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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 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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  • Second query to SQLite (on iPhone) errors.

    - by Luke
    Hi all, On the iPhone, I am developing a class for a cart that connects directly to a database. To view the cart, all items can be pulled from the database, however, it seems that removing them doesn't work. It is surprising to me because the error occurs during connection to the database, except not the second time I connect even after the DB has been closed. #import "CartDB.h" #import "CartItem.h" @implementation CartDB @synthesize database, databasePath; - (NSMutableArray *) getAllItems { NSMutableArray *items = [[NSMutableArray alloc] init]; if([self openDatabase]) { const char *sqlStatement = "SELECT * FROM items;"; sqlite3_stmt *compiledStatement; if(sqlite3_prepare_v2(cartDatabase, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) { while(sqlite3_step(compiledStatement) == SQLITE_ROW) { int rowId = sqlite3_column_int(compiledStatement, 0); int productId = sqlite3_column_int(compiledStatement, 1); NSString *features = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)]; int quantity = sqlite3_column_int(compiledStatement, 3); CartItem *cartItem = [[CartItem alloc] initWithRowId:rowId productId:productId features:features quantity:quantity]; [items addObject:cartItem]; [cartItem release]; } } sqlite3_finalize(compiledStatement); } [self closeDatabase]; return items; } - (BOOL) removeCartItem:(CartItem *)item { sqlite3_stmt *deleteStatement; [self openDatabase]; const char *sql = "DELETE FROM items WHERE id = ?"; if(sqlite3_prepare_v2(cartDatabase, sql, -1, &deleteStatement, NULL) != SQLITE_OK) { return NO; } sqlite3_bind_int(deleteStatement, 1, item.rowId); if(SQLITE_DONE != sqlite3_step(deleteStatement)) { sqlite3_reset(deleteStatement); [self closeDatabase]; return NO; } else { sqlite3_reset(deleteStatement); [self closeDatabase]; return YES; } } - (BOOL) openDatabase { if(sqlite3_open([databasePath UTF8String], &cartDatabase) == SQLITE_OK) { return YES; } else { return NO; } } - (void) closeDatabase { sqlite3_close(cartDatabase); } The error occurs on the line where the connection is opened in openDatabase. Any ideas? Need to flush something? Something gets autoreleased? I really can't figure it out. --Edit-- The error that I receive is GDB: Program received signal "EXC_BAD_ACCESS". --Edit-- I ended up just connecting in the init and closing in the free methods, which might not be the proper way, but that's another question altogether so it's effectively persistent instead of connecting multiple times. Still would be nice to know what was up with this for future reference.

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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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  • Reading line by line from a file in C

    - by mh234
    What I am trying to do is print out the contents of a file line by line. I run the program in terminal by doing: ./test testText.txt. When I do this, random characters are printed out but not what is in the file. The text file is located in the same folder as the makefile. What's wrong? #include <stdio.h> FILE *fp; int main(int argc, char *argv[]) { char line[15]; fp = fopen(*argv, "r"); while((fgets(line, 15, fp)) != NULL) { printf(line); printf("\n"); } }

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  • C++: Throwing shared_ptr of derived and catching shared_ptr of base?

    - by hasvn
    Ok, I've been told this problem: Why can you throw a pointer to a derived class and catch a pointer to its base... but you can't do that with shared_ptrs? Example, this works: class Base {}; class Derived : public Base {}; int main() { try { throw new Derived() ; } catch( const Base2 * b ) { printf("Received a base" ) ; } return 0 ; } But this doesn't int main() { try { throw std::tr1::shared_ptr<Derived>( new Derived() ) ; } catch( const std::tr1::shared_ptr<Base> & b ) { printf("Received a base" ) ; } return 0 ; } Any ideas?

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  • C++ beginner question regarding chars

    - by Samwhoo
    I'm just messing around with some C++ at the moment trying to make a simple tic-tac-toe game and I'm running into a bit of a problem. This is my code: #include <iostream> using namespace std; class Square { public: char getState() const; void setState(char); Square(); ~Square(); private: char * pState; }; class Board { public: Board(); ~Board(); void printBoard() const; Square getSquare(short x, short y) const; private: Square board[3][3]; }; int main() { Board board; board.getSquare(1,2).setState('1'); board.printBoard(); return 0; } Square::Square() { pState = new char; *pState = ' '; } Square::~Square() { delete pState; } char Square::getState() const { return *pState; } void Square::setState(char set) { *pState = set; } Board::~Board() { } Board::Board() { } void Board::printBoard() const { for (int x = 0; x < 3; x++) { cout << "|"; for (int y = 0; y < 3; y++) { cout << board[x][y].getState(); } cout << "|" << endl; } } Square Board::getSquare(short x, short y) const { return board[x][y]; } Forgive me if there are blatantly obvious problems with it or it's stupidly written, this is my first program in C++ :p However, the problem is that when I try and set the square 1,2 to the char '1', it doesn't print out as a 1, it prints out as some strange character I didn't recognise. Can anyone tell me why? :) Thanks in advance.

