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• Storing expression template functors

  - by UncaughtException

  Hello guys, at the moment I'm really interested in expression templates and want to code a library for writing and differentiating mathematical functions with a lambda-style syntax. At the moment, I'm able to write (_x * _x)(2); and get the correct result 4. But I would really like to do something like MathFunction f = _x * _x; f(2);, but I don't have any ideas on how to cope with the recursive expression templates on the right side. Is it possible to achieve this without using the 'auto'-Keyword instead of MathFunction or having to make the operator() virtual? Thanks for your help!

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• Does std::multiset guarantee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• How to retrieve large data from oracle database using vbscript

  - by allenzzzxd

  Hi guys, I'm now working on vbscript to do some test. Actuelly, I want to retrieve a large amount of data from an oracle database, so I write the code like this: sql = "Select * from CORE_DB where MC = '" & mstr & "' " Set myrs = db_execute_query(curConnection, sql) Then I count the rows in myrs,there are 248 rows. So then I do a For loop to retrieve some fields of each row. For k = 0 To db_get_rows_count(myrs) But then I found that the content of the row k when k 133 was always equal to k = 133. So this makes an error. As I think, there may be a limit size of mrys ? Could anyone light me about this? Thanks a lot in advance

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• Is there a shorthand way to denullify a string in C#?

  - by Moose Factory

  Is there a shorthand way to denullify a string in C#? It would be the equivalent of (if 'x' is a string): string y = x == null ? "" : x; I guess I'm hoping there's some operator that would work something like: string y = #x; Wishful thinking, huh? The closest I've got so far is an extension method on the string class: public static string ToNotNull(this string value) { return value == null ? "" : value; } which allows me to do: string y = x.ToNotNull(); Any improvements on that, anyone?

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• Why isn't Perl's File::GlobMapper exporting globmap?

  - by justintime

  The following is pretty well copied from the documentation. use File::GlobMapper qw( globmap ); for my $pair (globmap '<*.tar.gz>' => '<#1.tgz>' ) { } And it gives String found where operator expected at globmapper_test1.pl line 4, near "globmap '<*.tar.gz>'" (Do you need to predeclare globmap?) (Using ActivePerl 5.10.0 on Windows) Side questions - if GlobMapper only exports one function, why is it set so you have to export it explicitly?

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• Silverlight Question: How can I find the DataTemplate corresponding to an item in a ListBox

  - by morpheus

  I have two classes A & B, and a listbox. I assign listBox.ItemsSource equal to a collection of objects of type A. The listbox items are visualized using silverlight data templating, see http://msdn.microsoft.com/en-us/library/system.windows.datatemplate.aspx and http://www.codeproject.com/KB/WPF/UserControlAsDataTemplate.aspx for example. The listbox.ItemTemplate is a DataTemplate that uses class B to visualize the listbox items. Now, in my code-behind, inside any method of class B, if I do this.DataContext, it points to an object of type A. Thus, given an object of type B, I can find the corresponding object of type A. So far so good. My question is, given an object of type A, how can I navigate to the corresponding object of type B? Is this even possible in SL?

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• help implementing All Nearest Smaller Values algorithm

  - by davit-datuashvili

  http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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• Why does a Linq Cast<T> operation fail when I have an implicit cast defined?

  - by Ryan Versaw

  I've created two classes, with one of them having an implicit cast between them: public class Class1 { public int Test1; } public class Class2 { public int Test2; public static implicit operator Class1(Class2 item) { return new Class1{Test1 = item.Test2}; } } When I create a new list of one type and try to Cast<T> to the other, it fails with an InvalidCastException: List<Class2> items = new List<Class2>{new Class2{Test2 = 9}}; foreach (Class1 item in items.Cast<Class1>()) { Console.WriteLine(item.Test1); } This, however, works fine: foreach (Class1 item in items) { Console.WriteLine(item.Test1); } Why is the implicit cast not called when using Cast<T>?

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• How to force a deep copy when copying structs with arrays?

  - by Danvil

  If have a struct A { public double[] Data; public int X; } How can I force a deep copy when using operator= or adding instances of A to a container? The problem is for example: A a = new A(); var list = new List<A>(); list.Add(a); // does not make a deep copy of Data A b = a; // does not make a deep copy of Data Do I really have to implement my own DeepClone method and call it every time? This would be extremly error-prone ...

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• Using pipes inside a class in C++

  - by Paul

  I'm trying to use this tutorial to make plots with Gnuplot in C++. However I will be using the pipe to Gnuplot from within a class, but then I run into some problems: I've got a header file where I declare all variables etc. I need to declare the pipe-variable here too, but how do I do that? I've tried doing it straight away, but it doesn't work: Logger.h: class Logger { FILE pipe; } Logger.cpp: Logger::Logger() { //Constructor *pipe = popen("gnuplot -persist","w"); } Gives the error Logger.cpp:28: error: no match for ‘operator=’ in ‘*((Logger*)this)->Logger::pipe = popen(((const char*)"gnuplot -persist"), ((const char*)"w"))’ Suggestions?

