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• C# LINQ to SQL Except Operator

  - by kb

  Hi i have a list of event Ids that i want to be excluded from my select statement, but no sure how to implement this: this is what stores my list of event Ids List<int> ExcludedEvents; and this is my select statement (from an XML feed) var allEvents = from eventsList in xmlDoc.Elements("shows").Elements("Show") select new EventFeed() { EventName = eventsList.Attribute("Name").Value, EventSummary = eventsList.Attribute("ShortDesc").Value, EventDetails = eventsList.Attribute("LongDesc").Value, EventShowCode = eventsList.Attribute("Code").Value }; i want to select all events except for the events that have their eventId matching the EventShowCode value i have looked at the except operator, but not sure how to implement it thanks

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• Scheme Infix to Postfix

  - by Cody

  Let me establish that this is part of a class assignment, so I'm definitely not looking for a complete code answer. Essentially we need to write a converter in Scheme that takes a list representing a mathematical equation in infix format and then output a list with the equation in postfix format. We've been provided with the algorithm to do so, simple enough. The issue is that there is a restriction against using any of the available imperative language features. I can't figure out how to do this in a purely functional manner. This is our fist introduction to functional programming in my program. I know I'm going to be using recursion to iterate over the list of items in the infix expression like such. (define (itp ifExpr) ( ; do some processing using cond statement (itp (cdr ifExpr)) )) I have all of the processing implemented (at least as best I can without knowing how to do the rest) but the algorithm I'm using to implement this requires that operators be pushed onto a stack and used later. My question is how do I implement a stack in this function that is available to all of the recursive calls as well?

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• Perl file test operator help

  - by Aaron Moodie

  This is a really basic issue, but I'm new to perl and cannot work out what the issue is. I'm just trying to isolate the files in a directory, but the -d operator keeps treating all the folder contents as files ... @contents is my array, and when I run this: foreach $item(@contents) { if (-d $item) { next; } print"$item is a file\n"; } I keep getting both folders and files. Alternatively, if I use -f, I get nothing. edit: this is the output - file01.txt is a file folder 01 is a file folder 02 is a file Screen shot 2010-04-18 at 1.26.17 PM.png is a file I'm running this on OSX

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• Prototype Library use of !! operator

  - by Rajat

  Here is a snippet from Prototype Javascript Library : Browser: (function(){ var ua = navigator.userAgent; var isOpera = Object.prototype.toString.call(window.opera) == '[object Opera]'; return { IE: !!window.attachEvent && !isOpera, Opera: isOpera, WebKit: ua.indexOf('AppleWebKit/') > -1, Gecko: ua.indexOf('Gecko') > -1 && ua.indexOf('KHTML') === -1, MobileSafari: /Apple.*Mobile/.test(ua) } })(), This is all good and i understand the objective of creating a browser object. One thing that caught my eye and I haven't been able to figure out is the use of double not operator !! in the IE property. If you read through the code you will find it at many other places. I dont understand whats the difference between !!window.attachEvent and using just window.attachEvent. Is it just a convention or is there more to it that's not obvious?

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• std::string == operator not working

  - by Paul

  Hello, I've been using std::string's == operator for years on windows and linux. Now I am compiling one of my libraries on linux, it uses == heavily. On linux the following function fails, because the == returns false even when the strings are equal (case sensitive wise equal) const Data* DataBase::getDataByName( const std::string& name ) const { for ( unsigned int i = 0 ; i < m_dataList.getNum() ; i++ ) { if ( m_dataList.get(i)->getName() == name ) { return m_dataList.get(i); } } return NULL; } The getName() method is declared as follows virtual const std::string& getName() const; I am building with gcc 4.4.1 and libstdc++44-4.4.1. Any ideas? it looks perfectly valid to me. Paul

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• Parallel Assignment operator in Ruby

  - by Bragaadeesh

  Hi, I was going through an example from Programming in Ruby book. This is that example def fib_up_to(max) i1, i2 = 1, 1 # parallel assignment (i1 = 1 and i2 = 1) while i1 <= max yield i1 i1, i2 = i2, i1+i2 end end fib_up_to(100) {|f| print f, " " } The above program simply prints the fibonacci numbers upto 100. Thats fine. My question here is when i replace the parallel assignment with something like this, i1 = i2 i2 = i1+i2 I am not getting the desired output. My question here is, is it advisable to use parallel assignments? (I come from Java background and it feels really wierd to see this type of assignment) One more doubt is : Is parallel assignment an operator?? Thanks

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• What's the purpose of having a separate "operator new[]" ?

