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  • How do boost operators work?

    - by FredOverflow
    boost::operators automatically defines operators like + based on manual implementations like += which is very useful. To generate those operators for T, one inherits from boost::operators<T> as shown by the boost example: class MyInt : boost::operators<MyInt> I am familiar with the CRTP pattern, but I fail to see how it works here. Specifically, I am not really inheriting any facilities since the operators aren't members. boost::operators seems to be completely empty, but I'm not very good at reading boost source code. Could anyone explain how this works in detail? Is this mechanism well-known and widely used?

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  • how to handle delete by illegal address

    - by Davit Siradeghyan
    Suppose we have a situation like this. How to handle this problem? How to protect code from crashes? I know about and use boost smart pointers. But what to do if we have this situation. struct Test { int a; int b; int c; }; Test global; int main() { Test *p = new Test; p->a = 1; p->b = 2; p->c = 3; p = &global; delete p; return 0; }

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  • Why is this code invalid in C#?

    - by mmattax
    The following code will not compile: string foo = "bar"; Object o = foo == null ? DBNull.Value : foo; I get: Error 1 Type of conditional expression cannot be determined because there is no implicit conversion between 'System.DBNull' and 'string' To fix this, I must do something like this: string foo = "bar"; Object o = foo == null ? DBNull.Value : (Object)foo; This cast seems pointless as this is certainly legal: string foo = "bar"; Object o = foo == null ? "gork" : foo; It seems to me that when the ternary branches are of different types, the compiler will not autobox the values to the type object...but when they are of the same type then the autoboxing is automatic. In my mind the first statement should be legal... Can anyone describe why the compiler does not allow this and why the designers of C# chose to do this? I believe this is legal in Java...Though I have not verified this. Thanks. EDIT: I am asking for an understanding of why Java and C# handle this differently, what is going on underneath the scenes in C# that make this invalid. I know how to use ternary, and am not looking for a "better way" to code the examples. I understand the rules of ternary in C#, but I want to know WHY... EDIT (Jon Skeet): Removed "autoboxing" tag as no boxing is involved in this question.

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  • Bitwise AND, Bitwise Inclusive OR question, in Java

    - by Dave
    I've a few lines of code within a project, that I can't see the value of... buffer[i] = (currentByte & 0x7F) | (currentByte & 0x80); It reads the filebuffer from a file, stored as bytes, and then transfers then to buffer[i] as shown, but I can't understand what the overall purpose is, any ideas? Thanks

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  • What does "<<" mean in C#?

    - by Simon G
    Hi, Basically the questions in the title. I'm looking at the MVC 2 source code: public enum HttpVerbs { Get = 1 << 0, Post = 1 << 1, Put = 1 << 2, Delete = 1 << 3, Head = 1 << 4 } and I'm just curious as to what "<<" does. Thanks

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  • Implementing __concat__

    - by Casebash
    I tried to implement __concat__, but it didn't work >>> class lHolder(): ... def __init__(self,l): ... self.l=l ... def __concat__(self, l2): ... return self.l+l2 ... def __iter__(self): ... return self.l.__iter__() ... >>> lHolder([1])+[2] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'lHolder' and 'list' How can I fix this?

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  • Should I use `!IsGood` or `IsGood == false`?

    - by chills42
    I keep seeing code that does checks like this if (IsGood == false) { DoSomething(); } or this if (IsGood == true) { DoSomething(); } I hate this syntax, and always use the following syntax. if (IsGood) { DoSomething(); } or if (!IsGood) { DoSomething(); } Is there any reason to use '== true' or '== false'? Is it a readability thing? Do people just not understand Boolean variables? Also, is there any performance difference between the two?

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  • SQL searching table fields with LIKE

    - by Tom Gullen
    Given your data stored somewhere in a database: Hello my name is Tom I like dinosaurs to talk about SQL. SQL is amazing. I really like SQL. We want to implement a site search, allowing visitors to enter terms and return relating records. A user might search for: Dinosaurs And the SQL: WHERE articleBody LIKE '%Dinosaurs%' Copes fine with returning the correct set of records. How would we cope however, if a user mispells dinosaurs? IE: Dinosores (Poor sore dino). How can we search allowing for error in spelling? We can associate common misspellings we see in search with the correct spelling, and then search on the original terms + corrected term, but this is time consuming to maintain. Any way programatically?