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• How to get dataset to populate data into dbgrid in Delphi 6?

  - by Chris J

  I have created a DBGrid in Delphi 6 and tied it to a DataSource contained in a DataModule. The Dataset for that source in also located in the same module. In the OnShow event for the form, I activate the dataset and set a label equal to the rowcount for the dataset. This shows several hundred rows but nothing shows in the dbgrid. If I activate the dataset in the IDE, the grid populates with the expected data. Does anyone have any idea why this behaviour would change between the IDE and normal runtime? We are also using SDAC connection components. All 3rd party component choices are not mine to change. I can elaborate as necessary for clarification, but I mainly need troubleshooting ideas to start at.

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• C++ Word-Number to int

  - by Andrew

  I'm developing a program that makes basic calculations using words instead of numbers. E.g. five + two would output seven. The program becomes more complex, taking input such as two_hundred_one + five_thousand_six (201 + 5006) Through operator overloading methods, I split each number and assign it to it's own array index. two would be [0], hundred is [1], and one is [2]. Then the array recycles for 5006. My problem is, to perform the actual calculation, I need to convert the words stored in the array to actual integers. I have const string arrays such as this as a library of the words: const string units[] = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; const string teens[] = { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" }; const string tens[] = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" }; If my 'token' array has stored in it two hundred one in index 0, 1, and 2, I'm not sure what the best way to convert these to ints would involve.

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• Python 3: Most efficient way to create a [func(i) for i in range(N)] list comprehension

  - by mejiwa

  Say I have a function func(i) that creates an object for an integer i, and N is some nonnegative integer. Then what's the fastest way to create a list (not a range) equal to this list mylist = [func(i) for i in range(N)] without resorting to advanced methods like creating a function in C? My main concern with the above list comprehension is that I'm not sure if python knows beforehand the length of range(N) to preallocate mylist, and therefore has to incrementally reallocate the list. Is that the case or is python clever enough to allocate mylist to length N first and then compute it's elements? If not, what's the best way to create mylist? Maybe this? mylist = [None]*N for i in range(N): mylist[i] = func(i)

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• Undefined / Uninitialized default values in a class

  - by Jir

  Let's suppose you have this class: class A { public: A () {} A (double val) : m_val(val) {} ~A () {} private: double m_val; }; Once I create an instance of A, how can I check if m_val has been initialized/defined? Put it in other words, is there a way to know if m_val has been initialized/defined or not? Something along the lines of the defined operator in Python, I suppose. (But correct me if I'm wrong.) I thought of modifying the class and the c-tors the following way: class A { public: A () : defined(false) {} A (double val) : m_val(val), defined(true) {} ~A () {} private: double m_val; bool defined; }; How do you rate this solution? Any suggestion? TIA, Chris

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• <= vs < when proving big-o notation

  - by user600197

  We just started learning big-o in class. I understand the general concept that f(x) is big-o of g(x) if there exists two constants c,k such that for all xk |f(x)|<=c|g(x)|. I had a question whether or not it is required that we include the <= to sign or whether it is just sufficient to put the < sign? For example: suppose f(x)=17x+11 and we are to prove that this is O(x^2). Then if we take c=28 and xk=1 we know that 17x+11<=28x^2. So since we know that x will always be greater than 1 this implies that 28x^2 will always be greater than 17x+11. So, do we really need to include the equal sign (<=) or is it okay if we just write (<)? Thanks in advance.

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• Using Where method in Linq 2 Entities with OR clause.

  - by Dani

  I want to use Where method in Linq 2 entities that will be equal to this userRepository.Users.Where(u=>u.RoleID == 1 || u=>u.RoldID == 2).Select(o => new SelectListItem { Text = o.Role.RoleName, Value = o.RoleID.ToString() }).ToList(); The problem of course is in Where(u=u.RoleID == 1 || u=u.RoldID == 2) The problem is that I don't know how to use WHERE method with OR inside the WHERE clause. any ideas (the code above will not compile of-course b/c of the lambda expression. userRepository.Users returns an list of Users entities. I guess that and can be done using concatenation of .Where().Where() but I need an OR.

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• Java: PriorityQueue returning incorrect ordering from custom comparator??

  - by Michael Simpson

  I've written a custom comparator to compare my node classes, but the java priority queue is not returning my items in the correct order. Here is my comparator: public int compare(Node n1, Node n2){ if (n1.getF() > n2.getF()){ return +1; } else if (n1.getF() < n2.getF()){ return -1; } else { // equal return 0; } } Where getF returns a double. However after inserting several Nodes into the priority queue, I print them out using: while(open.size() > 0) { Node t = (Node)(open.remove()); System.out.println(t.getF()); } Which results in: 6.830951894845301 6.830951894845301 6.0 6.0 5.242640687119285 7.4031242374328485 7.4031242374328485 8.071067811865476 Any ideas why this is so? Is my comparator wrong? Thanks. Mike

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• Java multidimensional array and scanner novice Q

