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  • Boost bind with asio::placeholders::error

    - by Leandro
    Why it doesn't work? --- boost_bind.cc --- #include #include #include void func1 (const int& i) { } void func2 (const ::asio::error_code& e) { } int main () { ::boost::function f1 = ::boost::bind (&func1, 1); // it doesn't work! ::boost::function f2 = ::boost::bind (&func2, ::asio::placeholders::error); return 0; } This is the error: while_true@localhost:~ g++ -lpthread boost_bind.cc -o boost_bind In file included from boost_bind.cc:2: /usr/include/boost/bind.hpp: In member function ‘void boost::_bi::list1::operator()(boost::_bi::type, F&, A&, int) [with F = void (*)(const asio::error_code&), A = boost::_bi::list0, A1 = boost::arg (*)()]’: /usr/include/boost/bind/bind_template.hpp:20: instantiated from ‘typename boost::_bi::result_traits::type boost::_bi::bind_t::operator()() [with R = void, F = void (*)(const asio::error_code&), L = boost::_bi::list1 (*)()]’ /usr/include/boost/function/function_template.hpp:152: instantiated from ‘static void boost::detail::function::void_function_obj_invoker0::invoke(boost::detail::function::function_buffer&) [with FunctionObj = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:904: instantiated from ‘void boost::function0::assign_to(Functor) [with Functor = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:720: instantiated from ‘boost::function0::function0(Functor, typename boost::enable_if_c::type) [with Functor = boost::_bi::bind_t (*)() , R = void]’ /usr/include/boost/function/function_template.hpp:1040: instantiated from ‘boost::function::function(Functor, typename boost::enable_if_c::type) [with Functor = boost::_bi::bind_t (*)() , R = void]’ boost_bind.cc:14: instantiated from here /usr/include/boost/bind.hpp:232: error: no match for ‘operator[]’ in ‘a[boost::_bi::storage1 (*)()::a1_ [with int I = 1]]’ while_true@localhost:~

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  • Has Twisted changed its dependencies?

    - by cdecker
    Hi all, I'm currently working on a Python/Twisted project which is to be distributed and tested on Planetlab. For some reason my code was working on friday and now that I wanted to test a minor change it refuses to work at all: Traceback (most recent call last): File "acn_a4/src/node.py", line 6, in <module> from twisted.internet.protocol import DatagramProtocol File "/usr/lib/python2.5/site-packages/Twisted-10.0.0-py2.5-linux-i686.egg/twisted/__init__.py", line 18, in <module> from twisted.python import compat File "/usr/lib/python2.5/site-packages/Twisted-10.0.0-py2.5-linux-i686.egg/twisted/python/compat.py", line 146, in <module> import operator File "/home/cdecker/dev/acn/acn_a4/src/operator.py", line 7, in <module> File "/home/cdecker/acn_a4/src/node.py", line 6, in <module> from twisted.internet.protocol import DatagramProtocol File "/usr/lib/python2.5/site-packages/Twisted-10.0.0-py2.5-linux-i686.egg/twisted/internet/protocol.py", line 20, in <module> from twisted.python import log, failure, components File "/usr/lib/python2.5/site-packages/Twisted-10.0.0-py2.5-linux-i686.egg/twisted/python/log.py", line 19, in <module> from twisted.python import util, context, reflect File "/usr/lib/python2.5/site-packages/Twisted-10.0.0-py2.5-linux-i686.egg/twisted/python/util.py", line 5, in <module> import os, sys, hmac, errno, new, inspect, warnings File "/usr/lib/python2.5/inspect.py", line 32, in <module> from operator import attrgetter ImportError: cannot import name attrgetter And since I'm pretty new to python I have no idea what could have caused this problem. All suggestions are welcome :-)

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  • How to print a number with a space as thousand separator?

    - by dygi
    I've got a simple class Currency with overloaded operator<<. I don't know how can i separate the number with spaces every 3 digits, so it looks like: "1 234 567 ISK". #include <cstdlib> #include <iostream> using namespace std; class Currency { int val; char curr[4]; public: Currency(int _val, const char * _curr) { val = _val; strcpy(curr, _curr); } friend ostream & operator<< (ostream & out, const Currency & c); }; ostream & operator<< (ostream & out, const Currency & c) { out << c.val<< " " << c.curr; return out; } int main(int argc, char *argv[]) { Currency c(2354123, "ISK"); cout << c; } What interests me, is somehow the easiest solution for this particular situation.

