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  • Trying to overload + operator

    - by FrostyStraw
    I cannot for the life of me understand why this is not working. I am so confused. I have a class Person which has a data member age, and I just want to add two people so that it adds the ages. I don't know why this is so hard, but I'm looking for examples and I feel like everyone does something different, and for some reason NONE of them work. Sometimes the examples I see have two parameters, sometimes they only have one, sometimes the parameters are references to the object, sometimes they're not, sometimes they return an int, sometimes they return a Person object. Like..what is the most normal way to do it? class Person { public: int age; //std::string haircolor = "brown"; //std::string ID = "23432598"; Person(): age(19) {} Person operator+(Person&) { } }; Person operator+(Person &obj1, Person &obj2){ Person sum = obj1; sum += obj2; return sum; } I really feel like overloading a + operator should seriously be the easiest thing in the world except I DON'T KNOW WHAT I AM DOING. I don't know if I'm supposed to create the overload function inside the class, outside, if it makes a difference, why if I do it inside it only allows one parameter, I just honestly don't get it.

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  • Visitor and templated virtual methods

    - by Thomas Matthews
    In a typical implementation of the Visitor pattern, the class must account for all variations (descendants) of the base class. There are many instances where the same method content in the visitor is applied to the different methods. A templated virtual method would be ideal in this case, but for now, this is not allowed. So, can templated methods be used to resolve virtual methods of the parent class? Given (the foundation): struct Visitor_Base; // Forward declaration. struct Base { virtual accept_visitor(Visitor_Base& visitor) = 0; }; // More forward declarations struct Base_Int; struct Base_Long; struct Base_Short; struct Base_UInt; struct Base_ULong; struct Base_UShort; struct Visitor_Base { virtual void operator()(Base_Int& b) = 0; virtual void operator()(Base_Long& b) = 0; virtual void operator()(Base_Short& b) = 0; virtual void operator()(Base_UInt& b) = 0; virtual void operator()(Base_ULong& b) = 0; virtual void operator()(Base_UShort& b) = 0; }; struct Base_Int : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Long : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Short : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UInt : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_ULong : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UShort : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; Now that the foundation is laid, here is where the kicker comes in (templated methods): struct Visitor_Cout : public Visitor { template <class Receiver> void operator() (Receiver& r) { std::cout << "Visitor_Cout method not implemented.\n"; } }; Intentionally, Visitor_Cout does not contain the keyword virtual in the method declaration. All the other attributes of the method signatures match the parent declaration (or perhaps specification). In the big picture, this design allows developers to implement common visitation functionality that differs only by the type of the target object (the object receiving the visit). The implementation above is my suggestion for alerts when the derived visitor implementation hasn't implement an optional method. Is this legal by the C++ specification? (I don't trust when some says that it works with compiler XXX. This is a question against the general language.)

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  • Table and Column names causing problems

    - by craig
    I have an issue when the T4 linq templates generate the classes for my MySql db using subsonic 3. It looks like one of our table names "operator" is causing problems in the Context.cs generated class. In the following line of code in Context.cs Visual Studio sees <operator> as a c# operator and generates a compilation error of "Type expected" public Query<operator> operators { get; set; } Is there anyway I can work around this without having to rename my database table and column names? For example hard coding something in Settings.ttinclude to use or map different names to specific db tables and columns?

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  • explicit copy constructor or implicit parameter by value

    - by R Samuel Klatchko
    I recently read (and unfortunately forgot where), that the best way to write operator= is like this: foo &operator=(foo other) { swap(*this, other); return *this; } instead of this: foo &operator=(const foo &other) { foo copy(other); swap(*this, copy); return *this; } The idea is that if operator= is called with an rvalue, the first version can optimize away construction of a copy. So when called with a rvalue, the first version is faster and when called with an lvalue the two are equivalent. I'm curious as to what other people think about this? Would people avoid the first version because of lack of explicitness? Am I correct that the first version can be better and can never be worse?