  - by Max

  I'm new to Java and trying to in essence implement a grid with a character, and if the user inputs 'w' 'a' 's' or 'd' the character moves up/down/left/right within the plane. I created a multidimensional array sized 10x10 public static String[][] grid = new String[10][10]; And then just used a for loop to print "*"s in a 10x10 grid, except for grid[a][b] which is equal to character "A" i.e. my thing to be moved around. That seemed to work alright, then I needed to detect the 'wasd' input from the user so I set up a: Scanner in = new Scanner (System.in); while (in.hasNext()) And I had then: String s = in.next(); char ch = s.charAt(0); switch (ch) but I couldn't make this work, and it wasn't because I didn't complete the "switch" statement, I did, I just see it void copying and pasting the entire thing. I'm sure its incredibly easy slight thing I am missing, can you please point it out for me?

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• Neo4j+Gremlin : Trouble with T.gte and floating point node attributes

  - by letronje

  For a type of nodes in my graph, attribute values for an attribute(named 'some_count') is either missing or an integer or a float. I'm trying to write gremlin to filter these nodes based on minimum value for this attribute. I first verified that the values are indeed present by firing the following gremlin g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).some_count Next, I tried filtering by exact value and that works and show me the matching nodes or gives an empty array if there is no match g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).has('some_count', T.eq, 120000.0d) But the following query that uses the 'greater than or equal to' comparator doesn't work. g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).has('some_count', T.gte, 1.0d) this returns nil (I'm querying via ruby/rails using Neo4j AR Adapter ) Instead of returning an empty array for no match, it returns a nil, which tells me something could be wrong with the query itself. I'm running neo4j community server 1.8. Is there a way I can ask Neo4j to log errors/queries, to see what could be going wrong ?

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• Force an object to be allocated on the heap

  - by Warren Seine

  A C++ class I'm writing uses shared_from_this() to return a valid boost::shared_ptr<>. Besides, I don't want to manage memory for this kind of object. At the moment, I'm not restricting the way the user allocates the object, which causes an error if shared_from_this() is called on a stack-allocated object. I'd like to force the object to be allocated with new and managed by a smart pointer, no matter how the user declares it. I thought it could be done through a proxy or an overloaded new operator, but I can't find a proper way of doing that. Is there a common design pattern for such usage? If it's not possible, how can I test it at compile time?

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• How do I prevent a pair of XMLEvent[Reader|Writer] from splitting empty tags into start+end tags?

  - by java.is.for.desktop

  Hello, everyone! I have an understanding problem of how the following code works: XMLInputFactory xif = XMLInputFactory.newFactory(); XMLOutputFactory xof = XMLOutputFactory.newFactory(); XMLEventReader reader = xif.createXMLEventReader(/* ... */); XMLEventWriter writer = xof.createXMLEventWriter(/* ... */); writer.add(reader); The method writer.add([some reader]) reads all events from reader and writes them consequently. Sadly, following happens: The input <root><c/></root> gets transformed to <root><c><c/></root> I know, from XML point of view, these are equal trees, but not for a human ;) What can I do to get the same output? FYI: I need a XMLEvent[Reader|Writer] pair later to filter "XML events".

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• Glib::ustring and Japanese characters

  - by user294787

  Glib::ustring is supposed to work well with UTF8 but I have a problem when working with Japanese strings. If you compare those two strings, "???" and "???", using == operator or compare method, it will answer that those two strings are equals. I don't understand why. How Glib::ustring works ? The only way I found to get false to the comparison is to compare strings of different sizes. For example "?????" and "????". Very strange...

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• How Do I Update a Table From Another Table Only If the Result Count is 1?

  - by Russ Bradberry

  I have a table of 2 tables in a one to many relationship. I want to run an update script that will update the table with the FK of the related table only if there is one result (because if there is multiple then we need to decide which one to use, in another method) Here is what I have so far: UPDATE import_hourly_event_reports i SET i.banner_id = b.banner_id FROM banner b JOIN plan p ON b.plan_id = p.id WHERE b.campain_id = i.campaign_id AND b.size_id = i.size_id AND p.site_id = i.site_id HAVING COUNT(b.banner_id) = 1 As you can see, the HAVING clause doesn't quite work as I'd expect it. I only want to update the row in the import table with the id of the banner from the banner table if the count is equal to 1.

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• Is there a file diff tool that allows for exceptions?

  - by Kevin

  We currently use Beyond Compare 3.0 and I am quite pleased with it. However, it would be great if I could easily specify an exclusion for a specific one-time case. This is needed when I am doing a code review of some refactoring. For instance: Old code doSomething(ConstantsInterface.FOOBAR); New code: doSomething(BetterEnumeration.FOOBAR); In this case, I have hundreds of changes that I am reviewing that are essentially all the same exact change and I just want to see the exceptions. It would be great if I could easily specify an exception that indicates these two cases are equal. I know of a way to do it in the grammar, but it is tedious and cumbersome in the case where there are ten or so exceptions. Any other tips?

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