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• Which are your favorite programming language gadgets?

  - by FerranB

  There are some gadgets/features for programming languages that I like a lot because they save a lot of coding or simply because they are magical or nice. Some of my favorites are: C++ increment/decrement operator: my_array[++c]; C++ assign and sum or substract (...): a += b C# yield return: yield return 1; C# foreach: foreach (MyClass x in MyCollection) PLSQL for loop: for c in (select col1, col2 from mytable) PLSQL pipe row: for i in 1..x loop pipe row(i); end loop; Python Array access operator: a[:1] PLSQL ref cursors. Which are yours?

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• How to efficiently SELECT rows from database table based on selected set of values

  - by Chau Chee Yang

  I have a transaction table of 1 million rows. The table has a field name "Code" to keep customer's ID. There are about 10,000 different customer code. I have an GUI interface allow user to render a report from transaction table. User may select arbitrary number of customers for rendering. I use IN operator first and it works for few customers: SELECT * FROM TRANS_TABLE WHERE CODE IN ('...', '...', '...') I quickly run into problem if I select few thousand customers. There is limitation using IN operator. An alternate way is create a temporary table with only one field of CODE, and inject selected customer codes into the temporary table using INSERT statement. I may then using SELECT A.* FROM TRANS_TABLE A INNER JOIN TEMP B ON (A.CODE=B.CODE) This works nice for huge selection. However, there is performance overhead for temporary table creation, INSERT injection and dropping of temporary table. Do you aware of better solution to handle this situation?

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• How do I use modulus for float/double?

  - by ShrimpCrackers

  I'm creating an RPN calculator for a school project. I'm having trouble with the modulus operator. Since we're using the double data type, modulus won't work on floating point numbers. For example, 0.5 % 0.3 should return 0.2 but I'm getting a division by zero exception. The instruction says to use fmod(). I've looked everywhere for fmod(), including javadocs but I can't find it. I'm starting to think it's a method I'm going to have to create? edit: hmm, strange. I just plugged in those numbers again and it seems to be working fine...but just in case. Do I need to watch out using the mod operator in Java when using floating types? I know something like this can't be done in C++ (I think).

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• Referring to this pointer in a static assert?

  - by Tyson Jacobs

  Is it possible to write a static assert referring to the 'this' pointer? I do not have c++11 available, and BOOST_STATIC_ASSERT doesn't work. struct blah { void func() {BOOST_STATIC_ASSERT(sizeof(*this));} }; Produces: error C2355: 'this' : can only be referenced inside non-static member functions error C2027: use of undefined type 'boost::STATIC_ASSERTION_FAILURE' In MSVC 2008. Motivation: #define CLASS_USES_SMALL_POOL() \ void __small_pool_check() {BOOST_STATIC_ASSERT(sizeof(*this) < SMALL_MALLOC_SIZE;} \ void* operator new(size_t) {return SmallMalloc();} \ void operator delete(void* p) {SmallFree(p);}

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• Constructor or Explicit cast

  - by Felan

  In working with Linq to Sql I create a seperate class to ferry data to a web page. To simplify creating these ferry objects I either use a specialized constructor or an explicit conversion operator. I have two questions. First which approach is better from a readibility perspective? Second while the clr code that is generated appeared to be the same to me, are there situations where one would be treated different than the other by the compiler (in lambda's or such). Example code (DatabaseFoo uses specialized constructor and BusinessFoo uses explicit operator): public class DatabaseFoo { private static int idCounter; // just to help with generating data public int Id { get; set; } public string Name { get; set; } public DatabaseFoo() { Id = idCounter++; Name = string.Format("Test{0}", Id); } public DatabaseFoo(BusinessFoo foo) { this.Id = foo.Id; this.Name = foo.Name; } } public class BusinessFoo { public int Id { get; set; } public string Name { get; set; } public static explicit operator BusinessFoo(DatabaseFoo foo) { return FromDatabaseFoo(foo); } public static BusinessFoo FromDatabaseFoo(DatabaseFoo foo) { return new BusinessFoo {Id = foo.Id, Name = foo.Name}; } } public class Program { static void Main(string[] args) { Console.WriteLine("Creating the initial list of DatabaseFoo"); IEnumerable<DatabaseFoo> dafoos = new List<DatabaseFoo>() { new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo(), new DatabaseFoo()}; foreach(DatabaseFoo dafoo in dafoos) Console.WriteLine(string.Format("{0}\t{1}", dafoo.Id, dafoo.Name)); Console.WriteLine("Casting the list of DatabaseFoo to a list of BusinessFoo"); IEnumerable<BusinessFoo> bufoos = from x in dafoos select (BusinessFoo) x; foreach (BusinessFoo bufoo in bufoos) Console.WriteLine(string.Format("{0}\t{1}", bufoo.Id, bufoo.Name)); Console.WriteLine("Creating a new list of DatabaseFoo by calling the constructor taking BusinessFoo"); IEnumerable<DatabaseFoo> fufoos = from x in bufoos select new DatabaseFoo(x); foreach(DatabaseFoo fufoo in fufoos) Console.WriteLine(string.Format("{0}\t{1}", fufoo.Id, fufoo.Name)); } }

