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  • Rails: three most recent comments with unique users

    - by Dennis Collective
    what would I put in the named scope :by_unique_users so that I can do Comment.recent.by_unique_users.limit(3), and only get one comment per user? class User has_many :comments end class Comment belongs_to :user named_scope :recent, :order => 'comments.created_at DESC' named_scope :limit, lambda { |limit| {:limit => limit}} named_scope :by_unique_users end on sqlite named_scope :by_unique_user, :group = "user_id" works, but makes it freak out on postgres, which is deployed on production PGError: ERROR: column "comments.id" must appear in the GROUP BY clause or be used in an aggregate function

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  • C/C++ packing signed char into int

    - by aaa
    hello I have need to pack four signed bytes into 32-bit integral type. this is what I came up to: int byte(char c) { return (unsigned char)c; } int pack(char c0, char c1, ...) { return byte(c0) | byte(c1) << 8 | ...; } is this a good solution? Is it portable? is there a ready-made solution, perhaps boost? Thanks

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  • C/C++ include file order/best practices

    - by aaa
    Hello. Is there recommended order in which include files should be specified? For example, the system files, STL, Boost, go before of after local include files? is there a particular reason to choose one or another? Thanks

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  • Best practices for caching results of JSP pages?

    - by Spines
    My application has an MVC structure. How should I structure my application to allow for maximum caching? Is it sufficient to only cache the model objects that are passed to the JSP views? Or will there be a significant performance boost from caching the results of the rendering of the JSP views too?

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  • PySide Qt4 widget exchange in a hboxlayout

    - by viraptor
    I'd like to exchange a widget inside a QHBoxLayout. This code seems to work, but as soon as I do the actual app._exec(), the code crashes with terminate called after throwing an instance of 'boost::python::error_already_set'. Is there any way to get the actual error message? (or to resolve this problem) gaParent = gameArea.parent().layout() gaParent.removeWidget(gameArea) gameArea = DrawingScreen() gameArea.setObjectName("gameArea") gaParent.insertWidget(0, gameArea)

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  • C++: compute a number's complement and its number of possible mismatches

    - by Eagle
    I got a bit stuck with my algorithm and I need some help to solve my problem. I think an example would explain better my problem. Assuming: d = 4 (maximum number of allowed bits in a number, 2^4-1=15). m_max = 1 (maximum number of allowed bits mismatches). kappa = (maximum number of elements to find for a given d and m, where m in m_max) The main idea is for a given number, x, to compute its complement number (in binary base) and all the possible combinations for up to m_max mismatches from x complement's number. Now the program start to scan from i = 0 till 15. for i = 0 and m = 0, kappa = \binom{d}{0} = 1 (this called a perfect match) possible combinations in bits, is only 1111 (for 0: 0000). for i = 0 and m = 1, kappa = \binom{d}{1} = 4 (one mismatch) possible combinations in bits are: 1000, 0100, 0010 and 0001 My problem was to generalize it to general d and m. I wrote the following code: #include <stdlib.h> #include <iomanip> #include <boost/math/special_functions/binomial.hpp> #include <iostream> #include <stdint.h> #include <vector> namespace vec { typedef std::vector<unsigned int> uint_1d_vec_t; } int main( int argc, char* argv[] ) { int counter, d, m; unsigned num_combination, bits_mask, bit_mask, max_num_mismatch; uint_1d_vec_t kappa; d = 4; m = 2; bits_mask = 2^num_bits - 1; for ( unsigned i = 0 ; i < num_elemets ; i++ ) { counter = 0; for ( unsigned m = 0 ; m < max_num_mismatch ; m++ ) { // maximum number of allowed combinations num_combination = boost::math::binomial_coefficient<double>( static_cast<unsigned>( d ), static_cast<unsigned>(m) ); kappa.push_back( num_combination ); for ( unsigned j = 0 ; j < kappa.at(m) ; j++ ) { if ( m == 0 ) v[i][counter++] = i^bits_mask; // M_0 else { bit_mask = 1 << ( num_bits - j ); v[i][counter++] = v[i][0] ^ bits_mask } } } } return 0; } I got stuck in the line v[i][counter++] = v[i][0] ^ bits_mask since I was unable to generalize my algorithm to m_max1, since I needed for m_max mismatches m_max loops and in my original problem, m is unknown until runtime.

