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• Intersection of two querysets in django

  - by unagimiyagi

  Hello, I can't do an AND on two querysets. As in, q1 & q2. I get the empty set and I do not know why. I have tested this with the simplest cases. I am using django 1.1.1 I have basically objects like this: item1 name="Joe" color = "blue" item2 name="Jim" color = "blue" color = "white" item3 name="John" color = "red" color = "white" Is there something weird about having a many-to-many relationship or what am I missing? queryset1 = Item.objects.filter(color="blue") this gives (item1, item2) queryset2 = Item.objects.filter(color="white") this gives (item2, item3) queryset1 & queryset2 gives me the empty set [] The OR operator works fine (I'm using "|" ) Why is this so?

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• match at the beginning of any line, including the first

  - by JoelFan

  According the the Perl documentation on regexes: By default, the "^" character is guaranteed to match only the beginning of the string ... Embedded newlines will not be matched by "^" ... You may, however, wish to treat a string as a multi-line buffer, such that the "^" will match after any newline within the string ... you can do this by using the /m modifier on the pattern match operator. The "after any newline" part means that it will only match at the beginning of the 2nd and subsequent lines. What if I want to match at the beginning of any line (1st, 2nd, etc.)?

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• Question regarding built-in type variable is returned from a function

  - by Chan

  Hello, If a local object is returned in a function call, it has to do at least three steps: 1. Copy constructor is called to hold a copy. 2. Destroy local object. 3. A copy is return. For example: x = y + z If x is an integer object. A copy of y + z should be returned, then a new object is created, then assignment operator of x will take this object as parameter. So my question is: Is the same process used for built-in type such as int, double...? If they're not the same, how's it done? Thanks, Chan

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• Init var without copy constructor

  - by Ockonal

  Hello, I have some class(Window) without copy constructor (it's private). I can't understand how to init var of this class in my own class: class MyClass { Window obj; // Hasn't copy constructor public: void init() { obj = Window(/* constructor params */); // [error] obj(/* constructor params */); // [error] } } Error 1: initializing argument 1 of ‘Window::Window(WindowHandle, const sf::WindowSettings&)’ Error 2: ‘NonCopyable& NonCopyable::operator=(const NonCopyable&)’ is private But it works in this way: Window obj(/* constructor params */);

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• Constructing T-SQL WHERE condition at runtime

  - by Nickson

  I would like to implement a search function where a user passes all the arguments to the "WHERE" clause at runtime. For example in query below, SELECT Col1, Col2, Col3, Col4 FROM MyTable WHERE Col2 = John 1.Now what i want is to give the user a dropdownlist of columnns such that the user selects a column to search by at runtime Also instead of precoding Col2 = John, i want the user to choose their own operator at runtime(such as choosing between =, <, <, <, LIKE, IN) i basically want to contruct a query like SELECT Col1, Col2, Col3, Col4 FROM MyTable WHERE (@FieldToSearchBy e.g Col3, @OperatorToUserInSearach e.g LIKE, @ValueToSearch e.g John) I want to pass @FieldToSearchBy, @OperatorToUserInSearach, @ValueToSearch) as user specified parameters at runtime I want to do this with a TableAdpter like in this example http://www.codeproject.com/KB/database/TableAdapter.aspx

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• Deriving streambuf or basic_ostringstream?

  - by Helltone

  Hi, I want to derive a stringstream so that I can use the operator<< to construct a message which will then be thrown. The API would look like: error("some text") << " more text " << 42 << std::endl; This should do a throw "some text more text 42" So what I did is make an errorbuf (inheriting from streambuf) which overloads the 'overflow' method and then create an ostream(&errorbuf). I wonder if I shouldn't instead inherit from basic_ostringstream or something...

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• In Haskell, how can you sort a list of infinite lists of strings?