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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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  • Overloading new, delete in C++

    - by user265260
    i came across this line is stroustrup An operator function must either be a member or take at least one argument of a user-defined type (functions redefining the new and delete operators need not). Dont operator new and operator delete take an user defined type as one of their arguments? what does it mean, am i missing something here

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  • C++ Code Clarification Needed..

    - by ke3pup
    Hi guys I'm trying to understand what the code below says: struct compare_pq; struct compare_pq { bool operator() (Events *& a, Events *& b); }; std::priority_queue<Events *, std::vector<Events *>, compare_pq> eventList; i looked at what priority_queue is and how its declared but can't quit understand what compare_pq is doing in the priority_queue eventList. Also what does operator() do since i've never seen *& before and empty operator overloading operator()! any help would be appreciated. Thank you

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  • What is the best signature for overloaded arithmetic operators in C++?

    - by JohnMcG
    I had assumed that the canonical form for operator+, assuming the existence of an overloaded operator+= member function, was like this: const T operator+(const T& lhs, const T& rhs) { return T(lhs) +=rhs; } But it was pointed out to me that this would also work: const T operator+ (T lhs, const T& rhs) { return lhs+=rhs; } In essence, this form transfers creation of the temporary from the body of the implementation to the function call. It seems a little awkward to have different types for the two parameters, but is there anything wrong with the second form? Is there a reason to prefer one over the other?

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  • What does the caret operator in Python do?

    - by Fry
    I ran across the caret operator in python today and trying it out, I got the following output: >>> 8^3 11 >>> 8^4 12 >>> 8^1 9 >>> 8^0 8 >>> 7^1 6 >>> 7^2 5 >>> 7^7 0 >>> 7^8 15 >>> 9^1 8 >>> 16^1 17 >>> 15^1 14 >>> It seems to be based on 8, so I'm guessing some sort of byte operation? I can't seem to find much about this searching sites other than it behaves oddly for floats, does anybody have a link to what this operator does or can you explain it here?

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  • String concatenation: Final string value does not equal to the latest value

    - by Pan Pizza
    I have a simple question about string concatenation. Following is the code. I want to ask why s6 = "abcde" and not "akcde"? I have change the s2 value to "k". Public Class Form1 Public s1 As String = "a" Public s2 As String = "b" Public s3 As String = "c" Public s4 As String = "d" Public s5 As String = "e" Public s6 As String = "" Public s7 As String = "k" Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click s6 = s1 & s2 & s3 & s4 & s5 s2 = s7 MessageBox.Show(s6) 's6 = abcde End Sub End Class

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  • Conditional Operator in SQL Where Clause

    - by Marc
    I'm wishing I could do something like the following in SQl Server 2005 (which I know isnt valid) for my where clause. Sometimes @teamID (passed into a stored procedure) will be the value of an existing teamID, otherwise it will always be zero and I want all rows from the Team table. I researched using Case and the operator needs to come before or after the entire statement which prevents me from having a different operator based on the value of @teamid. Any suggestions other than duplicating my select statements. declare @teamid int set @teamid = 0 Select Team.teamID From Team case @teamid when 0 then WHERE Team.teamID > 0 else WHERE Team.teamID = @teamid end

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  • Can operator= may be not a member?

    - by atch
    Having construction in a form: struct Node { Node():left_(nullptr), right_(nullptr) { } int id_; Node* left_; Node* right_; }; I would like to enable syntax: Node parent; Node child; parent.right_ = child; So in order to do so I need: Node& operator=(Node* left, Node right); but I'm getting msg that operator= has to be a member fnc; Is there any way to circumvent this restriction?

