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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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  • 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 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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  • 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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  • ILNumerics multiply complex with matrix<double>

    - by nik
    I m looking at ILNumerics to translate some matlab code into c#. How would I multiply a complex and a double? Simplified description: In Matlab: A=[1 2 3] i*A*A' Returns a complex number. How would I do the same in ILNumerics: ILArray<double> A = ILMath.array(1.0, 2.0, 3.0); complex B = complex.i * ILMath.multiply(A,A.T); Throws the error: Operator '*' cannot be applied to operands of type 'ILNumerics.complex' and 'ILNumerics.ILRetArray<double>' Update This works: double C = 14.0; complex D = complex.i * C; But shouldnt: ILMath.multiply(A,A.T) also return 14.0?

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  • MySQL Join Comma Separated Field

    - by neeraj
    I have two tables. First Table is a batch table that contain comma separated student id in field "batch" batch -------------- id batch -------------- 1 1,2 2 3,4 Second Table is marks marks ---------------------- id studentid subject marks 1 1 English 50 2 2 English 40 3 3 English 70 4 1 Math 65 5 4 English 66 6 5 English 75 7 2 Math 55 How we can find those students of first batch id =1 who have scored more than 45 marks in English without using sub query. Problem i found to get this done using a single query is that we can not use IN as an association operator in JOIN statement What changes are required in below query to make it work? SELECT * FROM batch INNER JOIN marks ON marks.studentid IN(batch.batch) where batch.id = 1

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  • Mixing LINQ to SQL with properties of objects in a generic list

    - by BPotocki
    I am trying to accomplish something like this query: var query = from a in DatabaseTable where listOfObjects.Any(x => x.Id == a.Id) select a; Basically, I want to filter the results where a.Id equals a property of one of the objects in the generic list "listOfObjects". I'm getting the error "Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator." Any ideas on how to filter this in an easily readable way using "contains" or another method? Thanks in advance.

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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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  • Best way to validate currency input?

    - by Abe Miessler
    I have created the TextBox and CompareValidator below which I thought would allow input in the following forms: 5 5.00 $5.00 Unfortunately it's not allowing the version with the dollar sign in it. What is the point of doing a type check against currency if you don't allow the dollar sign? Is there a way to allow this symbol? <asp:TextBox ID="tb_CostShare" runat="server" Text='<%# Eval("CostShare", "{0:$0.00}")%>' CausesValidation="true" /> <asp:CompareValidator ID="vld_CostShare" runat="server" ControlToValidate="tb_CostShare" Operator="DataTypeCheck" Type="Currency" ValidationGroup="vld" ErrorMessage="You must enter a dollar amount for 'Cost Share'." />

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  • Purpose of IF, ELSE, FOR macros ?

    - by psihodelia
    I have a source code of a library which has a lot of strange IF, ELSE, FOR, etc. macros for all common C-keywords instead of using just usual if,else,for,while keywords. These macros are defined like this: #define IF( a) if( increment_if(), a) where increment_if() function is defined so: static __inline void increment_if( void) { // If the "IF" operator comes just after an "ELSE", its counter // must not be incremented. ... //implementation } I don't really understand, what is the purpose of such macros? This library is for a real-time application and I suppose that using such macros must slow-down an application.

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  • What is the best solution to replace a new memory allocator in an existing code?

    - by O. Askari
    During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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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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  • How to create and Expression tree to do the same as "StartsWith"

    - by Jonathan
    Hi to all. Currently, I have this method to compare two numbers Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e") Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo) Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType()) Dim b As BinaryExpression = Expression.GreaterThan(m, c) Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e) Return query.Where(lambda) End Function It works fine and is consumed in this way query = ETForGreaterThan(query, Value, propertyInfo) As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined. ¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees. Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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  • Is call to function object inlined?

    - by dehmann
    In the following code, Foo::add calls a function via a function object: struct Plus { inline int operator()(int x, int y) const { return x + y; } }; template<class Fct> struct Foo { Fct fct; Foo(Fct f) : fct(f) {} inline int add(int x, int y) { return fct(x,y); // same efficiency adding directly? } }; Is this the same efficiency as calling x+y directly in Foo::add? In other words, does the compiler typically directly replace fct(x,y) with the actual call, inlining the code, when compiling with optimizations enabled?

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  • C++ and preprocessor macro gotcha

    - by aaa
    hello. Appologies for yet another gotcha question. Can you figure out what is wrong with the statement below? gcc error states: "type name declared as function returning array". #define MACRO(a) (a)[1] class index { typedef int index_type[2]; index_type& operator[](int i); }; int k = 0; int i = MACRO(index()[k]); ps: is such questions are deemed too annoying, I am going to stop.

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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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  • What is wrong with my SQL syntax for an UPDATE with a JOIN?

    - by Phil H
    I have two tables, related by a common key. So TableA has key AID and value Name and TableB has keys AID, BID and values Name, Value: AID Name 74 Alpha AID BID Name Value 74 4 Beta Brilliance I would like to update the TableB Value here from Brilliance to Barmy, using just the Name fields. I thought I could do it via an UPDATE containing a JOIN, but Access (I know...) is complaining with 'Syntax error (missing operator) in query expression ' and then everything from 'Barmy' here: UPDATE tB SET tB.BValue='Barmy' FROM TableB tB INNER JOIN TableA tA ON tB.AID=tA.AID WHERE tB.Name='Beta' AND tA.Name='Alpha'; What is my heinous crime? Or is it just Access not conforming?

