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  • Another problem with decltype

    - by There is nothing we can do
    template<class IntT, IntT low = IntT(), IntT high = IntT()> struct X { static_assert(std::is_same<decltype(low),decltype(high)>::value,"Different types not allowed");//this should give error if types are different decltype(low) a; decltype(high) b; X():a(decltype(a)()),b(decltype(b)())//WHY THIS DOES NOT COMPILE? { cout << typeid(a).name() << '\n'; cout << typeid(b).name() << '\n'; } }; int _tmain(int argc, _TCHAR* argv[]) { X<char,1,'a'> x;//this according to static_assert shouldn't compile but it does return 0; } Using VS2010. Please see 3 comments in code above.

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  • What are the advantages of squashing assignment and error checking in one line?

    - by avakar
    This question is inspired by this question, which features the following code snippet. int s; if((s = foo()) == ERROR) print_error(); I find this style hard to read and prone to error (as the original question demonstrates -- it was prompted by missing parentheses around the assignment). I would instead write the following, which is actually shorter in terms of characters. int s = foo(); if(s == ERROR) print_error(); This is not the first time I've seen this idiom though, and I'm guessing there are reasons (perhaps historical) for it being so often used. What are those reasons?

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  • Accessing primitive properties from objects stored in a NSDictionary

    - by ChrisS
    Apologies if this is a basic question, I am just starting with Objective-C and trying to wrap things around in my head! I have a simple class of the form: @interface Whatever : NSObject { int somePrimitive; SomeObject* someObject; } @property (nonatomic) int somePrimitive; @property (nonatomic, retain) SomeObject* someObject; The class is more involved that this, but this illustrates the purpose. When I store instances of this class in a NSMutableDictionary: Whatever *whatever = [[Whatever alloc] init]; whatever.somePrimitive = 1; whatever.someObject = ...; [myDictionary setObject:whatever forKey:@"someKey"]; and then try to retrieve the object later: Whatever *result = [myDictionary valueForKey:@"someKey"]; then, result.someObject is ok to reference but, result.somePrimitive crashes. Does the NSDictionary not copy over the primitives of the object? Is the rule that the object stored in a dictionary should only contain objects?

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  • Refactoring a nested loop

    - by user3517441
    I have the following code which I use a lot of times in the class. for (int i = 0; i < someList.size(); i++) { for (int j = 0; j < someList.size(); j++) { if (i != j) { someList.get(i).sendMessageTo(someList.get(j))); //variable action } } } The purpose of the loop is to make each element in the List to send a message (or perform another action) to every element in the list except itself. Is there any way I can create a helper method so I don't have to repeat the loop code. I want to be able to state the variable action and call the helper method. Thanks.

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  • Writing loops with i++ or ++i [duplicate]

    - by Nonesuch
    This question already has an answer here: Why use ++i instead of i++ in cases where the value is not used anywhere else in the statement? 6 answers format of for loops 31 answers I have a question about writing loops. I always begin with (int i=0; i<10; i++) But I see many experts begin with (int i=0; i<10; ++i) Is there there any real difference, or they are same? Of course, I know the difference between pre-increment and post-increment. I mean which one I should use when writing the loop? or it depends. Thanks!

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  • Java Collections.Rotate with an array doesn't work

    - by steve_72
    I have the following java code: import java.util.Arrays; import java.util.Collections; public class Test { public static void main(String[] args) { int[] test = {1,2,3,4,5}; Collections.rotate(Arrays.asList(test), -1); for(int i = 0; i < test.length; i++) { System.out.println(test[i]); } } } I want the array to be rotated, but the output I get is 1 2 3 4 5 Why is this? And is there an alternative solution?

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  • error message fix

    - by user1722654
    for (int i = 0; i < dataGridView1.Rows.Count; i++) { //bool sleected = false; if (dataGridView1.Rows[i].Cells[3].Value != null) { selected.Add(i); } } //string donew = ""; // line off error textBox1.Text = ((String)dataGridView1.Rows[1].Cells[2].Value); /* for (int i = 0; i < selected.Count; i++) { textAdded.Add((String)dataGridView1.Rows[0].Cells[2].Value); // donew += (String)dataGridView1.Rows[selected[i]].Cells[2].Value; }*/ I keep getting the error Unable to cast object of type 'System.Double' to type 'System.String' What can I do to overcome this?

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  • What is the complexity of this c function

    - by Bunny Rabbit
    what is the complexity of the following c Function ? double foo (int n) { int i; double sum; if (n==0) return 1.0; else { sum = 0.0; for (i =0; i<n; i++) sum +=foo(i); return sum; } } Please don't just post the complexity can you help me in understanding how to go about it . EDIT: It was an objective question asked in an exam and the Options provided were 1.O(1) 2.O(n) 3.O(n!) 4.O(n^n)

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  • C++ how to store integer into a binary file??

