.03, 9>, <5.65, 64>, <4.9, 11>}, then I want to return 2 because there are two elements from v1 and v2 that share the same NodeDataIDs: 7 and 64. What is the quickest way to do that in C++ ? Just for information, note that the type NodeDataIDs is defined as I use boost as: typedef adjacency_list<setS, setS, undirectedS, NodeData, EdgeData> myGraph; typedef myGraph::vertex_descriptor NodeDataID; But it is not important since we can compare two NodeDataID using the operator == (that is, possible to do v1[i].second == v2[j].second)

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