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  • c# Most efficient way to combine two objects

    - by Dested
    I have two objects that can be represented as an int, float, bool, or string. I need to perform an addition on these two objects with the results being the same thing c# would produce as a result. For instance 1+"Foo" would equal the string "1Foo", 2+2.5 would equal the float 5.5, and 3+3 would equal the int 6 . Currently I am using the code below but it seems like incredible overkill. Can anyone simplify or point me to some way to do this efficiently? private object Combine(object o, object o1) { float left = 0; float right = 0; bool isInt = false; string l = null; string r = null; if (o is int) { left = (int)o; isInt = true; } else if (o is float) { left = (float)o; } else if (o is bool) { l = o.ToString(); } else { l = (string)o; } if (o1 is int) { right = (int)o1; } else if (o is float) { right = (float)o1; isInt = false; } else if (o1 is bool) { r = o1.ToString(); isInt = false; } else { r = (string)o1; isInt = false; } object rr; if (l == null) { if (r == null) { rr = left + right; } else { rr = left + r; } } else { if (r == null) { rr = l + right; } else { rr = l + r; } } if (isInt) { return Convert.ToInt32(rr); } return rr; }

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  • video calling (center)

    - by rrejc
    We are starting to develop a new application and I'm searching for information/tips/guides on application architecture. Application should: read the data from an external (USB) device send the data to the remote server (through internet) receive the data from the remote server perform a video call with to the calling (support) center receive a video call call from the calling (support) center support touch screens In addition: some of the data should also be visible through the web page. So I was thinking about: On the server side: use the database (probably MS SQL) use ORM (nHibernate) to map the data from the DB to the domain objects create a layer with business logic in C# create a web (WCF) services (for client application) create an asp.net mvc application (for item 7.) to enable data view through the browser On the client side I would use WPF 4 application which will communicate with external device and the wcf services on the server. So far so good. Now the problem begins. I have no idea how to create a video call (outgoing or incoming) part of the application. I believe that there is no problem to communicate with microphone, speaker, camera with WPF/C#. But how to communicate with the call center? What protocol and encoding should be used? I think that I will need to create some kind of server which will: have a list of operators in the calling center and track which operator is occupied and which operator is free have a list of connected end users receive incoming calls from end users and delegate call to free operator delegate calls from calling center to the end user Any info, link, anything on where to start would be much appreciated. Many thanks!

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  • Coredump in Multithreading Application in RHEL-5

    - by Chinnu
    I am working on multi-threading application it is dumping frequently.I could not able to analyaze the core.The core is showing like this Core was generated by 'thread-process'. Program terminated with signal 6, Aborted. #0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 (gdb) where #0 0x00000038f4e30045 in raise () from /lib64/libc.so.6 #1 0x00000038f4e31ae0 in abort () from /lib64/libc.so.6 #2 0x00000038f4e681bb in __libc_message () from /lib64/libc.so.6 #3 0x00000038f4e72b96 in free () from /lib64/libc.so.6 #4 0x000000000046a137 in std::string::substr () #5 0x000000000042c549 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #6 0x000000000042cc1d in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #7 0x000000000046b069 in std::string::substr () #8 0x000000000046c866 in std::string::substr () #9 0x0000000000431062 in std::operator<< <char, std::char_traits<char>, std::allocator<char> > () #10 0x00000038f5a062e7 in start_thread () from /lib64/libpthread.so.0 #11 0x00000038f4ece3bd in clone () from /lib64/libc.so.6

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  • Most efficient way to combine two objects in C#

    - by Dested
    I have two objects that can be represented as an int, float, bool, or string. I need to perform an addition on these two objects with the results being the same thing c# would produce as a result. For instance 1+"Foo" would equal the string "1Foo", 2+2.5 would equal the float 5.5, and 3+3 would equal the int 6 . Currently I am using the code below but it seems like incredible overkill. Can anyone simplify or point me to some way to do this efficiently? private object Combine(object o, object o1) { float left = 0; float right = 0; bool isInt = false; string l = null; string r = null; if (o is int) { left = (int)o; isInt = true; } else if (o is float) { left = (float)o; } else if (o is bool) { l = o.ToString(); } else { l = (string)o; } if (o1 is int) { right = (int)o1; } else if (o is float) { right = (float)o1; isInt = false; } else if (o1 is bool) { r = o1.ToString(); isInt = false; } else { r = (string)o1; isInt = false; } object rr; if (l == null) { if (r == null) { rr = left + right; } else { rr = left + r; } } else { if (r == null) { rr = l + right; } else { rr = l + r; } } if (isInt) { return Convert.ToInt32(rr); } return rr; }

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  • rails: has_many :through validation?