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  • Dictionary keys don't contain a key that's already contained in keys

    - by ran
    Why is the following 'exist' boolean variable getting a value of false??? foreach (Cell existCell in this.decoratorByCell.Keys) { //this call yield the same hashcode for both cells. still exist==false bool exist = this.decoratorByCell.ContainsKey(existCell); } I've overridden GetHashCode() & Equals() Methods as follows: public override int GetHashCode() { string nodePath = GetNodePath(); return nodePath.GetHashCode() + m_ownerColumn.GetHashCode(); } public bool Equals(Cell other) { bool nodesEqual = (other.OwnerNode == null && this.OwnerNode == null) || (other.GetNodePath() == this.GetNodePath()); bool columnsEqual = (other.OwnerColumn == null && this.OwnerColumn == null) || (other.OwnerColumn == this.OwnerColumn); bool treesEqual = (this.m_ownerTree == other.m_ownerTree); return (nodesEqual && columnsEqual && treesEqual); }

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  • Linked List pop() function

    - by JKid314159
    Consider the following list: [LinkNode * head -- LinkNode * node1 -- LinkNode * node2] I'm creating a stack of FIFO. I Call pop() which I want to pop node1. LinkNode::LinkNode(int numIn) { this->numIn = numIn; next = null; } . . . int LinkNode::pop() { Link * temp = head->next; head = temp->next; int popped = head->nodeNum; delete temp; Return numOut; Question: 1) head should be a pointer or a LinkNode *? 2) Link * temp is created on the call stack and when pop finishes doesn't temp delete automatically? 3) My major confusion is on what is the value of temp-next? Does this point to node1.next which equals node2? Appreciate your help? My reference is C++ for Java Programmers by Weiss.

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  • Two '==' equality operators in same 'if' condition are not working as intended.

    - by Manav MN
    I am trying to establish equality of three equal variables, but the following code is not printing the obvious true answer which it should print. Can someone explain, how the compiler is parsing the given if condition internally? #include<stdio.h> int main() { int i = 123, j = 123, k = 123; if ( i == j == k) printf("Equal\n"); else printf("NOT Equal\n"); return 0; } Output: manav@workstation:~$ gcc -Wall -pedantic calc.c calc.c: In function ‘main’: calc.c:5: warning: suggest parentheses around comparison in operand of ‘==’ manav@workstation:~$ ./a.out NOT Equal manav@workstation:~$ EDIT: Going by the answers given below, is the following statement okay to check above equality? if ( (i==j) == (j==k))

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  • VB.NET overloading array access?

    - by Wayne Werner
    Hi, Is it possible to overload the array/dict access operators in VB.net? For example, you can state something like: Dim mydict As New Hashtable() mydict.add("Cool guy", "Overloading is dangerous!") mydict("Cool guy") = "Overloading is cool!" And that works just fine. But what I would like to do is be able to say: mydict("Cool guy") = "3" and then have 3 automagically converted to the Integer 3. I mean, sure I can have a private member mydict.coolguy and have setCoolguy() and getCoolguy() methods, but I would prefer to be able to write it the former way if at all possible. Thanks

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  • Index, assignment and increment in one statement behaves differently in C++ and C#. Why?

    - by Ivan Zlatanov
    Why is this example of code behaving differently in c++ and C#. [C++ Example] int arr[2]; int index = 0; arr[index] = ++index; The result of which will be arr[1] = 1; [C# Example] int[] arr = new int[2]; int index = 0; arr[index] = ++index; The result of which will be arr[0] = 1; I find this very strange. Surely there must be some rationale for both languages to implement it differently? I wonder what would C++/CLI output?