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  • Regex not equal to string

    - by Kieron
    Hi, I'm banging my head against a wall with a regular expression. I'm trying to define an expression that excludes exactly this text 'System' (case insensitive), but can contain the word 'System' providing it's not just that. Examples: System == INVALID SYSTEM == INVALID system == INVALID syStEm == INVALID asd SysTem == Valid asd System asd == Valid System asd == Valid asd System == Valid asd == Valid

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  • Using Logger Filter with Not Equal condition Log4net

    - by Mubashar Ahmad
    Dears I am using log4net in my c# application i have different logger which insert text lines in my single log file. But now i wanted to add a new logger which should not post log entries in the same file rather i should log in a different file so i configured a new fileAppender, After doing whatever i found on the net i am able to create a different file for my new logger but it echoes the same value in first log file too. so please if anybody knows about the use of LogFilters so that i could add "Logger < New logger " match in previously configured appender. Regards Mubashar

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  • Is a switch statement the fastest way to implement operator interpretation in Java

    - by Mordan
    Is a switch statement the fastest way to implement operator interpretation in Java public boolean accept(final int op, int x, int val) { switch (op) { case OP_EQUAL: return x == val; case OP_BIGGER: return x > val; case OP_SMALLER: return x < val; default: return true; } } In this simple example, obviously yes. Now imagine you have 1000 operators. would it still be faster than a class hierarchy? Is there a threshold when a class hierarchy becomes more efficient in speed than a switch statement? (in memory obviously not) abstract class Op { abstract public boolean accept(int x, int val); } And then one class per operator.

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  • Set Height of Div Equal to Parent Tag

    - by Phong Dang
    Hello, I have a snip code HTML as below : <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns:o="urn:schemas-microsoft-com:office:office" lang="en-us" dir="ltr"> <head> <meta http-equiv="X-UA-Compatible" content="IE=8" /> <meta name="GENERATOR" content="Microsoft SharePoint" /> <meta name="progid" content="SharePoint.WebPartPage.Document" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta http-equiv="Expires" content="0" /> <title>Demo </title> <style type="text/css"> A { font-weight: normal; font-size: 10pt; text-decoration: none; } </style> <link rel="stylesheet" type="text/css" href="/_layouts/1033/styles/Themable/wiki.css?rev=AWRyZDbGxZSekWBubaxPXw%3D%3D" /> <link rel="stylesheet" type="text/css" href="/_layouts/1033/styles/Themable/corev4.css?rev=w9FW7ASZnUjiWWCtJEcnTw%3D%3D" /> </head> <body topmargin="0" leftmargin="0" marginheight="0" marginwidth="0" style="height:100%;"> <form method="" name="frm"> <table style="border-bottom: black 1px solid; border-left: black 1px solid; border-collapse: collapse; border-top: black 1px solid; border-right: black 1px solid" id="ctl00_m_g_510fd150_a968_41ee_a28d_d47ff4a7198e_BambooCalendarControl" height="100%"> <tbody> <tr> <td style="border-top: black 1px solid; border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> <span> <nobr>8:00 AM</nobr> </span> </td> <td style="border-bottom: #d4d0c8 1px dotted; background-color: #ccffcc; border-left: 0px; border-top: black 1px solid; border-right: black 1px solid" height="100%" valign="top" rowspan="8" width="50%"> <div style="border-bottom: gray 1px solid; border-left: gray 1px solid; background-color: #ffa500; height: 100%; overflow: hidden; border-top: gray 1px solid; border-right: gray 1px solid" nowrap width="100%" valign="top"> <a style="height: 100%; color: black" href="#"><font color="white">Item </font></a> </div> </td> <td style="border-bottom: #d4d0c8 1px dotted; border-left: 0px; border-top: black 1px solid; border-right: black 1px solid" height="25" valign="top" width="100%" colspan="1"> </td> </tr> <tr> <td style="border-bottom: black 1px solid; border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> </td> <td style="border-bottom: black 1px solid; border-left: 0px; border-right: black 1px solid" height="25" valign="top" width="100%" colspan="1"> </td> </tr> <tr> <td style="border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> <span> <nobr>9:00 AM</nobr> </span> </td> <td style="border-bottom: #d4d0c8 1px dotted; background-color: #ccffcc; border-left: 0px; border-right: black 1px solid" height="100%" valign="top" rowspan="4" width="50%"> <div style="border-bottom: gray 1px solid; border-left: gray 1px solid; background-color: #bdb76b; height: 100%; overflow: hidden; border-top: gray 1px solid; border-right: gray 1px solid" nowrap width="100%" valign="top"> <a style="height: 100%; color: black" title="" href="#"><font color="white">Item 2 </font> </a> </div> </td> </tr> <tr> <td style="border-bottom: black 1px solid; border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> </td> </tr> <tr style="border-left: medium none; border-right: #696969 1px solid"> <td style="border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> <span> <nobr>10:00 AM</nobr> </span> </td> </tr> <tr> <td style="border-bottom: black 1px solid; border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> </td> </tr> <tr> <td style="border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> <span> <nobr>11:00 AM</nobr> </span> </td> <td style="border-bottom: #d4d0c8 1px dotted; border-left: 0px; border-top: black 1px solid; border-right: black 1px solid" height="25" valign="top" width="100%" colspan="1"> </td> </tr> <tr> <td style="border-bottom: black 1px solid; border-right: black 1px solid" height="25" valign="top" rowspan="1" width="1%" align="right"> </td> <td style="border-bottom: black 1px solid; border-left: 0px; border-right: black 1px solid" height="25" valign="top" width="100%" colspan="2"> </td> </tr> </tbody> </table> </form> </body> </html> I set the height of the div 100% so that it full of TD but it did not effect. Please help me ! Thanks / PD