    - by ramonrails
    Rails 2.1.0 (Cannot upgrade for now due to several constraints) I am trying to achieve this. Any hints? A project has many users through join model A user has many projects through join model Admin class inherits User class. It also has some Admin specific stuff. Admin like inheritance for Supervisor and Operator Project has one Admin, One supervisor and many operators. Now I want to 1. submit data for project, admin, supervisor and operator in a single project form 2. validate all and show errors on the project form. Project has_many :projects_users ; has_many :users, :through => :projects_users User has_many :projects_users ; has_many :projects, :through => :projects_users ProjectsUser = :id integer, :user_id :integer, :project_id :integer, :user_type :string ProjectUser belongs_to :project, belongs_to :user Admin < User # User has 'type:string' column for STI Supervisor < User Operator < User Is the approach correct? Any and all suggestions are welcome.

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  • How to pass multiple different records (not class due to delphi limitations) to a function?

    - by mingo
    Hi to all. I have a number of records I cannot convert to classes due to Delphi limitation (all of them uses class operators to implement comparisons). But I have to pass to store them in a class not knowing which record type I'm using. Something like this: type R1 = record begin x :Mytype; class operator Equal(a,b:R1) end; type R2 = record begin y :Mytype; class operator Equal(a,b:R2) end; type Rn = record begin z :Mytype; class operator Equal(a,b:Rn) end; type TC = class begin x : TObject; y : Mytype; function payload (n:TObject) end; function TC.payload(n:TObject) begin x := n; end; program: c : TC; x : R1; y : R2; ... c := TC.Create(): n:=TOBject(x); c.payload(n); Now, Delphi do not accept typecast from record to TObject, and I cannot make them classes due to Delphi limitation. Anyone knows a way to pass different records to a function and recognize their type when needed, as we do with class: if x is TMyClass then TMyClass(x) ... ???

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  • function objects versus function pointers

    - by kumar_m_kiran
    Hi All, I have two questions related to function objects and function pointers, Question : 1 When I read the different uses sort algorithm of STL, I see that the third parameter can be a function objects, below is an example class State { public: //... int population() const; float aveTempF() const; //... }; struct PopLess : public std::binary_function<State,State,bool> { bool operator ()( const State &a, const State &b ) const { return popLess( a, b ); } }; sort( union, union+50, PopLess() ); Question : Now, How does the statement, sort(union, union+50,PopLess()) work? PopLess() must be resolved into something like PopLess tempObject.operator() which would be same as executing the operator () function on a temporary object. I see this as, passing the return value of overloaded operation i.e bool (as in my example) to sort algorithm. So then, How does sort function resolve the third parameter in this case? Question : 2 Question Do we derive any particular advantage of using function objects versus function pointer? If we use below function pointer will it derive any disavantage? inline bool popLess( const State &a, const State &b ) { return a.population() < b.population(); } std::sort( union, union+50, popLess ); // sort by population PS : Both the above references(including example) are from book "C++ Common Knowledge: Essential Intermediate Programming" by "Stephen C. Dewhurst". I was unable to decode the topic content, thus have posted for help. Thanks in advance for your help.

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  • How `is_base_of` works?

    - by Alexey Malistov
    Why the following code works? typedef char (&yes)[1]; typedef char (&no)[2]; template <typename B, typename D> struct Host { operator B*() const; operator D*(); }; template <typename B, typename D> struct is_base_of { template <typename T> static yes check(D*, T); static no check(B*, int); static const bool value = sizeof(check(Host<B,D>(), int())) == sizeof(yes); }; //Test sample class Base {}; class Derived : private Base {}; //Exspression is true. int test[is_base_of<Base,Derived>::value && !is_base_of<Derived,Base>::value]; Note that B is private base. Note that operator B*() is const. How does this work? Why this works? Why static yes check(D*, T); is better than static yes check(B*, int); ?

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  • Does this language feature already exists?

