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• How to return a copy of the data in C++

  - by Josh Curren

  I am trying to return a new copy of the data in a C++ Template class. The following code is getting this error: invalid conversion from ‘int*’ to ‘int’. If I remove the new T then I am not returning a copy of the data but a pointer to it. template<class T> T OrderedList<T>::get( int k ) { Node<T>* n = list; for( int i = 0; i < k; i++ ) { n=n->get_link(); } return new T( n->get_data() ); // This line is getting the error ********** }

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• C# overloading with generics: bug or feature?

  - by TN

  Let's have a following simplified example: void Foo<T>(IEnumerable<T> collection, params T[] items) { // ... } void Foo<C, T>(C collection, T item) where C : ICollection<T> { // ... } void Main() { Foo((IEnumerable<int>)new[] { 1 }, 2); } Compiler says: The type 'System.Collections.Generic.IEnumerable' cannot be used as type parameter 'C' in the generic type or method 'UserQuery.Foo(C, T)'. There is no implicit reference conversion from 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.ICollection'. If I change Main to: void Main() { Foo<int>((IEnumerable<int>)new[] { 1 }, 2); } It will work ok. Why compiler does not choose the right overload?

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• MySQL pivot tables - covert rows to columns

  - by user2723490

  This is the structure of my table: Then I run a query SELECT `date`,`index_name`,`results` FROM `mst_ind` WHERE `index_name` IN ('MSCI EAFE Mid NR USD', 'Alerian MLP PR USD') AND `time_period`='M1' and get a table like How can I convert "index_name" rows to columns like: date | MSCI EAFE Mid NR USD | Alerian MLP PR USD etc In other words I need each column to represent an index and rows to represent date-result. I understand that MySQL doesn't have pivot table functions. What is the easiest way of doing this? I've tried this code, but it generates an error: SELECT `date`, MAX(IF(index_name = 'Alerian MLP PR USD' AND `time_period`='M1', results, NULL)) AS res1, MAX(IF(index_name = 'MSCI EAFE Mid NR USD' AND `time_period`='M1', results, NULL)) AS res2 FROM `mst_ind` GROUP BY `date I need to make the conversion on the query level - not PHP. Please suggest a nice and elegant solution. Thanks!

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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 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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• 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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• Casting an object which could be null

  - by DeeMac

  DateTime? testDate = (DateTime?)arrayOfObjects[dateObject]; Does that code look ok? I attempted to use the as operator but I got the 'non-nullable' error. What I'm trying to say is that the object I'm choosing from the array is either DateTime or a null DateTime but either can be assigned to testDate. Doesn't feel right doing it this way, I think I'm missing something obvious. EDIT: I suppose it's the same as the way I could've adapted the as in the following way: DateTime? testDate = arrayOfObjects[dateObject] as DateTime?; Is either line of code the best way of handling potential nulls?

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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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• Can't add an object using EF and SQL Compact

  - by kamilo

  Hello, I have some very simple SQL Compact database. I would like to use Entity Framework to access the database but for some reason I can't add an object to this database using EF. Here is the code using (pos_inglotEntities posInglotCtx = new pos_inglotEntities()) { posInglotCtx.Connection.Open(); CT_POS_OITM item = new CT_POS_OITM() { ItemCode = "123", ItemName="abc"}; try { posInglotCtx.AddToCT_POS_OITM(item); posInglotCtx.SaveChanges(); } catch (Exception e) { } posInglotCtx.Connection.Close(); } After running this code my database is still empty although if I run it once again I get "duplicate values" exception. But again database is empty. I created this db using PrimeWorks conversion tool from standard sql server database. What is going on? Thanks in advance

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• C++: use array of strings wrapped in namespace?

  - by John D.