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• REST/ROA Architecture - Send database search/querying/filter/sorting parameters in URL? (>, <, IN, e

  - by DutrowLLC

  I'm building a REST interface to my application using ROA (Resource Oriented Architecture) . I'd like to give the client the ability to specify search parameters in URL. So a client could say "Give me all people who's: "first_name" is equal to "BOB" "age" is greater than "30" sort by "last_name" I was thinking something like: GET /PEOPLE/{query_parameters}/{sort_parameters} ...or perhaps GET /PEOPLE?query=<query_string>&sort=<sort_string> ...but I'm unsure what syntax would be good for specifying in the COLUMN_NAME-OPERATOR-VALUE triplicates. I was thinking perhaps something like: column_name.operator.value So the client could say: GET /PEOPLE?query=first_name.EQUALS.bob&query=age.GREATER_THAN.30&sort=last_name.ASCENDING I really don't want to re-invent the wheel here, are there some accepted ways that this is done? I am using Restlets, I don't know if that makes a difference.

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• How to evaluate a custom math expression in Python

  - by taynaron

  I'm writing a custom dice rolling parser (snicker if you must) in python. Basically, I want to use standard math evaluation but add the 'd' operator: #xdy sum = 0 for each in range(x): sum += randInt(1, y) return sum So that, for example, 1d6+2d6+2d6-72+4d100 = (5)+(1+1)+(6+2)-72+(5+39+38+59) = 84 I was using regex to replace all 'd's with the sum and then using eval, but my regex fell apart when dealing with parentheses on either side. Is there a faster way to go about this than implementing my own recursive parsing? Perhaps adding an operator to eval?

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• Search object array for matching possible multiple values using different comparison operators

  - by Sparkles

  I have a function to search an array of objects for a matching value using the eq operator, like so: sub find { my ( $self, %params ) = @_; my @entries = @{ $self->{_entries} }; if ( $params{filename} ) { @entries = grep { $_->filename eq $params{filename} } @entries; } if ( $params{date} ) { @entries = grep { $_->date eq $params{date} } @entries; } if ( $params{title} ) { @entries = grep { $_->title eq $params{title} } @entries; } .... I wanted to also be able to pass in a qr quoted variable to use in the comparison instead but the only way I can think of separating the comparisons is using an if/else block, like so: if (lc ref($params{whatever}) eq 'regexp') { #use =~ } else { #use eq } Is there a shorter way of doing it? Because of reasons beyond my control I'm using Perl 5.8.8 so I can't use the smart match operator. TIA

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• C# Lambda Problem

  - by Chris Klepeis

  Probably something simple, but as I'm new to lambda expressions, the problem evades me: m => m.contactID == contactID && m.primaryAddress == true && (m.addressTypeID == 2 || m.addressTypeID == 3) I tried to use that lambda expression but I receive an invalid operator. Is there a way to simplify this so that it would work? Edit: The equivolent sql query would be: SELECT * FROM Contact WHERE contactID = 3 AND primaryAddress = 1 AND (addressTypeID = 2 OR addressTypeID = 3) I have a repository function defined like so: public E Single(Expression<Func<E, bool>> where) { return objectSet.Single<E>(where); } I'm passing the lambda expression above into this function. Invalid operator error.