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  • Getting started with nbehave

    - by dotnetdev
    Hi, I am looking at using BDD, however, when evaluating the stories/conditions I write (using nBehave), how do I check if the story passes? Do I write another library with test methods? For example, if I want to test a site for having a link called "About", do I write a method which can check this and then another method in another class library which can call the method to check the link via lambda syntax and add the relevant test and bdd attributes? Thanks

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  • Area of a irregular shape

    - by Naveen
    I have set of points which lies on the image. These set of points form a irregular closed shape. I need to find the area of this shape. Does any body which is the normal algorithm used for calculating the area ? Or is there any support available in libraries such as boost? I am using C++.

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  • Code hot swapping in Erlang

    - by Roger Alsing
    I recently saw a video about Erlang on InfoQ, In that video one of the creators presented how to replace the behavior of a message loop. He was simply sending a message containing a lambda of the new version of the message loop code, which then was invoked instead of calling the old loop again. Is that code hot swapping in Erlang reffers to? Or is that some other more native feature?

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  • pure as3 benefits to compiling with flex4 instead of flex3?

    - by jedierikb
    If I have a pure as3 project that I have been compiling with flex3 from mxmlc, is there any reason to switch to using the mxmlc with flex4? I can use all of the flash 10 language features like Vector, 3D, etc., so that is not a reason to switch (or is there something I can't do?). But maybe there is a performance boost? Or is the exact same compiling tool and the flex code base is the only difference?

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  • C++ simple logging class with UTF-8 output [code example]