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  • Linq like or other construction

    - by Yauhen Kavalenka
    I have DB oracle in my solution. I want to have some results in this query. Query example: select * from doctor where doctor.name like '%IVANOV_A%'; But if i do it at LINQ i cannot get any result. from p in repository.Doctor.Where(x => x.Name.ToLower().Containsname)) select p; Where 'name' is variable of string parameter. Web layout request next string: "Ivanov a" or "A Ivanov" But i suggest for user choose you pattetn for query. How i can to get "patient by name" if name consist of "First name" and "Last name" but user doesn't know your doctor's full name?

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  • MySQL: Which is faster — INSTR or LIKE?

    - by Grekker
    If your goal is to test if a string exists in a MySQL column (of type 'varchar', 'text', 'blob', etc) which of the following is faster / more efficient / better to use, and why? Or, is there some other method that tops either of these? INSTR( columnname, 'mystring' ) > 0 vs columnname LIKE '%mystring%'

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  • c++ how to ? function_x ( new object1 )

    - by ismail marmoush
    Hi i want to do the next instead of MyClass object; function_x (object); i want to function_x ( new object ); so what will be the structure of the MyClass to be able to do that .. if i just compiled it , it gives me a compile time error answer function_x (MyClass() ) New Edit thanks for the quick answers.. i did ask the wrong Question i should have asked how temporary variables created in C++ and the answer

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  • Optimize conditional operators branching in C#

    - by abatishchev
    Hello. I have next code: return this.AllowChooseAny.Value ? radioSpecific.Checked ? UserManager.CurrentUser.IsClient ? txtSubject.Text : subjectDropDownList.SelectedItem.Text : String.Empty : UserManager.CurrentUser.IsClient ? txtSubject.Text : subjectDropDownList.SelectedItem.Text; or in less complex form: return any ? specified ? isClient ? textbox : dropdown : empty : isClient ? textbox : dropdown; or in schematic form: | any / \ specified isClient / \ / \ isClient empty textbox dropdown / \ textbox dropdown Evidently I have a duplicated block on two different levels. Is it possible to optimize this code to probably split them to one? Or something like that..

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  • C++ brain teaser

    - by mxp
    I recently refactored code like this (MyClass to MyClassR). class SomeMember { long m_value; public: SomeMember() : m_value(0) {} SomeMember(int a) : m_value(a) {} SomeMember(int a, int b) : m_value(a+b) {} }; class MyClass { SomeMember m_first, m_second, m_third; public: MyClass(const bool isUp, const int x, const int y) { if (isUp) { m_first = SomeMember(x); m_second = SomeMember(y); m_third = SomeMember(x, y); } else { m_first = SomeMember(y); m_second = SomeMember(x); m_third = SomeMember(y, x); } } }; class MyClassR { SomeMember m_first, m_second, m_third; public: MyClassR(const bool isUp, const int x, const int y) : m_first(isUp ? x : y) , m_second(isUp ? y : x) , m_third(isUp ? x, y : y, x) { } }; What is the error, why does it compile (at least VC6 with warning level 3 doesn't complain) and what is the right way of doing it? I (assume) I already have all these answers but I think it's and interesting problem to share.

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  • Checking instance of non-class constrained type parameter for null in generic method

    - by casperOne
    I currently have a generic method where I want to do some validation on the parameters before working on them. Specifically, if the instance of the type parameter T is a reference type, I want to check to see if it's null and throw an ArgumentNullException if it's null. Something along the lines of: // This can be a method on a generic class, it does not matter. public void DoSomething<T>(T instance) { if (instance == null) throw new ArgumentNullException("instance"); Note, I do not wish to constrain my type parameter using the class constraint. I thought I could use Marc Gravell's answer on "How do I compare a generic type to its default value?", and use the EqualityComparer<T> class like so: static void DoSomething<T>(T instance) { if (EqualityComparer<T>.Default.Equals(instance, null)) throw new ArgumentNullException("instance"); But it gives a very ambiguous error on the call to Equals: Member 'object.Equals(object, object)' cannot be accessed with an instance reference; qualify it with a type name instead How can I check an instance of T against null when T is not constrained on being a value or reference type?

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