    - by blaxc
    i gt a struct with 2 integer, i want to store them in a binary file and read it again... here is my code... struct pw { int a; int b; }; void main(){ pw* p = new pw(); pw* q = new pw(); std::ofstream fout(ADMIN_FILE, ios_base::out | ios_base::binary | ios_base::trunc); std::ifstream fin(ADMIN_FILE, ios_base::in | ios_base::binary); p->a=123; p->b=321; fout.write((const char*)p, sizeof(pw)); fin.write((char*)q, sizeof(pw)); fin.close(); cout<< q->a << endl;} my output is 0. anyone can tell me what is the problem?

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  • Getting input in system() function (Mac)

    - by Alex
    #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

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  • C++ destructor issue with std::vector of class objects

    - by Nigel
    I am confused about how to use destructors when I have a std::vector of my class. So if I create a simple class as follows: class Test { private: int *big; public: Test () { big = new int[10000]; } ~Test () { delete [] big; } }; Then in my main function I do the following: Test tObj = Test(); vector<Test> tVec; tVec.push_back(tObj); I get a runtime crash in the destructor of Test when I go out of scope. Why is this and how can I safely free my memory?

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  • i have done code so please help

    - by davit-datuashvili
    public class bitap{ public static void main(String[]args){ String text="tbillisi"; String pattern="tbilxiri"; int k=2; int m=pattern.length(); long pattern_mask[]=new long[Character.MAX_VALUE+1]; String result=""; boolean[]R=new boolean[m+1]; long i,d; for (i=0;i<=k;i++){ R[i]=~1; } for (i=0;i if (0==(R[k]& (1< System.out.println(result); } } http://en.wikipedia.org/wiki/Bitap_algorithm from this site

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  • How can I optimize this code?

    - by loop0
    Hi, I'm developing a logger daemon to squid to grab the logs on a mongodb database. But I'm experiencing too much cpu utilization. How can I optimize this code? from sys import stdin from pymongo import Connection connection = Connection() db = connection.squid logs = db.logs buffer = [] a = 'timestamp' b = 'resp_time' c = 'src_ip' d = 'cache_status' e = 'reply_size' f = 'req_method' g = 'req_url' h = 'username' i = 'dst_ip' j = 'mime_type' L = 'L' while True: l = stdin.readline() if l[0] == L: l = l[1:].split() buffer.append({ a: float(l[0]), b: int(l[1]), c: l[2], d: l[3], e: int(l[4]), f: l[5], g: l[6], h: l[7], i: l[8], j: l[9] } ) if len(buffer) == 1000: logs.insert(buffer) buffer = [] if not l: break connection.disconnect()

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  • Entity Framework: Attached Entities not Saving

    - by blog
    Hello: I can't figure out why calling SaveChanges() on the following code results in no changes to the objects I attached: // delete existing user roles before re-attaching if (accountUser.AccountRoles.Count > 0) { foreach (AccountRole role in accountUser.AccountRoles.ToList()) { accountUser.AccountRoles.Remove(role); } } // get roles to add List<int> roleIDs = new List<int>(); foreach (UserRole r in this.AccountRoles) { roleIDs.Add(r.RoleID); } var roleEntities = from roles in db.AccountRoles where roleIDs.Contains(roles.id) select roles; accountUser.AccountRoles.Attach(roleEntities); db.SaveChanges(); In the debugger, I see that the correct roleEntities are being loaded, and that they are valid objects. However, if I use SQL Profiler I see no UPDATE or INSERT queries coming in, and as a result none of my attached objects are being saved.

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  • Java: Best approach to have a long list of variables needed all the time without consuming memory?

    - by evilReiko
    I wrote an abstract class to contain all rules of the application because I need them almost everywhere in my application. So most of what it contains is static final variables, something like this: public abstract class appRules { public static final boolean IS_DEV = true; public static final String CLOCK_SHORT_TIME_FORMAT = "something"; public static final String CLOCK_SHORT_DATE_FORMAT = "something else"; public static final String CLOCK_FULL_FORMAT = "other thing"; public static final int USERNAME_MIN = 5; public static final int USERNAME_MAX = 16; // etc. } The class is big and contains LOTS of such variables. My Question: Isn't setting static variables means these variables are floating in memory all the time? Do you suggest insteading of having an abstract class, I have a instantiable class with non-static variables (just public final), so I instantiate the class and use the variables only when I need them. Or is what am I doing is completely wrong approach and you suggest something else?

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  • Why does this static factory method involving implied generic types, work?

    - by Cheeso
    Consider public class Tuple<T1, T2> { public Tuple(T1 v1, T2 v2) { V1 = v1; V2 = v2; } public T1 V1 { get; set; } public T2 V2 { get; set; } } public static class Tuple { // MAGIC!! public static Tuple<T1, T2> New<T1, T2>(T1 v1, T2 v2) { return new Tuple<T1, T2>(v1, v2); } } Why does the part labeled "MAGIC" in the above work? It allows syntax like Tuple.New(1, "2") instead of new Tuple<int, string>(1, "2"), but ... how and why? Why do I not need Tuple.New<int,string>(1, "2") ??