    - by Pindatjuh
    I'm currently developing a new language for programming in a continuous environment (compare it to electrical engineering), and I've got some ideas on a certain language construction. Let me explain the feature by explanation and then by definition; x = a | b; Where x is a variable and a and b are other variables (or static values). if(x == a) { // all references to "x" are essentially references to "a". } if(x == b) { // same but with "b" } if(x != a) { // ... } if(x == a | b) { // guaranteed that "x" is '"a" | "b"'; interacting with "x" // will interact with both "a" and "b". } // etc. In the above, all code-blocks are executed, but the "scope" changes in each block how x is interpreted. In the first block, x is guaranteed to be a: thus interacting with x inside that block will interact on a. The second and the third code-block are only equal in this situation (because not b only remains a). The last block guarantees that x is at least a or b. Further more; | is not the "bitwise or operator", but I've called it the "and/or"-operator. It's definition is: "|" = "and" | "or" (On my blog, http://cplang.wordpress.com/2009/12/19/binop-and-or/, is more (mathematical) background information on this operator. It's loosely based on sets.) I do not know if this construction already exists, so that's my question: does this language feature already exists?

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  • ArrayList.Sort should be a stable sort with an IComparer but is not?

    - by Kaleb Pederson
    A stable sort is a sort that maintains the relative ordering of elements with the same value. The docs on ArrayList.Sort say that when an IComparer is provided the sort is stable: If comparer is set to null, this method performs a comparison sort (also called an unstable sort); that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal. To perform a stable sort, you must implement a custom IComparer interface. Unless I'm missing something, the following testcase shows that ArrayList.Sort is not using a stable sort: internal class DisplayOrdered { public int ID { get; set; } public int DisplayOrder { get; set; } public override string ToString() { return string.Format("ID: {0}, DisplayOrder: {1}", ID, DisplayOrder); } } internal class DisplayOrderedComparer : IComparer { public int Compare(object x, object y) { return ((DisplayOrdered)x).DisplayOrder - ((DisplayOrdered)y).DisplayOrder; } } [TestFixture] public class ArrayListStableSortTest { [Test] public void TestWeblinkCallArrayListIsSortedUsingStableSort() { var call1 = new DisplayOrdered {ID = 1, DisplayOrder = 0}; var call2 = new DisplayOrdered {ID = 2, DisplayOrder = 0}; var call3 = new DisplayOrdered {ID = 3, DisplayOrder = 2}; var list = new ArrayList {call1, call2, call3}; list.Sort(new DisplayOrderedComparer()); // expected order (by ID): 1, 2, 3 (because the DisplayOrder // is equal for ID's 1 and 2, their ordering should be // maintained for a stable sort.) Assert.AreEqual(call1, list[0]); // Actual: ID=2 ** FAILS Assert.AreEqual(call2, list[1]); // Actual: ID=1 Assert.AreEqual(call3, list[2]); // Actual: ID=3 } } Am I missing something? If not, would this be a documentation bug or a library bug? Apparently using an OrderBy in Linq gives a stable sort.

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  • Using javascript and php together

    - by EmmyS
    I have a PHP form that needs some very simple validation on submit. I'd rather do the validation client-side, as there's quite a bit of server-side validation that happens to deal with writing form values to a database. So I just want to call a javascript function onsubmit to compare values in two password fields. This is what I've got: function validate(form){ var password = form.password.value; var password2 = form.password2.value; alert("password:"+password+" password2:" + password2); if (password != password2) { alert("not equal"); document.getElementByID("passwordError").style.display="inline"; return false; } alert("equal"); return true; } The idea being that a default-hidden div containing an error message would be displayed if the two passwords don't match. The alerts are just to display the values of password and password2, and then again to indicate whether they match or not (will not be used in production code). I'm using an input type=submit button, and calling the function in the form tag: <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" onsubmit="return validate(this);"> Everything is alerting as expected when entering non-matching values. I would have hoped (and assumed, based on past use) that if the function returned false, the actual submit would not occur. And yet, it is. I'm testing by entering non-matching values in the password fields, and the alerts clearly show me the values and the not equal result, but the actual form action is still occurring and it's trying to write to my database. I'm pretty new at PHP; is there something about it that will not let me combine with javascript this way? Would it be better to use an input type=button and include submit() in the function itself if it returns true?