  - by sharptooth

  Looks like operator new and operator new[] have exactly the same signature: void* operator new( size_t size ); void* operator new[]( size_t size ); and do exactly the same: either return a pointer to a big enough block of raw (not initialized in any way) memory or throw an exception. Also operator new is called internally when I create an object with new and operator new[] - when I create an array of objects with new[]. Still the above two special functions are called by C++ internally in exactly the same manner and I don't se how the two calls can have different meanings. What's the purpose of having two different functions with exactly the same signatures and exactly the same behavior?

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• The data types text and nvarchar are incompatible in the equal to operator

  - by metro

  Hi there. this is my code ProductController.cs public ActionResult Details(string id) { product productx = productDB.products.Single(pr => pr.Product1 == id); return View(productx); } Details.aspx <td> <%-- : Html.ActionLink("Edit", "Edit", new { id=item.Id }) % --> <%: Html.ActionLink("Details", "Details", new { id = item.Product1 })%> </td> this is what im using to list some products from a sql database, each product have a link to a Details page to show more informations about it what Im trying is to only put the product label in that link to let it show something like www.mysite.com\products\battery (not the id) I've imagined this should work, but it throw an The data types text and nvarchar are incompatible in the equal to operator. error and neither (pr => pr.Product1.Equals(id)); works the error is clear and Im asking how should I do to make it work this way ? thanks

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• regarding like query operator

  - by stackoverflowuser

  Hi For the below data (well..there are many more nodes in the team foundation server table which i need to refer to..below is just a sample) Nodes ------------------------ \node1\node2\node3\ \node1\node2\node5\ \node1\node2\node3\node4 I was wondering if i can apply something like (below query does not give the required results) select * from table_a where nodes like '\node1\node2\%\' to get the below data \node1\node2\node3\ \node1\node2\node5\ and something like (below does not give the required results) select * from table_a where nodes like '\node1\node2\%\%\' to get \node1\node2\node3\ \node1\node2\node5\ \node1\node2\node3\node4 Can the above be done with like operator? Pls. suggest. Thanks

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• Does replacing statements by expressions using the C++ comma operator could allow more compiler opti

  - by Gabriel Cuvillier

  The C++ comma operator is used to chain individual expressions, yielding the value of the last executed expression as the result. For example the skeleton code (6 statements, 6 expressions): step1; step2; if (condition) step3; return step4; else return step5; May be rewritten to: (1 statement, 6 expressions) return step1, step2, condition? step3, step4 : step5; I noticed that it is not possible to perform step-by-step debugging of such code, as the expression chain seems to be executed as a whole. Does it means that the compiler is able to perform special optimizations which are not possible with the traditional statement approach (specially if the steps are const or inline)? Note: I'm not talking about the coding style merit of that way of expressing sequence of expressions! Just about the possible optimisations allowed by replacing statements by expressions.

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• Overriding rubies spaceship operator <=>

  - by ericsteen1

  I am trying to override rubies <= (spaceship) operator to sort apples and oranges so that apples come first sorted by weight, and oranges second, sorted by sweetness. Like so: module Fruity attr_accessor :weight, :sweetness def <=>(other) # use Array#<=> to compare the attributes [self.weight, self.sweetness] <=> [other.weight, other.sweetness] end include Comparable end class Apple include Fruity def initialize(w) self.weight = w end end class Orange include Fruity def initialize(s) self.sweetness = s end end fruits = [Apple.new(2),Orange.new(4),Apple.new(6),Orange.new(9),Apple.new(1),Orange.new(22)] p fruits #should work? p fruits.sort But this does not work, can someone tell what I am doing wrong here, or a better way to do this?

