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C++17 新功能 try_emplace 回顧 emplace 大家的好朋友 Standard Template Library (STL) 容器提供如 push_back , insert 等介面，讓我們塞東西進去； C++11 之後，新增了 emplace 系列的介面，如 std::vector::emplace_back , std::map::emplace 等，差異在於 emplace 是在容器內 in-place 直接建構新元素，而不像 push_back 在傳遞參數前建構，下面用實例來說明： struct Value { // ctor1 Value ( int size ) : array ( new char [ size ] ) , size ( size ) { printf ( "ctor1: %d\n" , size ) ; } // ctor2 Value ( const Value & v ) : array ( new char [ v . size ] ) , size ( v . size ) { printf ( "ctor2: %d\n" , size ) ; memcpy ( array . get ( ) , v . array . get ( ) , size ) ; } private : std :: unique_ptr < char [ ] > array ; int size = 0 ; } ; struct Value 定義了自訂建構子 (ctor1)，以指定大小 size 配置陣列，複製建構子 (ctor2) 則會配置與來源相同大小及內容的陣列，為了方便觀察加了一些 printf 。當我們如下使用 std::vector::push_back 時 std :: vector < Value > v ; v . push_back ( Value ( 2048 ) ) ; 首先 Value 會先呼叫 ctor1，傳給 push_ba...

KNN Text Classification Simplified Data Set Assume terms a document are unique (tag-like dataset). doc terms d0 [ t0, t2, t3 ] d1 [ t1, t3 ] d2 [ t0, t2 ] and docs = [ d0, d1, d2 ] d0.terms = [ t0, t2, t3 ] Weight of Terms Represent weight of terms with a term-by-document Matrix, A, where ti denotes term i and dj denotes document j . Entry A(i, j) is computed by TF-IDF . For example: A(0, 0) = (1 / # of terms of d0) * log2(# of docs / t0 occurrences for all docs) = (1/3) * log2(3/2) ~= 0.195 Hence A of the dataset is term\doc d0 d1 d2 t0 0.195 0 0.292 t1 0 0.792 0 t2 0.195 0 0.292 t3 0.195 0.292 0 Note : t0 … t3 can be viewed as a multi-dimension space such that d0 is a point (0.195, 0, 0.195, 0.195) of the space. Document Similarity Per the weight matrix we can compute document-to-document similarities matrix, S, by cosine-similarity. For example: intersect(d0.terms, d0.terms) = ...

PST: Fast Float Serialization Given float numbers of precision 3 (rounded to decimal places), e.g. 0.123. Following method can de/serialize float numbers safely across platforms of different endianness. // Serialization float number [ 100 ] ; std :: ofstream fout ( “output” ) ; for ( int i = 0 ; i < 100 ; ++ i ) fout << ( number * 1000 ) << endl ; // De-serialization int value ; float result [ 100 ] ; std :: ifstream fin ( “input” ) ; for ( int i = 0 ; i < 100 ; ++ i ) { fin >> value ; result [ i ] = value / 1000.0 ; } By translating float number to a discrete form, the cost of de/serialization (text to double) is reduced since it becomes a text to integer conversion. Original posted in my Tumblr Update: Another technique union { int ival ; float fval ; } number ; number . fval = 0.1234 ; fout << number . ival ; fout >> number . ival ; // use number.fval –...

Getting Started with Google Test and CMake on Windows Versions Windows 7 MSVC 11 (Visual Studio 2012) CMake 3.0 gtest 1.7.0 Google Test Assume we placed unzipped gtest source in %GTEST_ROOT% . To get gtest-1.7.0 compiled with MSVC11, edit %GTEST_ROOT%\cmake\internal_utils.cmake . macro ( fix_default_compiler_settings_ ) $ if ( MSVC ) $ add_definitions ( - D_VARIADIC_MAX = 10 ) # Add this line # . . . endif ( ) endmacro ( ) Note : You won’t need the workaround with MSVC12, or VS2013 (I envy you). Open up “Developer Command Prompt for VS2012” (yeah, I LOVE cmdline) and type: # Compile cd %GTEST_ROOT% mkdir build cd build cmake .. -G "NMake Makefiles" # Install with prefix "c:\opt" ( change it to whatever you like ) mkdir c:\opt\lib mkdir c:\opt\include xcopy *.lib c:\opt\lib cd .. xcopy include\gtest c:\opt\include\ Note : I actually did files/dirs copying in cygwin and welcome feedback for...