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  • mysql query help, take total sum from a table, and based on discount value on another table calcula

    - by vegatron
    hi I have a table called invoices: CREATE TABLE IF NOT EXISTS `si_invoices` ( `id` int(10) NOT NULL AUTO_INCREMENT, `biller_id` int(10) NOT NULL DEFAULT '0', `customer_id` int(10) NOT NULL DEFAULT '0', `type_id` int(10) NOT NULL DEFAULT '0', `inv_tax_id` int(10) NOT NULL, `date` date NOT NULL DEFAULT '0000-00-00', `unreg_customer` tinyint(1) NOT NULL DEFAULT '0', `discount` decimal(10,2) NOT NULL DEFAULT '0.00', `discount_type` tinyint(1) NOT NULL DEFAULT '0', PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=20 ; each invoice has items that are stored in invoice_items table : CREATE TABLE IF NOT EXISTS `si_invoice_items` ( `id` int(10) NOT NULL AUTO_INCREMENT, `invoice_id` int(10) NOT NULL DEFAULT '0', `quantity` int(10) unsigned NOT NULL DEFAULT '0', `product_id` int(10) DEFAULT '0', `warehouse_id` int(10) NOT NULL, `unit_price` decimal(25,2) DEFAULT '0.00', `total` decimal(25,2) DEFAULT '0.00', `description` text, PRIMARY KEY (`id`), KEY `invoice_id` (`invoice_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=56 ; and tax table CREATE TABLE IF NOT EXISTS `si_tax` ( `tax_id` int(11) NOT NULL AUTO_INCREMENT, `tax_description` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL, `tax_percentage` decimal(25,6) DEFAULT '0.000000', `type` varchar(1) COLLATE utf8_unicode_ci DEFAULT NULL, `tax_enabled` varchar(1) COLLATE utf8_unicode_ci NOT NULL DEFAULT '1', PRIMARY KEY (`tax_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=5 ; here is what I want to do step 1: get the sum_total of the invoice Items for a speciefic invoice step 2: calculate the discount, in the invoice table I have a discount_type field : if its equal to 0 , then there will be no discount if its equal to 1 , the discount value will be stored in the discount field if its equal to 2 , the discount is a percentage of sum_total step 3: calculate the taxes based on inv_tax_id based on the tax id , I will look in the tax table , get the tax_percentage and multiply it by the (sum_total - discount) in short here is the equation $gross_total = $sum_total - $disount + taxes

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  • How might I wrap the FindXFile-style APIs to the STL-style Iterator Pattern in C++?

    - by BillyONeal
    Hello everyone :) I'm working on wrapping up the ugly innards of the FindFirstFile/FindNextFile loop (though my question applies to other similar APIs, such as RegEnumKeyEx or RegEnumValue, etc.) inside iterators that work in a manner similar to the Standard Template Library's istream_iterators. I have two problems here. The first is with the termination condition of most "foreach" style loops. STL style iterators typically use operator!= inside the exit condition of the for, i.e. std::vector<int> test; for(std::vector<int>::iterator it = test.begin(); it != test.end(); it++) { //Do stuff } My problem is I'm unsure how to implement operator!= with such a directory enumeration, because I do not know when the enumeration is complete until I've actually finished with it. I have sort of a hack together solution in place now that enumerates the entire directory at once, where each iterator simply tracks a reference counted vector, but this seems like a kludge which can be done a better way. The second problem I have is that there are multiple pieces of data returned by the FindXFile APIs. For that reason, there's no obvious way to overload operator* as required for iterator semantics. When I overload that item, do I return the file name? The size? The modified date? How might I convey the multiple pieces of data to which such an iterator must refer to later in an ideomatic way? I've tried ripping off the C# style MoveNext design but I'm concerned about not following the standard idioms here. class SomeIterator { public: bool next(); //Advances the iterator and returns true if successful, false if the iterator is at the end. std::wstring fileName() const; //other kinds of data.... }; EDIT: And the caller would look like: SomeIterator x = ??; //Construct somehow while(x.next()) { //Do stuff } Thanks! Billy3

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  • MySQL SELECT combining 3 SELECTs INTO 1