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• USing Min/Max with conditional operator

  - by user638501

  Hello All, I am trying to run a query to find max and min values, and then use a conditional operator. however when I try to run the following query, it gives me error - "misuse of aggregate: min()". My query is: SELECT a.prim_id, min(b.new_len*36) as min_new_len, max(b.new_len*36) as max_new_len FROM tb_first a, tb_second b WHERE a.sec_id = b.sec_id AND min_new_len > 1900 AND max_new_len < 75000 GROUP BY a.prim_id ORDER BY avg(b.new_len*36); Any suggestions ?

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• Boolean Not operator in VBScript

  - by Lumi

  Consider the following two conditionals (involving bitwise comparisons) in VBScript: If 1 And 3 Then WScript.Echo "yes" Else WScript.Echo "no" If Not(1 And 3) Then WScript.Echo "yes" Else WScript.Echo "no" Prints first yes, then no, right? cscript not.vbs Wrong! It prints yes twice! Wait a second, the Not operator is supposed to perform logical negation on an expression. The logical negation of true is false, as far as I know. Must I conclude that it doesn't live up to that promise? How and why and what is going on here? What is the rationale, if any?

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• ms-access: missing operator in query expression

  - by every_answer_gets_a_point

  i have this sql statement in access: SELECT * FROM (SELECT [Occurrence Number], [1 0 Preanalytical (Before Testing)], NULL, NULL,NULL FROM [Lab Occurrence Form] WHERE NOT ([1 0 Preanalytical (Before Testing)] IS NULL) UNION SELECT [Occurrence Number], NULL, [2 0 Analytical (Testing Phase)], NULL,NULL FROM [Lab Occurrence Form] WHERE NOT ([2 0 Analytical (Testing Phase)] IS NULL) UNION SELECT [Occurrence Number], NULL, NULL, [3 0 Postanalytical ( After Testing)],NULL FROM [Lab Occurrence Form] WHERE NOT ([3 0 Postanalytical ( After Testing)] IS NULL) UNION SELECT [Occurrence Number], NULL, NULL,NULL [4 0 Other] FROM [Lab Occurrence Form] WHERE NOT ([4 0 Other] IS NULL) ) AS mySubQuery ORDER BY mySubQuery.[Occurrence Number]; everything was fine until i added the last line: SELECT [Occurrence Number], NULL, NULL,NULL [4 0 Other] FROM [Lab Occurrence Form] WHERE NOT ([4 0 Other] IS NULL) i get this error: syntax error (missing operator) in query expression 'NULL [4 0 Other]' anyone have any clues why i am getting this error?

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• Why does std::map operator[] create an object if the key doesn't exist?

  - by n1ck

  Hi, I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there either) but a quick search here doesn't seem to find it so here it is: Why does the std::map operator[] create an object if the key doesn't exist? I don't know but for me this seems counter-intuitive if you compare to most other operator[] (like std::vector) where if you use it you must be sure that the index exists. I'm wondering what's the rationale for implementing this behavior in std::map. Like I said wouldn't it be more intuitive to act more like an index in a vector and crash (well undefined behavior I guess) when accessed with an invalid key? Refining my question after seeing the answers: Ok so far I got a lot of answers saying basically it's cheap so why not or things similar. I totally agree with that but why not use a dedicated function for that (I think one of the comment said that in java there is no operator[] and the function is called put)? My point is why doesn't map operator[] work like a vector? If I use operator[] on an out of range index on a vector I wouldn't like it to insert an element even if it was cheap because that probably mean an error in my code. My point is why isn't it the same thing with map. I mean, for me, using operator[] on a map would mean: i know this key already exist (for whatever reason, i just inserted it, I have redundancy somewhere, whatever). I think it would be more intuitive that way. That said what are the advantage of doing the current behavior with operator[] (and only for that, I agree that a function with the current behavior should be there, just not operator[])? Maybe it give clearer code that way? I don't know. Another answer was that it already existed that way so why not keep it but then, probably when they (the ones before stl) choose to implement it that way they found it provided an advantage or something? So my question is basically: why choose to implement it that way, meaning a somewhat lack of consistency with other operator[]. What benefit do it give? Thanks