Pyinstaller on Windows Prerequisites 64-bit Windows 2008/7 Python 2.7.10 x86 1 pip virtualenv Microsoft Visual C++ 2008 Redistributable Package (x86) or MSVC Compiler for Pyhton 2.7 2 Create and activate virtualenv virtualenv c:\venv\pyapp cd c:\venv\pyapp\Scripts activate From now on, we’ll be working within a virtualenv environment. PowerShell If you would like to give PowerShell a try like me. Before activate your virtualenv , you need to change your script execution policy via Set-ExecutionPolicy RemoteSigned in a privileged PowerShell terminal. Install pywin32 and pyinstaller easy_install http://sourceforge.net/projects/pywin32/files/pywin32/Build %20219 /pywin32 -219 .win32-py2. 7 .exe /download pip install pyinstaller The msvcr90.dll Problem There is a known issue was discussed on StackOverflow . Quick solution is to install the specific Microsoft Visual C++ 2008 Redistributable Package (x86) which can be downloaded here . If...

ExtJS MVC Architecture Model is persistent in server side. Store is cache of model thru its proxy. Controller connect View and data in Store. Controller responds users’ operations over View. View presents binded data and input widgets to users. Application Files Root Second Third Forth / Fifth Fifth MyApp / + ext-4 /<extjs_code> + index.html + app.js + app / + + controller /Main.js + + model /Main.js + + store /Main.js + + view / + + + Viewport.js + + + main / + + + + Act1.js + + + + Act2.js + data / + + main.json + + updatemain.json index.html < html > < head > < title > Account Manager </ title > <!-- Load ExtJS style sheet and scripts --> < link rel = " stylesheet " type = " text/css " href = " ext-4/resources/css/ext-all.css " > ...

Exception Translation from C++ to Python with Boost.Python Scenario Say we have written a Python binding with Boost.Python. Something like following code. // some.cpp # include <stdexcept> # include <boost/python.hpp> struct my_exception : std :: exception { my_exception ( int extra_info ) : extra_info ( extra_info ) { } char const * what ( ) noexcept ( true ) { return "My exception" ; } int const extra_info ; } ; void do_throw ( ) { throw my_exception ( ) ; } // Something should be done here ... BOOST_PYTHON_MODULE ( MyLib ) { using namespace boost :: python ; def ( "do_throw" , & do_throw ) ; } And we wish to catch a Python exception object in Python code, e.g. import MyLib try : MyLib . do_throw ( ) except MyLib . MyException as e : print e , e . extra_info pass The situation is, we can’t directly pass the exception object, my_exception,...

Boyer Moore String Matching in D Lang 下雨的假日就是要寫程式啊！ 演算法本身請看 參考資訊 先來個介面 import std . stdio ; import std . algorithm : max ; void boyer_moore_matching ( T ) ( T [ ] text , T [ ] pattern ) { // TODO: 印出每個 matching 的 index } void main ( ) { boyer_moore_matching ! char ( "AABCABABCABABA" . dup , "ABABA" . dup ) ; } import module 會引入所有 module expose 的類別、函數，也可以只引入部分功能，例如 import std.algorithm: max; 只會引入 max 字串常數 (string) 是 immutable 所以要用 dup (duplicate) 動態複製，複製體型別為 char[] ( 背景故事連結 ) 一上來就用泛形介面 i.e. auto func(T)(T arg) 這邊 T 可以是任何型別 呼叫泛型函數要用 ! 後面接型別，多個型別可以用 func!(type1, type2)(arg) 的方式 這個介面有個問題，因為字串比對不需要修改 text 或是 pattern ，應該要讓這兩個參數型別是個常量，這樣也能省去兩次複製 (dup)。 import std . stdio ; void boyer_moore_matching ( T ) ( const T [ ] text , const T [ ] pattern ) { // TODO: 印出每個 matching 的 index } void main ( ) { boyer_moore_matching ! char ( "AABCABABCABABA" , "ABABA" ) ; } 前處理之一 (...