    - by Martin Tóth
    Consider following tables in MySQL database: entries: creator_id INT entry TEXT is_expired BOOL other: creator_id INT entry TEXT userdata: creator_id INT name VARCHAR etc... In entries and other, there can be multiple entries by 1 creator. userdata table is read only for me (placed in other database). I'd like to achieve a following SELECT result: +------------+---------+---------+-------+ | creator_id | entries | expired | other | +------------+---------+---------+-------+ | 10951 | 59 | 55 | 39 | | 70887 | 41 | 34 | 108 | | 88309 | 38 | 20 | 102 | | 94732 | 0 | 0 | 86 | ... where entries is equal to SELECT COUNT(entry) FROM entries GROUP BY creator_id, expired is equal to SELECT COUNT(entry) FROM entries WHERE is_expired = 0 GROUP BY creator_id and other is equal to SELECT COUNT(entry) FROM other GROUP BY creator_id. I need this structure because after doing this SELECT, I need to look for user data in the "userdata" table, which I planned to do with INNER JOIN and select desired columns. I solved this problem with selecting "NULL" into column which does not apply for given SELECT: SELECT creator_id, COUNT(any_entry) as entries, COUNT(expired_entry) as expired, COUNT(other_entry) as other FROM ( SELECT creator_id, entry AS any_entry, NULL AS expired_entry, NULL AS other_enry FROM entries UNION SELECT creator_id, NULL AS any_entry, entry AS expired_entry, NULL AS other_enry FROM entries WHERE is_expired = 1 UNION SELECT creator_id, NULL AS any_entry, NULL AS expired_entry, entry AS other_enry FROM other ) AS tTemp GROUP BY creator_id ORDER BY entries DESC, expired DESC, other DESC ; I've left out the INNER JOIN and selecting other columns from userdata table on purpose (my question being about combining 3 SELECTs into 1). Is my idea valid? = Am I trying to use the right "construction" for this? Are these kind of SELECTs possible without creating an "empty" column? (some kind of JOIN) Should I do it "outside the DB": make 3 SELECTs, make some order in it (let's say python lists/dicts) and then do the additional SELECTs for userdata? Solution for a similar question does not return rows where entries and expired are 0. Thank you for your time.

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  • What noncluster index would be better to create on SQL Server?

    - by Junior Mayhé
    Here I am studying nonclustered indexes on SQL Server Management Studio. I've created a table with more than 1 million records. This table has a primary key. SELECT CustomerName FROM Customers Which leads the execution plan to show me: I/O cost = 3.45646 Operator cost = 4.57715 For the first attempt to improve performance, I've created a nonclustered index for this table: CREATE NONCLUSTERED INDEX [IX_CustomerID_CustomerName] ON [dbo].[Customers] ( [CustomerId] ASC, [CustomerName] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this first try, I've executed the select statement and the execution plan shows me: I/O cost = 2.79942 Operator cost = 3.92001 Now the second try, I've deleted this nonclustered index in order to create a new one. CREATE NONCLUSTERED INDEX [IX_CategoryName] ON [dbo].[Categories] ( [CategoryId] ASC ) INCLUDE ( [CategoryName]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this second try, I've executed the select statement and the execution plan shows me the same result: I/O cost = 2.79942 Operator cost = 3.92001 Am I doing something wrong or this is expected? Shall I use the first nonclustered index with two fields, or the second nonclustered with one field (CategoryID) including the second field (CategoryName)?

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  • Arduino variable going blank after the first pass

    - by user541597
    I have an Arduino sketch that takes a timet and when that timet is equal to the current time it sets the new timet to timet + 2. For example: char* convert(char* x, String y) { int hour; int minute; sscanf(x, "%d:%d", &hour, &minute); char buf[6]; if (y == "6") { if (hour > 17) { hour = (hour+6)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 18) { //hour = hour + 6; minute = (minute + 2); snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "12") { if (hour > 11) { hour = (hour+12)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } else if (hour < 12) { hour = hour + 12; snprintf(buf, 10, "%d:%d", hour, minute); } } if (y == "24") { hour = (hour+24)%24; snprintf(buf, 10, "%d:%d", hour, minute ); } return buf; } The sketch starts for example at 1:00am. timet is set to 1:02, at system time 1:02 timet is equal to the system time. My loops looks like this: if (timet == currenttime) { timet = convert(timet) } Whenever I check the value of timet it should equal 1:04, however I get the correct value at the first run after the execution of convert, however every time after that my timet value is blank. I tried changing the code instead of using the if loop. I only run the convert function when I send for example t through the serial monitor. This works fine and outputs the correct timet after the execution of the convert function, So I figured the problem is in the if loop... Any ideas?