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• Analyzing Python Code: Modulus Operator

  - by Bhubhu Hbuhdbus

  I was looking at some code in Python (I know nothing about Python) and I came across this portion: def do_req(body): global host, req data = "" s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect((host, 80)) s.sendall(req % (len(body), body)) tmpdata = s.recv(8192) while len(tmpdata) > 0: data += tmpdata tmpdata = s.recv(8192) s.close() return data This is then called later on with body of huge size, as in over 500,000 bytes. This is sent to an Apache server that has the max request size on the default 8190 bytes. My question is what is happening at the "s.sendall()" part? Obviously the entire body cannot be sent at once and I'm guessing it is reduced by way of the modulus operator. I don't know how it works in Python, though. Can anyone explain? Thanks.

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• Overriding Ruby's spaceship operator <=>

  - by ericsteen1

  I am trying to override Ruby's <= (spaceship) operator to sort apples and oranges so that apples come first sorted by weight, and oranges second, sorted by sweetness. Like so: module Fruity attr_accessor :weight, :sweetness def <=>(other) # use Array#<=> to compare the attributes [self.weight, self.sweetness] <=> [other.weight, other.sweetness] end include Comparable end class Apple include Fruity def initialize(w) self.weight = w end end class Orange include Fruity def initialize(s) self.sweetness = s end end fruits = [Apple.new(2),Orange.new(4),Apple.new(6),Orange.new(9),Apple.new(1),Orange.new(22)] p fruits #should work? p fruits.sort But this does not work, can someone tell what I am doing wrong here, or a better way to do this?

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• C++ vector<T>::iterator operator +

  - by Tom

  Hi, Im holding an iterator that points to an element of a vector, and I would like to compare it to the next element of the vector. Here is what I have Class Point{ public: float x,y; } //Somewhere in my code I do this vector<Point> points = line.getPoints(); foo (points.begin(),points.end()); where foo is: void foo (Vector<Point>::iterator begin,Vector<Point>::iterator end) { std::Vector<Point>::iterator current = begin; for(;current!=end-1;++current) { std::Vector<Point>::iterator next = current + 1; //Compare between current and next. } } I thought that this would work, but current + 1 is not giving me the next element of the vector. I though operator+ was the way to go, but doesnt seem so. Is there a workaround on this? THanks

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• C# == operator in Immediate window behaves differently than at run-time

  - by Damiano

  Try the following in the Immediate window: object a1 = "a"; object a2 = "a"; a1==a2 // outputs false and you'll see that a1 == a2 outputs false. However, at runtime in either a window app or console, you'll get true: object t1 = "a"; object t2 = "a"; MessageBox.Show((t1 == t2).ToString()); // outputs true The runtime behavior is consistent with the definition for the == operator and strings. Does anybody know if this a bug in the Immediate window?

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• Logical xor operator in c++?

  - by RAC

  Is there such a thing? First time I encountered a practical need for it, but I don't see one listed in stroustrup. I intend to write: // Detect when exactly one of A,B is equal to five. return (A==5) ^^ (B==5); But there is no ^^ operator. Can I use bitwise ^ here and get the right answer (regardless of machine representation of true and false)? I never mix & and &&, or | and ||, so I hesitate to do that with ^ and ^^. I'd be more comfortable writing my own "bool XOR(bool,bool)" function instead.

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• Suppress error with @ operator in PHP

  - by Mez

  In your opinion, is it ever valid to use the @ operator to suppress an error/warning in PHP whereas you may be handling the error? If so, in what circumstances would you use this? Code examples are welcome. Edit: Note to repliers. I'm not looking to turn error reporting off, but, for example, common practice is to use @fopen($file); and then check afterwards... but you can get rid of the @ by doing if (file_exists($file)) { fopen($file); } else { die('File not found'); } or similar. I guess the question is - is there anywhere that @ HAS to be used to supress an error, that CANNOT be handled in any other manner?