  - by HaskellNoob

  So basically, if I have a (finite or infinite) list of (finite or infinite) lists of strings, is it possible to sort the list by length first and then by lexicographic order, excluding duplicates? A sample input/output would be: Input: [["a", "b",...], ["a", "aa", "aaa"], ["b", "bb", "bbb",...], ...] Output: ["a", "b", "aa", "bb", "aaa", "bbb", ...] I know that the input list is not a valid haskell expression but suppose that there is an input like that. I tried using merge algorithm but it tends to hang on the inputs that I give it. Can somebody explain and show a decent sorting function that can do this? If there isn't any function like that, can you explain why? In case somebody didn't understand what I meant by the sorting order, I meant that shortest length strings are sorted first AND if one or more strings are of same length then they are sorted using < operator. Thanks!

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• Use case modelling for calculator

  - by kyrogue

  hi, i need help modelling a use case diagram from a topic, it will be in java GUI Design a Calculator that 1.Allow user to key in a legitimate arithmetic statement that involves number, operator +, - and bracket '(' and ')' ; 2.When user press “Calculate” button, display result; 3.Some legitimate statement would be ((3+2)-4+2) (equals 3) and (-2+3)-(3-1) (equals -1); 4.You should NOT use a pre-existing function that just take in the statement as a parameter and returns the result but you should write the logic of parsing every character in your code. 5.Store the last statement and answer so it is displayed when user press the “Last calculation” button. i have designed two use case diagrams using UML on netbeans 6.5.1, one of the use case i am not sure whether is it containing too much use cases etc, while the other is what i think could be too vague for the topic.i hope to get some feedback on whether the use case diagram are appropriate, thanks.

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• what does this C++ line of code mean "sol<?=f((1<<n)-1,i,0)+abs(P[i])*price;"

  - by KItis

  Could anyone help me to understand following line of code. sol I am studying an algorithm written using c++ and it has following operator " following is the error message returned. Hello.cpp: In function ‘int main()’: Hello.cpp:115: error: ‘memset’ was not declared in this scope Hello.cpp:142: error: expected primary-expression before ‘?’ token Hello.cpp:142: error: expected primary-expression before ‘=’ token Hello.cpp:142: error: expected ‘:’ before ‘;’ token Hello.cpp:142: error: expected primary-expression before ‘;’ token may be " Thanks in advance for the time you spent reading this post.

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• Haskell: What is the difference between $ (dollar) and $! (dollar exclamation point)

  - by Jelle Fresen

  Can anybody explain the difference in Haskell between the operators ($) and ($!) (dollar sign vs dollar sign exclamation point)? I haven't seen the use of $! anywhere so far, but while browsing through the Haskell reference on www.zvon.org, I noticed its existence and that it has the exact same definition as $. When trying some simple statements in a Haskell interpreter (ghci), I couldn't find any difference, nor could I find any reference to the operator in the top listed tutorials when googling for haskell tutorial. So, just out of curiosity, what is the difference, if at all?

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• Get a list of documents from Mongo DB

  - by Andrei Neagu

  Hello, I want to do something like this: List<int> fff = new List<int>(); fff.Add(1); fff.Add(2); fff.Add(5); Mongo m = new Mongo(); m.Connect(); var dataBase = m.GetDatabase("database"); var collection = dataBase.GetCollection("coll"); IMongoQuery queryable = collection.AsQueryable(); MongoQueryProvider prov = new MongoQueryProvider(collection); var query = new MongoQuery(prov); var ffppp = from p221 in query where fff.Contains((int)p221["oid"]) select p221; This throws this error : The method 'Contains' could not be converted into a constant. I saw that mongo has an operator $in. Does any one know how can I use it from c#? (http://www.mongodb.org/display/DOCS/Advanced+Queries) Thanks

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• How do you assign a variable with the result of a if..else block?

  - by Pierre Olivier Martel

  I had an argument with a colleague about the best way to assign a variable in an if..else block. His orignal code was : @products = if params[:category] Category.find(params[:category]).products else Product.all end I rewrote it this way : if params[:category] @products = Category.find(params[:category]).products else @products = Product.all end This could also be rewritten with a one-liner using a ternery operator (? :) but let's pretend that product assignment was longer than a 100 character and couldn't fit in one line. Which of the two is clearer to you? The first solution takes a little less space but I thought that declaring a variable and assigning it three lines after can be more error prone. I also like to see my if and else aligned, makes it easier for my brain to parse it!