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  • When should we use * and & and . and -> ?

    - by uzay95
    Why we are using * character when we are creating button but we aren't adding it to app instance? #include <QApplication> #include <QPushButton> int main(int argc,char *argv[]) { QApplication app(argc,argv); QPushButton *button = new QPushButton("Button Text"); QObject::connect(button,SIGNAL(clicked()),&app,SLOT(quit())); button->show(); return app.exec(); } When should we use * and & and . and - ?

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  • TSQL Prefixing String Literal on Insert - Any Value to This, or Redundant?

    - by SethO
    I just inherited a project that has code similar to the following (rather simple) example: DECLARE @Demo TABLE ( Quantity INT, Symbol NVARCHAR(10) ) INSERT INTO @Demo (Quantity, Symbol) SELECT 127, N'IBM' My interest is with the N before the string literal. I understand that the prefix N is to specify encoding (in this case, Unicode). But since the select is just for inserting into a field that is clearly already Unicode, wouldn't this value be automatically upcast? I've run the code without the N and it appears to work, but am I missing something that the previous programmer intended? Or was the N an oversight on his/her part? I expect behavior similar to when I pass an int to a decimal field (auto-upcast). Can I get rid of those Ns?

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  • What would a compress method do in a hash table?

    - by Bradley Oesch
    For an assignment I have to write the code for a generic Hash Table. In an example Put method, there are two lines: int hash = key.hashCode(); // get the hashcode of the key int index = compress(hash); // compress it to an index I was of the understanding that the hashCode method used the key to return an index, and you would place the key/value pair in the array at that index. But here we "compress" the hash code to get the index. What does this method do? How does it "compress" the hash code? Is it necessary and/or preferred?

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  • Determine if FieldInfo is compiler generated backingfield

    - by Steffen
    The title pretty much says it all, how do I know if I'm getting a compiler generated backingfield for a {get; set;} property ? I'm running this code to get my FieldInfos: Class MyType { private int foo; public int bar {get; private set; } } Type type = TypeOf(MyType); foreach (FieldInfo fi in type.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.NonPublic)) { // Gets both foo and bar, however bar is called <bar>k__backingfield. } so the question is, can I somehow detect that the FieldInfo is a backingfield, without relying on checking its name ? (Which is pretty undocumented, and could be broken in next version of the framework)

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  • How to convert string to integer?

    - by user1260584
    So I'm having a hard time with my situation and need some advice. I'm trying to convert my two Strings that I have into integers, so that I can use them in math equations. Here is what I tried, however it brings me an error in the app. ' equals.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { // TODO Auto-generated method stub num1 = edit.getText().toString(); num2 = edit.getText().toString(); int first = Integer.parseInt(num1); int second = Integer.parseInt(num2); edit.setText(first + second); } }); Is there something that I am doing wrong? Thank you for any help. EDIT: Yes this is Java. num1 and num2 are strings that I have previously named. What do you mean by trim?

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  • How to set a value from another class

    - by Ram
    Its said that property should not be "Set" only and it should be "Get" as well. What should i do if I need to set value to a variable from some other class? The will keep changing so I cannot pass it through constructor. Shall I create a function for this as shown below? class A { public void SetValue() { b = new B(); b.SetTest(10); } } class B { int test; public void SetTest(int value) { test = value; } } What are the other alternatives?

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  • In C++, I want to implement a ring iterator for a deque that contains a personally defined class.

    - by George
    I have a function of a "Table" class that should add a player to the table. I decided that if the seat is taken, the function should try and go through all the seats and add the player to the next available seat. How do I implement this in my addPlayer function? int Table::addPlayer(Player player, int position) { deque<Player>::iterator it; if(playerList[position] != "(empty seat)") { //What goes here? } playerList.put(player,it); cout >> "Player " >> player.toString >> " sits at position " >> position >> endl; }

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  • C++ Function Calling Itself

    - by Ben
    Suppose I wish to have a function that fills an array either in pattern x,y,x,y,x,ywhere x and y are variables defined by some algorithm and x,y,z,x,y,z where x, y and z are variables defined by the same algorithm. This should continue for all number of variables. Is this a viable way to implement it. int recurse_n(int n) { while(n > 0) { --n; recurse_n(n); n = 0; // Use algorithm here } }

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  • "An access violation (Segmentation Fault) raised in your program."

    - by Mark
    My C++ program compiles and works up until I call this function from main(): int uword(){fstream infile("numbers.txt"); fstream exfile("wordlist.txt"); string numb[numoflines]; string lines[numoflines]; number = 1; line = 1; for(int i=0;!infile.eof();++i) { getline (infile,number); numb[i] = number; getline (exfile,line); lines[i] = line; } infile.close(); exfile.close(); string yourword; Something here causes it to crash, in the debug it pops up with "An access violation (Segmentation Fault) raised in your program."

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