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• How to replace a codebehind method with an aspx method using ternary operator

  - by user466663

  I have an asp:hyperlink control as part of a gridview template. The code in the aspx page is given below: asp:HyperLink runat="server" ID="lnkEdit" ToolTip="Edit article" NavigateUrl='<%# GetUrl(Eval("ID").ToString(), Eval("CategoryID").ToString()) %' ImageUrl="~/Images/Edit.gif" The NavigateUrl value is obtained from the codebehind method GetUrl(string, string). The code works fine and is as follows: protected string GetUrl(string id, string categoryID) { var CategoryID = string.Empty; if (!String.IsNullOrEmpty(Request.QueryString["CatID"])) { CategoryID = Request.QueryString["CatID"].ToString(); } else if (!String.IsNullOrEmpty(categoryID)) { CategoryID = categoryID; } return "~/TBSArticles/WriteOrEditArticle.aspx?ID=" + id + "&CatID=" + CategoryID; } I want to replace the code behind method by using a ternary operator within the aspx page. I tried something like below, but didn't work: asp:HyperLink runat="server" ID="lnkEdit" ToolTip="Edit article" NavigateUrl='<%# "~/TBSArticles/WriteOrEditArticle.aspx?ID=" + Eval("ID") + "&CatID=" + Eval(this.Request.QueryString["CatID"].ToString()) != ""? this.Request.QueryString["CatID"] : Eval("CategoryID")) %' ImageUrl="~/Images/Edit.gif" Any help will be greatly appreciated. Thanks

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• C++: Why does gcc prefer non-const over const when accessing operator[]?

  - by JonasW

  This question might be more appropriately asked regarding C++ in general, but as I am using gcc on linux that's the context. Consider the following program: #include <iostream> #include <map> #include <string> using namespace std; template <typename TKey, typename TValue> class Dictionary{ public: map<TKey, TValue> internal; TValue & operator[](TKey const & key) { cout << "operator[] with key " << key << " called " << endl; return internal[key]; } TValue const & operator[](TKey const & key) const { cout << "operator[] const with key " << key << " called " << endl; return internal.at(key); } }; int main(int argc, char* argv[]) { Dictionary<string, string> dict; dict["1"] = "one"; cout << "first one: " << dict["1"] << endl; return 0; } When executing the program, the output is: operator[] with key 1 called operator[] with key 1 called first one: one What I would like is to have the compiler choose the operator[]const method instead in the second call. The reason is that without having used dict["1"] before, the call to operator[] causes the internal map to create the data that does not exist, even if the only thing I wanted was to do some debugging output, which of course is a fatal application error. The behaviour I am looking for would be something like the C# index operator which has a get and a set operation and where you could throw an exception if the getter tries to access something that doesn't exist: class MyDictionary<TKey, TVal> { private Dictionary<TKey, TVal> dict = new Dictionary<TKey, TVal>(); public TVal this[TKey idx] { get { if(!dict.ContainsKey(idx)) throw KeyNotFoundException("..."); return dict[idx]; } set { dict[idx] = value; } } } Thus, I wonder why the gcc prefers the non-const call over the const call when non-const access is not required.

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• Why operator= returns reference not const reference

  - by outmind

  The original question is related to overloading operator= and I like to share my findings as it was nontrivial for me to find them. I cannot imagine reasonable example to use (a=b) as lvalue. With the help of IRC and google I've found the next article: http://msdn.microsoft.com/en-us/magazine/cc301415.aspx it provides two examples. (a=b)=c f(T& ); f(a=b) but both a bit not good, as first violate associativity and I believe that it is bad practice. The second one give me the same feeling. Could you provide more good examples why it should be non constant?

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• How does the increment operator (++) work on DateTime in C#

  - by sohtimsso1970

  What happens if you use the increment operator (++) on a DateTime type in C#? For instance, if I did this: DateTime blah = new DateTime(2010, 12, 24); blah++; What does blah become? Does that increment by a tick or a day? Or is that even legal? I don't have a dev environment around, and won't for a few days, or I would just try it and find out. I was too curious to wait so I figured I'd ask the community.

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