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• Placement new in gcc

  - by Roman Prikhodchenko

  I need to find a workaround for a bug with placement new in g++. I now it was fixed in gcc-4.3 but I have to support versions 4.2 and 4.1. For example, following code compiles with an error "error: no matching function for call to 'operator new(long unsigned int, void*&)" template<class T, template<typename> class Alloc> inline void* type_ctor() { Alloc<T> a; void* p = a.allocate(1); new(p) T; return p; } ..... type_ctor<A, NewAllocator >();

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• C# implicit conversions

  - by Chris Boden

  Hello, I'm currently working on an application where I need to load data from an SQL database and then assign the retrieved values into the properties of an object. I'm doing this by using reflection since the property names and column names are the same. However, many of the properties are using a custom struct type that is basically a currency wrapper for the decimal type. I have defined an implicit conversion in my struct: public static implicit operator Currency(decimal d) { return new Currency(d); } This works fine when I use it in code. However, when I have this: foreach (PropertyInfo p in props) { p.SetValue(this, table.Rows[0][p.Name], null); } It throws an ArgumentException stating that it cannot convert from System.Decimal to Currency. I'm confused since it works fine in any other circumstance.

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• Is there alternative way to write this query?

  - by Kugel

  I have tables A, B, C, where A represents items which can have zero or more sub-items stored in C. B table only has 2 foreign keys to connect A and C. I have this sql query: select * from A where not exists (select * from B natural join C where B.id = A.id and C.value > 10); Which says: "Give me every item from table A where all sub-items have value less than 10. Is there a way to optimize this? And is there a way to write this not using exists operator?

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• matlab noninteger step indexing

  - by rlbond

  So, I have a vector: k = 1:100; And I want to take 19 elements from it, which are roughly equally-spaced. So I write this: m = k(1:(99/18):end); This works great, except for a tiny problem: Warning: Integer operands are required for colon operator when used as index m = 1 7 12 18 23 29 34 40 45 51 56 62 67 73 78 84 89 95 100 Now, I understand why this comes up, but I'd like to get rid of that warning. Is there a "right" way to do this without a warning?

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• how to get the size of a C global array into an assembly program written for the avr architecture co

  - by johannes

  I have a .c file with the following uint8_t buffer[32] I have a .S file where I want to do the following cpi r29, buffer+sizeof(buffer) The second argument for cpi muste be an imidiate value not a location. But unfortunetly sizeof() is a c operator. Both files, are getting compiled to seperate object files and linked afterwards. If I do avr-objdump -x file.c. Amongst other things, I get the size of the buffer. So it is already available in the object file. How do I access the size of the buffer in my assembly file at compile time?

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• How does sizeof calculate the size of structures

  - by Gearoid Murphy

  I know that a char and an int are calculated as being 8 bytes on 32 bit architectures due to alignment, but I recently came across a situation where a structure with 3 shorts was reported as being 6 bytes by the sizeof operator. Code is as follows: #include <iostream> using namespace std ; struct IntAndChar { int a ; unsigned char b ; }; struct ThreeShorts { unsigned short a ; unsigned short b ; unsigned short c ; }; int main() { cout<<sizeof(IntAndChar)<<endl; // outputs '8' cout<<sizeof(ThreeShorts)<<endl; // outputs '6', I expected this to be '8' return 0 ; } Compiler : g++ (Debian 4.3.2-1.1) 4.3.2. This really puzzles me, why isn't alignment enforced for the structure containing 3 shorts?

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• How to read from a method that returns a filehandle in perl?