    - by Andrew
    Hello everyone, I was working on one of my academic projects and for the first time I needed pure C++ without GUI. After googling for a while, I did not find any simple and easy to use implementation for logging and created my own. This is a simple implementation with iostreams that logs messages to screen and to the file simultaneously. I was thinking of using templates but then I realized that I do not expect any changes and removed that. It is modified std::wostream with two added modifiers: 1. TimeStamp - prints time-stamp 2. LogMode(LogModes) - switches output: file only, screen only, file+screen. *Boost::utf8_codecvt_facet* is used for UTF-8 output. // ############################################################################ // # Name: MyLog.h # // # Purpose: Logging Class Header # // # Author: Andrew Drach # // # Modified by: <somebody> # // # Created: 03/21/10 # // # SVN-ID: $Id$ # // # Copyright: (c) 2010 Andrew Drach # // # Licence: <license> # // ############################################################################ #ifndef INCLUDED_MYLOG_H #define INCLUDED_MYLOG_H // headers -------------------------------------------------------------------- #include <string> #include <iostream> #include <fstream> #include <exception> #include <boost/program_options/detail/utf8_codecvt_facet.hpp> using namespace std; // definitions ---------------------------------------------------------------- // ---------------------------------------------------------------------------- // DblBuf class // Splits up output stream into two // Inspired by http://wordaligned.org/articles/cpp-streambufs // ---------------------------------------------------------------------------- class DblBuf : public wstreambuf { private: // private member declarations DblBuf(); wstreambuf *bf1; wstreambuf *bf2; virtual int_type overflow(int_type ch) { int_type eof = traits_type::eof(); int_type not_eof = !eof; if ( traits_type::eq_int_type(ch,eof) ) return not_eof; else { char_type ch1 = traits_type::to_char_type(ch); int_type r1( bf1on ? bf1->sputc(ch1) : not_eof ); int_type r2( bf2on ? bf2->sputc(ch1) : not_eof ); return (traits_type::eq_int_type(r1,eof) || traits_type::eq_int_type(r2,eof) ) ? eof : ch; } } virtual int sync() { int r1( bf1on ? bf1->pubsync() : NULL ); int r2( bf2on ? bf2->pubsync() : NULL ); return (r1 == 0 && r2 == 0) ? 0 : -1; } public: // public member declarations explicit DblBuf(wstreambuf *bf1, wstreambuf *bf2) : bf1(bf1), bf2(bf2) { if (bf1) bf1on = true; else bf1on = false; if (bf2) bf2on = true; else bf2on = false; } bool bf1on; bool bf2on; }; // ---------------------------------------------------------------------------- // logstream class // Wrapper for a standard wostream with access to modified buffer // ---------------------------------------------------------------------------- class logstream : public wostream { private: // private member declarations logstream(); public: // public member declarations DblBuf *buf; explicit logstream(wstreambuf *StrBuf, bool isStd = false) : wostream(StrBuf, isStd), buf((DblBuf*)StrBuf) {} }; // ---------------------------------------------------------------------------- // Logging mode Class // ---------------------------------------------------------------------------- enum LogModes{LogToFile=1, LogToScreen, LogToBoth}; class LogMode { private: // private member declarations LogMode(); short mode; public: // public member declarations LogMode(short mode1) : mode(mode1) {} logstream& operator()(logstream &stream1) { switch(mode) { case LogToFile: stream1.buf->bf1on = true; stream1.buf->bf2on = false; break; case LogToScreen: stream1.buf->bf1on = false; stream1.buf->bf2on = true; break; case LogToBoth: stream1.buf->bf1on = true; stream1.buf->bf2on = true; } return stream1; } }; logstream& operator<<(logstream &out, LogMode mode) { return mode(out); } wostream& TimeStamp1(wostream &out1) { time_t time1; struct tm timeinfo; wchar_t timestr[512]; // Get current time and convert it to a string time(&time1); localtime_s (&timeinfo, &time1); wcsftime(timestr, 512,L"[%Y-%b-%d %H:%M:%S %p] ",&timeinfo); return out1 << timestr; } // ---------------------------------------------------------------------------- // MyLog class // Logs events to both file and screen // ---------------------------------------------------------------------------- class MyLog { private: // private member declarations MyLog(); auto_ptr<DblBuf> buf; string mErrorMsg1; string mErrorMsg2; string mErrorMsg3; string mErrorMsg4; public: // public member declarations explicit MyLog(string FileName1, wostream *ScrLog1, locale utf8locale1); ~MyLog(); void NewEvent(wstring str1, bool TimeStamp = true); string FileName; wostream *ScrLog; wofstream File; auto_ptr<logstream> Log; locale utf8locale; }; // ---------------------------------------------------------------------------- // MyLog constructor // ---------------------------------------------------------------------------- MyLog::MyLog(string FileName1, wostream *ScrLog1, locale utf8locale1) : // ctors mErrorMsg1("Failed to open file for application logging! []"), mErrorMsg2("Failed to write BOM! []"), mErrorMsg3("Failed to write to file! []"), mErrorMsg4("Failed to close file! []"), FileName(FileName1), ScrLog(ScrLog1), utf8locale(utf8locale1), File(FileName1.c_str()) { // Adjust error strings mErrorMsg1.insert(mErrorMsg1.length()-1,FileName1); mErrorMsg2.insert(mErrorMsg2.length()-1,FileName1); mErrorMsg3.insert(mErrorMsg3.length()-1,FileName1); mErrorMsg4.insert(mErrorMsg4.length()-1,FileName1); // check for file open errors if ( !File ) throw ofstream::failure(mErrorMsg1); // write UTF-8 BOM File << wchar_t(0xEF) << wchar_t(0xBB) << wchar_t(0xBF); // switch locale to UTF-8 File.imbue(utf8locale); // check for write errors if ( File.bad() ) throw ofstream::failure(mErrorMsg2); buf.reset( new DblBuf(File.rdbuf(),ScrLog->rdbuf()) ); Log.reset( new logstream(&*buf) ); } // ---------------------------------------------------------------------------- // MyLog destructor // ---------------------------------------------------------------------------- MyLog::~MyLog() { *Log << TimeStamp1 << "Log finished." << endl; // clean up objects Log.reset(); buf.reset(); File.close(); // check for file close errors if ( File.bad() ) throw ofstream::failure(mErrorMsg4); } //--------------------------------------------------------------------------- #endif // INCLUDED_MYLOG_H Tested on MSVC 2008, boost 1.42. I do not know if this is the right place to share it. Hope it helps anybody. Feel free to make it better.

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  • Rails: three most recent comments for unique users

    - by Dennis Collective
    class User has_many :comments end class Comment belongs_to :user named_scope :recent, :order => 'comments.created_at DESC' named_scope :limit, lambda { |limit| {:limit => limit}} named_scope :by_unique_users end what would I put in the :by_unique_users so that I can do Comment.recent.by_unique_users.limit(3), and only get one comment per user

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  • iphones inbuilt mail composer

    - by hardik
    Hello everyone i am new to i phone development i have a requirement that my email us field is coming from webservice on tapping it the iphones email composer gets open if i want to add a button on iphones in built mail composer i could i do that please guide me to do that a sample code would be a boost

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  • Translate C# code into AST?

    - by Erik Forbes
    Is it currently possible to translate C# code into an Abstract Syntax Tree? Edit: some clarification; I don't necessarily expect the compiler to generate the AST for me - a parser would be fine, although I'd like to use something "official." Lambda expressions are unfortunately not going to be sufficient given they don't allow me to use statement bodies, which is what I'm looking for.