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• What is more interesting or powerful: Curry/Mercury/Lambda-Prolog/your suggestion.

  - by Bubba88

  Hi! I would like to ask you about what formal system could be more interesting to implement from scratch/reverse engineer. I've looked through some existing and rather open (open in the sense of free/open-source) projects of logical/declarative programming systems. I've decided to make up something similar in my free time, or at least to catch the general idea of implementation. It would be great if some of these systems would provide most of the expressive power and conciseness of modern academic investigations in logic and it's relation with computational models. What would you recommend to study at least at the conceptual level? For example, Lambda-Prolog is interesting particularly because it allows for higher order relations, but AFAIK (I might really be mistaken :)) is based on intuitionist logic and therefore lack the excluded-middle principle; that's generally a disatvantage for me.. I would also welcome any suggestions about modern logical programming systems which are less popular but more expressive/powerful. I guess, this question will need refactoring, but thank you in advance! :)

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• How can I have a serializable struct that wraps it's self as an int32 implicitly? in C#?

  - by firoso

  Long story short, I have a struct (see below) that contains exactly one field: private int value; I've also implemented implicit conversion operators: public static implicit operator int(Outlet val) { return val.value; } public static implicit operator Outlet(int val) { return new Outlet(val); } I've implemented all of the following : IComparable, IComparable<Cart>, IComparable<int>, IConvertible, IEquatable<Cart>, IEquatable<int>, IFormattable I'm at a point where I really have no clue why, but whenever I serialize this object, I get no value. For instance, with XmlSerialization: <Outlet /> Also, I'm not solely concerned about XmlSerialization, I'm concerned about ALL serialization (binary for instance) How can I ensure that this serializes properly? NOTE: I did this because mapping an int,int dictionary seemed rather poorly typed to me when explicit objects with validation behavior were desired.

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• What are the common programming mistakes in Python?

  - by Paul McGuire

  I was about to tag the recent question in which the OP accidentally shadowed the builtin operator module with his own local operator.py with the "common-mistakes" tag, and I saw that there are a number of interesting questions posted asking for common mistakes to avoid in Java, Ruby, Scala, Clojure, .Net, jQuery, Haskell, SQL, ColdFusion, and so on, but I didn't see any for Python. For the benefit of Python beginners, can we enumerate the common mistakes that we have all committed at one time or another, in the hopes of maybe steering a newbie or two clear of them? (In homage to "The Princess Bride", I call these the Classic Blunders.) If possible, a little supporting explanation on what the problem is, and the generally accepted resolution/workaround, so that the beginning Pythoner doesn't read your answer and say "ok, that's a mistake, how do I fix it?"

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• Returning references while using shared_ptrs

  - by Goose Bumper

  Suppose I have a rather large class Matrix, and I've overloaded operator== to check for equality like so: bool operator==(Matrix &a, Matrix &b); Of course I'm passing the Matrix objects by reference because they are so large. Now i have a method Matrix::inverse() that returns a new Matrix object. Now I want to use the inverse directly in a comparison, like so: if (a.inverse()==b) { ... }` The problem is, this means the inverse method needs to return a reference to a Matrix object. Two questions: Since I'm just using that reference in this once comparison, is this a memory leak? What happens if the object-to-be-returned in the inverse() method belongs to a boost::shared_ptr? As soon as the method exits, the shared_ptr is destroyed and the object is no longer valid. Is there a way to return a reference to an object that belongs to a shared_ptr?

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• Fully automated SQL Server Restore

  - by hasen j

  I'm not very fluent with SQL Server commands. I need a script to restore a database from a .bak file and move the logical_data and logical_log files to a specific path. I can do: restore filelistonly from disk='D:\backups\my_backup.bak' This will give me a result set with a column LogicalName, next I need to use the logical names from the result set in the restore command: restore database my_db_name from disk='d:\backups\my_backups.bak' with file=1, move 'logical_data_file' to 'd:\data\mydb.mdf', move 'logical_log_file' to 'd:\data\mylog.ldf' How do I capture the logical names from the first result set into variables that can be supplied to the "move" command? I think the solution might be trivial, but I'm pretty new to SQL Server.