  I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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• SSIS Script Component + Helper Assemblies (.dll's)

  - by Nev_Rahd

  I got a script component which does Transformation / DataType conversions / Creating some calculated columns. All the transform validations / datatype conversion methods and for new column generation is put into custom .dll. As this script component would be same for all other tables, only thing is to define input / ouput columns and apply validation methods on required columns. This all works fine. On production server where do I need to deploy my .dll. Would just putting it into GAC will be enough or need to do something else. Regards

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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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• Beginner C++ Question

  - by Donal Rafferty

  I have followed the code example here toupper c++ example And implemented it in my own code as follows void CharString::MakeUpper() { char* str[strlen(m_pString)]; int i=0; str[strlen(m_pString)]=m_pString; char* c; while (str[i]) { c=str[i]; putchar (toupper(c)); i++; } } But this gives me the following compiler error CharString.cpp: In member function 'void CharString::MakeUpper()': CharString.cpp:276: error: invalid conversion from 'char*' to 'int' CharString.cpp:276: error: initializing argument 1of 'int toupper(int)' CharString.cpp: In member function 'void CharString::MakeLower()': This is line 276 putchar (toupper(c)); I understand that toupper is looking for int as a parameter and returns an int also, is that the problem? If so how does the example work?

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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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• 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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• 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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• c# short if statement not working with int? (int=null)

  - by kobe

  I am trying to shorten my code by using short-if: int? myInt=myTextBox.Text == "" ? null : Convert.ToInt32(myTextBox.Text); But I'm getting the following error: Type of conditional expression cannot be determined because there is no implicit conversion between '' and 'int' The following works: int? myInt; if (myTextBox.Text == "") //if no text in the box myInt=null; else myInt=Convert.ToInt32(myTextBox.Text); And if I replace the 'null' in integer (say '4') it also works: int? myInt=myTextBox.Text == "" ? 4: Convert.ToInt32(myTextBox.Text);

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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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• 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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• 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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• 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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• 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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• What does it mean when a Perl method returns a "hashref"?

  - by Uri

  I'm trying to decrypt a Perl code which I'm not familiar with, somehow related to HashRef. I'm using Amazon::S3, but my question is a general Perl question. See the code below: use Amazon::S3; my $s3 = Amazon::S3->new( ... ); my $response = $s3->buckets; Documentation (here) sais, about s3-buckets: Returns undef on error, else HASHREF of results The following line is working for me, but I don't understand why: for $b in ( @ { $response->{buckets} } ) { print "bucket: " . $b->bucket . "\n"; } I'm Puzzled by each operator on the first line. What type exactly are $response, $respone->{bucket}. Looks like the expression within the for is an array, but I don't understand this syntax: @{ ... }?

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• C++ - repeatedly using istringstream

  - by Goffrey

  I have a code for reading files with float numbers on line stored like this: "3.34|2.3409|1.0001|...|1.1|". I would like to read them using istringstream, but it doesn't work as I would expect: string row; string strNum; istringstream separate; // textovy stream pro konverzi while ( getline(file,row) ) { separate.str(row); // = HERE is PROBLEM = while( getline(separate, strNum, '|') ) { // using delimiter flNum = strToFl(strNum); // my conversion insertIntoMatrix(i,j,flNum); // some function j++; } i++; } In marked point, row is copied into separate stream only first time. In next iteration it doesn't work and it does nothing. I expected it is possible to be used more times without constructing new istringstream object in every iteration.

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• problem with sql statement using vb.net

  - by newBie

  hi i got some problem i got this 3 line statement: Dim infoID As Integer = objCommand1.ExecuteScalar() Dim strSQL2 As String = "insert into feedBackHotel (infoID, feedBackView) values(" + infoID + ",'" + FeedBack + "')" Dim objCommand2 As New SqlCommand(strSQL2, conn) objCommand2.ExecuteNonQuery() the problem here is..the strSQL2 can capture the infoID from previous statement, but it didnt insert into the database. it will pop out this error "Conversion from string "insert into feedBackHotel (infoI" to type 'Double' is not valid." in both table related, use same data type (int) but for the feedBackHotel's infoID i allow it to be null..bcoz if i make it not null, it will show another error.. im using vb.net ..can anyone help?

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