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  • jQuery Equal Height Divs

    - by griegs
    If i have the following harkup; <div> <div> <div id='sameHeight'>One<br>two<br>three</div> <div id='sameHeight'>four</div> <div id='sameHeight'>five</div> <div> <div> <div id='sameHeight'>four</div> <div id='sameHeight'>six</div> <div id='sameHeight'>seven<br>eight</div> <div> </div> How can I ensure that all divs marked as "sameHeight" are the same height as their counterparts in the other div? I had a look at equalHeights plugin but that assumes all divs side by side are in the same parent. I need one that can either traverse parents or allow me to specify parents. Is there such a thing or do I need to write it?

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  • NSNumber floatValue not equal to NSNumber value

    - by Mirkules
    Hi Everyone, First post here. Having a problem with NSNumber's floatValue method -- somehow, it returns an imprecise number. Here's the problem: I store a bunch of NSNumbers in an array, like this: NSArray *a = [NSArray arrayWithObjects: [NSNumber numberWithFloat:0.04f], [NSNumber numberWithFloat:0.028f], [NSNumber numberWithFloat:0.016f], [NSNumber numberWithFloat:0.004f], nil]; Then I try to retrieve the first value (for example): NSNumber n = (NSNumber) [a objectAtIndex:0]; CGFloat f = [n floatValue]; In the debugger, n shows a value of 0.04 (in the summary column), but f shows a value of 0.0399999991. What am I doing wrong here? Thanks everyone.

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  • Making one table equal to another without a delete *

    - by Joshua Atkins
    Hey, I know this is bit of a strange one but if anyone had any help that would be greatly appreciated. The scenario is that we have a production database at a remote site and a developer database in our local office. Developers make changes directly to the developer db and as part of the deployment process a C# application runs and produces a series of .sql scripts that we can execute on the remote side (essentially delete *, insert) but we are looking for something a bit more elaborate as the downtime from the delete * is unacceptable. This is all reference data that controls menu items, functionality etc of a major website. I have a sproc that essentially returns a diff of two tables. My thinking is that I can insert all the expected data in to a tmp table, execute the diff, and drop anything from the destination table that is not in the source and then upsert everything else. The question is that is there an easy way to do this without using a cursor? To illustrate the sproc returns a recordset structured like this: TableName Col1 Col2 Col3 Dest Src Anything in the recordset with TableName = Dest should be deleted (as it does not exist in src) and anything in Src should be upserted in to dest. I cannot think of a way to do this purely set based but my DB-fu is weak. Any help would be appreciated. Apologies if the explanation is sketchy; let me know if you need anymore details.

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