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• how to run foreach loop with ternary condition

  - by I Like PHP

  i have two foreach loop to display some data, but i want to use a single foreach on basis of database result. means if there is any row returns from database then forach($first as $fk=>$fv) should execute otherwise foreach($other as $ok) should execute. i m unsing below ternary operator which gives parse error $n=$db->numRows($taskData); // databsse results <?php ($n) ? foreach ($first as $fk=>$fv) : foreach ($other as $ok) { ?> <table><tr><td>......some data...</td></tr></table> <?php } ?> please suggest me how to handle such condition via ternary operator or any other idea. Thanks

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• Little Employee/Shift timetable HELP!!!

  - by DAVID

  Morning Guys, I have the following tables: operator(ope_id, ope_name) ope_shift(ope_id, shift_id, shift_date) shift(shift_id, shift_start, shift_end) here is a better view of the data http://latinunit.net/emp_shift.txt here is the screenshot of a select statement to the tables http://img256.imageshack.us/img256/4013/opeshift.jpg im using this code SELECT OPE_ID, COUNT(OPE_ID) AS Total_shifts from operator_shift group by ope_id; to view the current total shifts per operator and it works, BUT if there was 500 more rows it would count them all aswell, THE QUESTION is, anyone has a better way of making my database work, or how can i tell the system that those rows are a whole month, i remember i friend said something about count then devide by 30 but im not sure, what if the month isnt finished? and you want to show the emp with highest shifts to date

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• Android - modes of connectivity, device identification and device inter-communication?

  - by MalcomTucker

  Can someone explain a couple of very simple concepts to me - I'm interested in mobile devices running android and how they are identified over networks. Some scenarios: Device is connected over WiFi - presumably the device has a standard IP address as with any host and can communicate with any other android host over TCP/IP (assuming it knows the participating device's IP? Device is connected over bluetooth - how are devices identified in this case? Device is connected over mobile operator's network - this is the one I'm interested in and confused by - is there anyway for two or more devices to discover each other and communicate via the mobile operator's network? How does a device communicate with a backend server in this scenario? In other words, how do apps and devices communicate when not connected to a WiFi network? Thanks for any advice..

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• E4X in ActionScript

  - by Brian Genisio

  Hey all, Looking at the E4X implementation in ActionScript, it occurs to me that they had to figure out how to do three things that I am not sure can be done within ActionScript regularly: Properties/Getters prefixed with @: var myAttribute = xmlPerson.@name; Nameless functions for filtering: xmlData.person.(/* predicate */) lambda syntax for predicates: xmlData.person.(@name == "Brian") So here is my question: Are these just one-off capabilities (much like Vector.<>) they put in just for E4X, therefore keeping out of reach for us? Or do we, as ActionScript developers, have access to these features? More specifically, I'd love to get access to the expression tree of that lambda predicate for my own code (not tied to the XML classes in any way). I figured out that this is called the "filter operator"... but I am not sure how to harness it. Not sure I can... since ActionScript does not allow for operator overloading :(

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• Why doesn't C have rotate left/right operators?

  - by icepack

  A bit of a philosophical question, I suppose. Hope it belongs here. C language has the standard set of bit-wise operations, including OR, AND, XOR, SHIFT LEFT/RIGHT, NOT. Anyone has an idea why rotate left/rotate right isn't included in the language? These operators are of the same complexity as other bit-wise operators and normally require a single assembly instruction, like the others. Besides, I can think of a lot of uses for rotate operator, probably not less than, say, xor operator - so it sounds a bit strange to me that they aren't included in C along with the rest. Edit: Please stop suggesting implementations of rotation operators. I know how to do that and it's not what the question about.