  - by Ryan Thompson

  I have an object with a method that returns a filehandle, and I want to read from that handle. The following doesn't work, because the right angle bracket of the method call is interpreted as the closing angle bracket of the input reader: my $input = <$object->get_handle()>; That gets parsed as: my $input = ( < $object- > ) get_handle() >; which is obviously a syntax error. Is there any way I can perform a method call within an angle operator, or do I need to break it into two steps like this? my $handle = $object->get_handle(); my $input = <$handle>;

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• g++ How to get warning on ignoring function return value

  - by ArunSaha

  lint produces some warning like: foo.c XXX Warning 534: Ignoring return value of function bar() From the lint manual 534 Ignoring return value of function 'Symbol' (compare with Location) A function that returns a value is called just for side effects as, for example, in a statement by itself or the left-hand side of a comma operator. Try: (void) function(); to call a function and ignore its return value. See also the fvr, fvo and fdr flags in §5.5 "Flag Options". I want to get this warning, if there exists any, during compilation. Is there any option in gcc/g++ to achieve this? I had turned on -Wall but that apparently did not detect this.

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• std::map default value for build-in type

  - by Qifa Zhao

  Recently, I was confused by the std::map operator[] function. In the MSDN library, it says: "If the argument key value is not found, then it is inserted along with the default value of the data type." I tryed to search much more exactly explanation for this issue. For example here: std::map default value In this page, Michael Anderson said that "the default value is constructed by the default constructor(zero parameter constructor)". Now my quest comes to this:"what the default value for the build-in type?". Was it compiler related? Or is there a standard for this issue by the c++ stardard committee? I did a test on visual studio 2008 for the "int" type, and found the "int" type is construted with the value 0.

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• Does std::multiset guarntee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• Completion block not being called. How to check validity?

  - by HCHogan

  I have this method which takes a block, but that block isn't always called. See the method: - (void)updateWithCompletion:(void (^)(void))completion { [MYObject myMethodWithCompletion:^(NSArray *array, NSError *error) { if (error) { NSLog(@"%s, ERROR not nil", __FUNCTION__); completion(); return; } NSLog(@"%s, calling completion %d", __FUNCTION__, &completion); completion(); NSLog(@"%s, finished completion", __FUNCTION__); }]; } I have some more NSLogs inside completion. Sometimes this program counter just blows right past the call to completion() in the code above. I don't see why this would be as the calling code always passes a literal block of code as input. If you're curious of the output of the line containing the addressof operator, it's always something different, but never 0 or nil. What would cause completion not to be executed?

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• Postgres column casting...

  - by Simon

  I have a query SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = 7 which doesn't work and throws ERROR: operator does not exist: character varying = integer LINE 4: FROM sq_ast WHERE assetid = 7 I can get it to work by doing SELECT assetid, type_code, version, name, short_name, status, languages, charset, force_secure, created, created_userid, updated, updated_userid, published, published_userid, status_changed, status_changed_userid FROM sq_ast WHERE assetid = '7' Please note the quoting of the 7 in the WHERE clause... I am deploying an huge application and I cannot rewrite the core... similarly I don't want to risk changing the type of the column... I'm no Postgres expert... please help... Is there an option for strict casting of columns???

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• Why will this code compile using ifort compiler and not when using gfortran compiler? Help!

  - by CuriousCompiler

  I'm rewriting some code to make a program compile with the gfortran compiler as opposed to ifort compiler I usually use. The code follows: _Subroutine SlideBits (WORD, BITS, ADDR) Implicit None Integer(4) WORD Integer(4) BITS Integer(4) ADDR Integer(4) ADDR1 ADDR1 = 32 - ADDR WORD = (WORD .And. (.Not.ISHFT(1,ADDR1))) .Or. ISHFT(BITS,ADDR1) End_ When I compile the above code using the gfortran compiler, I recieve this error: WORD = (WORD .And. (.Not.ISHFT(1,ADDR1))) .Or. ISHFT(BITS,ADDR1) Error: Operand of .NOT. operator at (1) is INTEGER(4) All three of the variables coming into the subroutine are integers. I've looked around a bit and the gfortran wiki states that the gfortran compiler should be able to handle logical statments being applied to integer values. Several other sites I've visited either quote from the gnu wiki or agree with it. This is the first time I've seen this error as the Intel Fortran compiler (ifort) I normally use compiles cleanly.

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