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  • Link error for user defined class type template parameter

    - by isurulucky
    Hi, I implemented a Simple STL map in C++. Factored out the comparison as a type as I was instructed to, then implemented the comparison as shown below: template <typename T> int KeyCompare<T>::operator () (T tKey1, T tKey2) { if(tKey1 < tKey2) return -1; else if(tKey1 > tKey2) return 1; else return 0; } here, tKey1 and tKet2 are the two keys I'm comparing. This worked well for all the basic data types and string. I added a template specialization to compare keys of a user defined type named Test and added a specialization as follows: int KeyCompare<Test>::operator () (Test tKey1, Test tKey2) { if(tKey1.a < tKey2.a) return -1; else if(tKey1.a > tKey2.a) return 1; else return 0; } when I run this, I get a linking error saying SimpleMap.obj : error LNK2005: "public: int __thiscall KeyCompare::operator()(class Test,class Test)" (??R?$KeyCompare@VTest@@@@QAEHVTest@@0@Z) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::~KeyCompare(void)" (??1?$KeyCompare@VTest@@@@QAE@XZ) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::KeyCompare(void)" (??0?$KeyCompare@VTester@@@@QAE@XZ) already defined in MapTest.obj MapTest.cpp is the test harness class in which I wrote the test case. I have used include guards as well, to stop multiple inclusions. Any idea what the matter is?? Thank you very much!!

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  • How to use boost::fusion::transform on heterogeneous containers?

    - by Kyle
    Boost.org's example given for fusion::transform is as follows: struct triple { typedef int result_type; int operator()(int t) const { return t * 3; }; }; // ... assert(transform(make_vector(1,2,3), triple()) == make_vector(3,6,9)); Yet I'm not "getting it." The vector in their example contains elements all of the same type, but a major point of using fusion is containers of heterogeneous types. What if they had used make_vector(1, 'a', "howdy") instead? int operator()(int t) would need to become template<typename T> T& operator()(T& const t) But how would I write the result_type? template<typename T> typedef T& result_type certainly isn't valid syntax, and it wouldn't make sense even if it was, because it's not tied to the function.

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  • algorithm - How to sort a 0/1 array with 2n/3 comparisons?

    - by Jackson Tale
    In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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  • URL equals and checking Internet access

    - by James P.
    On http://java.sun.com/j2se/1.5.0/docs/api/java/net/URL.html it states that: Compares this URL for equality with another object. If the given object is not a URL then this method immediately returns false. Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file. Two hosts are considered equivalent if both host names can be resolved into the same IP addresses; else if either host name can't be resolved, the host names must be equal without regard to case; or both host names equal to null. Since hosts comparison requires name resolution, this operation is a blocking operation. Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP. According to this, equals will only work if name resolution is possible. Since I can't be sure that a computer has internet access at a given time, should I just use Strings to store addresses instead? Also, how do I go about testing if access is available when requested?

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  • C++ Implicit Conversion Operators

    - by Imbue
    I'm trying to find a nice inheritance solution in C++. I have a Rectangle class and a Square class. The Square class can't publicly inherit from Rectangle, because it cannot completely fulfill the rectangle's requirements. For example, a Rectangle can have it's width and height each set separately, and this of course is impossible with a Square. So, my dilemma. Square obviously will share a lot of code with Rectangle; they are quite similar. For examlpe, if I have a function like: bool IsPointInRectangle(const Rectangle& rect); it should work for a square too. In fact, I have a ton of such functions. So in making my Square class, I figured I would use private inheritance with a publicly accessible Rectangle conversion operator. So my square class looks like: class Square : private Rectangle { public: operator const Rectangle&() const; }; However, when I try to pass a Square to the IsPointInRectangle function, my compiler just complains that "Rectangle is an inaccessible base" in that context. I expect it to notice the Rectangle operator and use that instead. Is what I'm trying to do even possible? If this can't work I'm probably going to refactor part of Rectangle into MutableRectangle class. Thanks.

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  • template warnings and error help, (gcc)

    - by sil3nt
    Hi there, I'm working on an container class template (for int,bool,strings etc), and I've been stuck with this error cont.h:56: error: expected initializer before '&' token for this section template <typename T> const Container & Container<T>::operator=(const Container<T> & rightCont){ what exactly have I done wrong there?. Also not sure what this warning message means. cont.h:13: warning: friend declaration `bool operator==(const Container<T>&, const Container<T>&)' declares a non-template function cont.h:13: warning: (if this is not what you intended, make sure the function template has already been declared and add <> after the function name here) -Wno-non-template-friend disables this warning at this position template <typename T> class Container{ friend bool operator==(const Container<T> &rhs,const Container<T> &lhs); public:

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