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• Aquamacs and IDLWAVE

  - by nicolavianello

  I've just installed the new Aquamacs 2.0 in my Mac Os X 10.6.3 and I'm an happy user of IDLWAVE on Aquamacs for programming in IDL. Unfortunately I run into a problem which I can't understand. I used in my configuration file to put the following (setq idlwave-surround-by-blank t) for the beautiful space around operator. This used to work till Aquamacs 2.0 preview b3 (third beta release) from that on, it stops to work and every time I type an operator (the same for '=' '<' '' etc) I got the following message Debugger entered--Lisp error: (void-variable idlwave-expand-equal) (lambda nil (interactive) (self-insert-command 1) idlwave-expand- equal -1 -1)() call-interactively((lambda nil (interactive) (self-insert-command 1) idlwave-expand-equal -1 -1) nil nil) Any help is welcommed

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• Iterator for second to last element in a list

  - by BSchlinker

  I currently have the following for loop: for(list<string>::iterator jt=it->begin(); jt!=it->end()-1; jt++) I have a list of strings which is in a larger list (list<list<string> >). I want to loop through the contents of the innerlist until I get to the 2nd to last element. This is because I have already processed the contents of the final element, and have no reason to process them again. However, using it->end()-1 is invalid -- I cannot use the - operator here. While I could use the -- operator, this would decrement this final iterator on each cycle. I believe a STL list is a doubly linked list, so from my perspective, it should be possible to do this. Advice? Thanks in advance

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• Copying a Polymorphic object in C++

  - by doron

  I have base-class Base from which is derived Derived1, Derived2 and Derived3. I have constructed an instance for one of the the derived classes which I store as Base* a. I now need to make a deep copy of the object which I will store as Base* b. As far as I know, the normal way of copying a class is to use copy constructors and to overload operator=. However since I don't know whether a is of type Derived1, Derived2 or Derived3, I cannot think of a way of using either the copy constructor or operator=. The only way I can think of to cleanly make this work is to implement something like: class Base { public: virtual Base* Clone() = 0; }; and the implement Clone in in the derived class as in: class Derivedn : public Base { public: Base* Clone() { Derived1* ret = new Derived1; copy all the data members } }; Java tends to use Clone quite a bit is there more of a C++ way of doing this?

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• R: How can I use apply on rows of a data.frame and get out $column_name?

  - by John

  I'm trying to access $a using the following example: df<-data.frame(a=c("x","x","y","y"),b=c(1,2,3,4)) > df a b 1 x 1 2 x 2 3 y 3 4 y 4 test_fun <- function (data.frame_in) { print (data.frame_in[1]) } I can now access $a if I use an index for the first column: apply(df, 1, test_fun) a "x" a "x" a "y" a "y" [1] "x" "x" "y" "y" But I cannot access column $a with the $ notation: error: "$ operator is invalid for atomic vectors" test_fun_2 <- function (data.frame_in) { print (data.frame_in$a) } >apply(df, 1, test_fun_2) Error in data.frame_in$a : $ operator is invalid for atomic vectors Is this not possible?

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• converting string to int in C++

  - by xbonez

  I am trying to convert a string I read in from a file to an int value so I can store it in an integer variable. This is what my code looks like: ifstream sin; sin.open("movie_output.txt"); string line; getline(sin,line); myMovie.setYear(atoi(line)); Over here, setYear is a mutator in the Movie class (myMovie is an object of Movie class) that looks like this: void Movie::setYear(unsigned int year) { year_ = year; } When I run the code, I get the following error: error C2664: 'atoi' : cannot convert parameter 1 from 'std::string' to 'const char *' 1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

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• Silencing GCC warnings when using an "Uncopyable" class

  - by Kazade

  I have several classes that I don't want to be copyable, some of these classes have pointer data members. To make these classes uncopyable I privately inherit the following class template: template <class T> class Uncopyable { protected: Uncopyable() {} virtual ~Uncopyable() {} private: Uncopyable(const Uncopyable &); T & operator=(const T&); }; Which I used like so: class Entity : private Uncopyable<Entity> { } This works fine, however when I compile with -Weffc++ I still get the following warning: class Entity has pointer data members but does not override Entity(const Entity&) or operator=(const Entity&) Why is it still giving me this warning?

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