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  • Why can't I reserve 1,000,000,000 in my vector ?

    - by vipersnake005
    When I type in the foll. code, I get the output as 1073741823. #include <iostream> #include <vector> using namespace std; int main() { vector <int> v; cout<<v.max_size(); return 0; } However when I try to resize the vector to 1,000,000,000, by v.resize(1000000000); the program stops executing. How can I enable the program to allocate the required memory, when it seems that it should be able to? I am using MinGW in Windows 7. I have 2 GB RAM. Should it not be possible? In case it is not possible, can't I declare it as an array of integers and get away? BUt even that doesn't work. Another thing is that, suppose I would use a file(which can easily handle so much data ). How can I let it read and write and the same time. Using fstream file("file.txt', ios::out | ios::in ); doesn't create a file, in the first place. But supposing the file exists, I am unable to use to do reading and writing simultaneously. WHat I mean is this : Let the contents of the file be 111111 Then if I run : - #include <fstream> #include <iostream> using namespace std; int main() { fstream file("file.txt",ios:in|ios::out); char x; while( file>>x) { file<<'0'; } return 0; } Shouldn't the file's contents now be 101010 ? Read one character and then overwrite the next one with 0 ? Or incase the entire contents were read at once into some buffer, should there not be atleast one 0 in the file ? 1111110 ? But the contents remain unaltered. Please explain. Thank you.

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  • C++ operator[] syntax.

    - by Lanissum
    Just a quick syntax question. I'm writing a map class (for school). If I define the following operator overload: template<typename Key, typename Val> class Map {... Val* operator[](Key k); What happens when a user writes: Map<int,int> myMap; map[10] = 3; Doing something like that will only overwrite a temporary copy of the [null] pointer at Key k. Is it even possible to do: map[10] = 3; printf("%i\n", map[10]); with the same operator overload?

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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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  • c# .net MVC4 Model to represent table or form

    - by Matthew Chambers
    Hello I am a little confused with regards to models in mvc 4 and thought someone may be able to point me in the right direction. This would be most appreciated. For example if i have a table that has the following fields [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 5)] public string UserName { get; set; } [Required(ErrorMessage="Email Address is Required")] [StringLength(15, ErrorMessage = "Email Address must be between {0} and {1} in size",MinimumLength = 5 )] [DataType(DataType.EmailAddress)] [Display(Name="Email")] public string Email { get; set; } [MaxLength(25)] [Display(Name="Mobile Telephone Number")] public string Mobile {get;set;} [MaxLength(500)] [Display(Name="Headline")] public string Headline {get;set;} [Required] [StringLength(200)] [Display(Name = "First Name")] public string FirstName {get;set;} [Required] [StringLength(200)] [Display(Name="Surname")] public string Surname { get; set;} public virtual int? DayOfBirthId { get; set; } public virtual DayOfBirth DayOfBirth { get; set; } public virtual int? MonthOfBirthId { get; set; } public virtual MonthOfBirth MonthOfBirth { get; set; } public virtual int? YearOfBirthId { get; set; } public virtual YearOfBirth YearOfBirth{get;set;} This is my user profile table in the database. However I would like a form that the user registers to the site with. When they first register i do not need all the details such as telephone all i really need is there username, email address and password. Do i create another model for this. Or do i have one model and on the controller set the fields to null or empty string that are not required on registration. I have validation also so would this be set for data that has not been entered on the form. My question is ultimately should all forms represent models- should the database be redesigned to meet this required. Or should the controller set the values that are not required. Or should there be another model that represents the form be created which maps to this table. I am a little confused on this and clarification of anyone would be most appreciated.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • reading root element in xml not the child

    - by Umesha MS
    Hi I am working on an application which reads XML file. Here I am trying to read the node under the not under the node . When I tried to read the I get both. Please help me to solve the problem. Bellow is the sample. "a" "x"..."/X" "b" "name" 123 "/name" "/b" "name" main "/name" "c".."/c" "/a" QDomDocument mDocument; QDomElement mDocumentElement; if (!mDocument.setContent(file.readAll())) { return ; } mDocumentElement = mDocument.documentElement(); QDomNodeList list = mDocumentElement.elementsByTagName("a").at(0).toElement().elementsByTagName("name"); int count = list.count(); for (int i = 0; i < count; i++) { QString str = list.at(i).nodeValue(); QMessageBox::information(this, "text", str, QMessageBox::Yes, 0); }

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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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  • How to convert a void pointer to array of classes

    - by user99545
    I am trying to convert a void pointer to an array of classes in a callback function that only supports a void pointer as a means of passing paramaters to the callback. class person { std::string name, age; }; void callback (void *val) { for (int i = 0; i < 9; i++) { std::cout << (person [])val[i].name; } } int main() { person p[10]; callback((void*)p); } My goal is to be able to pass an array of the class person to the callback which then prints out the data such as their name and age. However, the compile does not like what I am doing and complains that error: request for member 'name' in 'val', which is of non-class type 'void*' How can I go about doing this?

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