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  • twisted reactor stops too early

    - by pygabriel
    I'm doing a batch script to connect to a tcp server and then exiting. My problem is that I can't stop the reactor, for example: cmd = raw_input("Command: ") # custom factory, the protocol just send a line reactor.connectTCP(HOST,PORT, CommandClientFactory(cmd) d = defer.Deferred() d.addCallback(lambda x: reactor.stop()) reactor.callWhenRunning(d.callback,None) reactor.run() In this code the reactor stops before that the tcp connection is done and the cmd is passed. How can I stop the reactor after that all the operation are finished?

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  • Optimizing sorting container of objects with heap-allocated buffers - how to avoid hard-copying buff

    - by Kache4
    I was making sure I knew how to do the op= and copy constructor correctly in order to sort() properly, so I wrote up a test case. After getting it to work, I realized that the op= was hard-copying all the data_. I figure if I wanted to sort a container with this structure (its elements have heap allocated char buffer arrays), it'd be faster to just swap the pointers around. Is there a way to do that? Would I have to write my own sort/swap function? #include <deque> //#include <string> //#include <utility> //#include <cstdlib> #include <cstring> #include <iostream> //#include <algorithm> // I use sort(), so why does this still compile when commented out? #include <boost/filesystem.hpp> #include <boost/foreach.hpp> using namespace std; namespace fs = boost::filesystem; class Page { public: // constructor Page(const char* path, const char* data, int size) : path_(fs::path(path)), size_(size), data_(new char[size]) { // cout << "Creating Page..." << endl; strncpy(data_, data, size); // cout << "done creating Page..." << endl; } // copy constructor Page(const Page& other) : path_(fs::path(other.path())), size_(other.size()), data_(new char[other.size()]) { // cout << "Copying Page..." << endl; strncpy(data_, other.data(), size_); // cout << "done copying Page..." << endl; } // destructor ~Page() { delete[] data_; } // accessors const fs::path& path() const { return path_; } const char* data() const { return data_; } int size() const { return size_; } // operators Page& operator = (const Page& other) { if (this == &other) return *this; char* newImage = new char[other.size()]; strncpy(newImage, other.data(), other.size()); delete[] data_; data_ = newImage; path_ = fs::path(other.path()); size_ = other.size(); return *this; } bool operator < (const Page& other) const { return path_ < other.path(); } private: fs::path path_; int size_; char* data_; }; class Book { public: Book(const char* path) : path_(fs::path(path)) { cout << "Creating Book..." << endl; cout << "pushing back #1" << endl; pages_.push_back(Page("image1.jpg", "firstImageData", 14)); cout << "pushing back #3" << endl; pages_.push_back(Page("image3.jpg", "thirdImageData", 14)); cout << "pushing back #2" << endl; pages_.push_back(Page("image2.jpg", "secondImageData", 15)); cout << "testing operator <" << endl; cout << pages_[0].path().string() << (pages_[0] < pages_[1]? " < " : " > ") << pages_[1].path().string() << endl; cout << pages_[1].path().string() << (pages_[1] < pages_[2]? " < " : " > ") << pages_[2].path().string() << endl; cout << pages_[0].path().string() << (pages_[0] < pages_[2]? " < " : " > ") << pages_[2].path().string() << endl; cout << "sorting" << endl; BOOST_FOREACH (Page p, pages_) cout << p.path().string() << endl; sort(pages_.begin(), pages_.end()); cout << "done sorting\n"; BOOST_FOREACH (Page p, pages_) cout << p.path().string() << endl; cout << "checking datas" << endl; BOOST_FOREACH (Page p, pages_) { char data[p.size() + 1]; strncpy((char*)&data, p.data(), p.size()); data[p.size()] = '\0'; cout << p.path().string() << " " << data << endl; } cout << "done Creating Book" << endl; } private: deque<Page> pages_; fs::path path_; }; int main() { Book* book = new Book("/some/path/"); }

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  • Load Pymacs & Ropemacs only when opening a Python file ?

    - by Mtgred
    I use Pymacs to load Ropemacs and Rope with the following lines in my .emacs as described here. (autoload 'pymacs-load "pymacs" nil t) (pymacs-load "ropemacs" "rope-") It however slowdown the startup of Emacs significantly as it takes a while to load Ropemacs. I tried the following line instead but that loads Ropemacs everytime a Python file opened... (add-hook 'python-mode-hook (lambda () (pymacs-load "ropemacs" "rope-"))) Is there a way to perform the pymacs-load when opening a Python file but only if ropemacs and rope aren't loaded yet?

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