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  • C# logic order and compiler behavior

    - by Terrapin
    In C#, (and feel free to answer for other languages), what order does the runtime evaluate a logic statement? Example: DataTable myDt = new DataTable(); if (myDt != null && myDt.Rows.Count > 0) { //do some stuff with myDt } Which statement does the runtime evaluate first - myDt != null or: myDt.Rows.Count > 0 ? Is there a time when the compiler would ever evaluate the statement backwards? Perhaps when an "OR" operator is involved?

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  • C++ / Java: Toggle boolean statement?

    - by Martijn Courteaux
    Hi, Is there a short way to toggle a boolean? With integers we can do operations like this: int i = 4; i *= 4; // equals 16 /* Which is equivalent to */ i = i * 4; So is there also something for booleans (like the *= operator for ints)? In C++: bool booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something? In Java: boolean booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something?

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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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  • C++: Vector3 type "wall" ?

    - by anon
    Say I have: class Vector3 { float x, y, z; ... bunch of cuntions .. static operator+(const Vector3&, const Vector3); }; Now, suppose I want to have classes: Position, Velocity, that are exactly like Vector3 (basically, I want typedef Vector3 Position; typedef Vector3 Velocity; Except, given: Position position; Vector3 vector3; Velocity velocity; I want to make sure the following can't happen: position + vector3; vector3 + velocity; velocity + position; What is the best way to achieve this?

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  • JavaScript eval() with `this`

    - by mojuba
    If I define a JavaScript code snippet in my HTML, like so: <div id=myElem onMyUpdate="alert('Update called for ' + this.id)">... then what is the most elegant way of evaluating it from within JavaScript with this properly assigned? What I came up with so far is something like this: if (elem.hasAttribute('onMyUpdate')) (function () { eval(elem.getAttribute('onMyUpdate')) }).call(elem); which looks terrible (to me), but works. Any better/more elegant alternatives? MDN says there used to be the second argument to eval() for doing just that but it's deprecated now; MDN then suggests to use operator with() instead, which, if you follow the link provided, turns out to be made deprecated by the latest standard. Dead end, in other words. (As a side note, StackOverflow ignores the word this in search terms and thus it may miss relevant answers - is there a way of telling it not to?) Edit: I forgot to mention: no jQuery please, just vanilla JavaScript

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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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  • Assigning two strings together getting Access Read Violation

    - by Jay Bell
    I am trying to pass a string to a class mutator and set the private member to that string here is the code that is sending the string void parseTradePairs(Exchange::Currency *curr, std::string *response, int begin, int exit) { int start; int end; string temp; string dataResponse; CURL *tempCurl; initializeCurl(tempCurl); int location = response->find("marketid", begin); if(location <= exit) { start = location + 11; begin = response->find("label", start); end = begin - start - 3; findStrings(start, end, temp, response); getMarketInfo(tempCurl, temp, dataResponse); curr->_coin->setExch(temp); // here is the line of code that is sending the string dataResponse >> *(curr->_coin); curr->_next = new Exchange::Currency(curr, curr->_position + 1); parseTradePairs(curr->_next, response, begin, exit); } } and here is the mutator within the coin class that is receiving the string and assigning it to _exch void Coin::setExch(string exch) { _exch = exch; } I have stepped through it and made sure that exch has the string in it. "105" but soon as it hits _exch = exch; I get the reading violation. I tried passing as pointer as well. I do not believe it should go out of scope. and the string variable in the class is initialized to zero in the default constructor but again that should matter unless I am trying to read from it instead of writing to it. /* defualt constructor */ Coin::Coin() { _id = ""; _label = ""; _code= ""; _name = ""; _marketCoin = ""; _volume = 0; _last = 0; _exch = ""; } Exchange::Exchange(std::string str) { _exch = str; _currencies = new Currency; std::string pair; std::string response; CURL *curl; initializeCurl(curl); getTradePairs(curl, response); int exit = response.find_last_of("marketid"); parseTradePairs(_currencies, &response, 0, exit); } int main(void) { CURL *curl; string str; string id; Coin coin1; initializeCurl(curl); Exchange ex("cryptsy"); curl_easy_cleanup(curl); system("pause"); return 0; } class Exchange { public: typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() : _next(NULL), _prev(NULL), _position(0) {} Coin *_coin; Currency *_next; Currency *_prev; int _position; }; /* constructor and destructor */ Exchange(); Exchange(std::string str); ~Exchange(); /* Assignment operator */ Exchange& operator =(const Exchange& copyExchange); /* Parse Cryptsy Pairs */ friend void parseTradePairs(Currency *curr, std::string *response, int begin, int exit); private: std::string _exch; Currency *_currencies; }; here is what i changed it to to fix it. typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() { _next = NULL; _prev = NULL; _position = 0; _coin = new Coin(); } Coin *_coin; Currency *_next; Currency *_prev; int _position; };

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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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