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  • Forcing a templated object to construct from a pointer

    - by SalamiArmi
    I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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  • Is this a correct implementation of singleton C++?

    - by Kamal
    class A{ static boost::shared_ptr<A> getInstance(){ if(pA==NULL){ pA = new A(); } return boost::shared_ptr(pA); } //destructor ~A(){ delete pA; pA=NULL; } private: A(){ //some initialization code } //private assigment and copy constructors A(A const& copy); // Not Implemented A& operator=(A const& copy); // Not Implemented static A* pA; }; A* A::pA = NULL;

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  • What is Ruby's double-colon (::) all about?

    - by Meltemi
    I'd probably be able to answer this for myself if "::" wasn't so hard to Google. Didn't see anything on SO so thought I'd try my luck. What is this double-colon :: all about? I see it everywhere in Rails: class User < ActiveRecord::Base or… ActionController::Routing::Routes.draw do |map| I found a definition from this guy: The :: is a unary operator that allows: constants, instance methods and class methods defined within a class or module, to be accessed from anywhere outside the class or module. but that just leads to more questions. What good is scope (private, protected) if you can just use :: to expose anything?

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  • Find top N elements in a Multiset from Google Collections?

    - by dfrankow
    A Google Collections Multiset is a set of elements each of which has a count (i.e. may be present multiple times). I can't tell you how many times I want to do the following Make a histogram (exactly Multiset) Get the top N values from the histogram Examples: top 10 URLs, top 10 tags, ... What is the canonical way to do #2 given a Multiset? Here is a blog post about it, but that code is not quite what I want. First, it returns everything, not just top N. Second, it copies (is it possible to avoid a copy?). Third, I usually want a deterministic sort, i.e. tiebreak if counts are equal.

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  • Extension method question. Why do I need to use someObj = someObj.somemethod();

    - by Kettenbach
    Hi All, I have a simple extension method that I would like to use to add an item to an array of items. public static T[] addElement<T>(this T[] array, T elementToAdd) { var list = new List<T>(array) {elementToAdd}; return list.ToArray(); } this works ok, but when I use it, I am having to set the array equal to the return value. I see that I am returning an Array. I likely want this method to be void, but I would like the item added. Does anyone have any ideas on what I need to do , to make this work the way I am wanting? Instead of someArray = someArray.addElement(item), I just want to do someArray.addElement(item) and then someArray be ready to go. What am I missing here? Thanks, ~ck in San Diego

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  • What happens when a computer program runs?

    - by gaijinco
    I know the general theory but I can't fit in the details. I know that a program resides in the secondary memory of a computer. Once the program begins execution it is entirely copied to the RAM. Then the processor retrive a few instructions (it depends on the size of the bus) at a time, puts them in registers and executes them. I also know that a computer program uses two kinds of memory: stack and heap, which are also part of the primary memory of the computer. The stack is used for non-dynamic memory, and the heap for dynamic memory (for example, everything related to the new operator in C++) What I can't understand is how those two things connect. At what point is the stack used for the execution of the instructions? Instructions go from the RAM, to the stack, to the registers?

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  • 128bit hash comparison with SSE

    - by fokenrute
    Hi, In my current project, I have to compare 128bit values (actually md5 hashes) and I thought it would be possible to accelerate the comparison by using SSE instructions. My problem is that I can't manage to find good documentation on SSE instructions; I'm searching for a 128bit integer comparison instruction that let me know if one hash is larger, smaller or equal to another. Does such an instruction exists? PS: The targeted machines are x86_64 servers with SSE2 instructions; I'm also interested in a NEON instruction for the same job.

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  • checking boolean property in XML(Spring)

    - by Abhishek Bhandari
    I am using Spring Framework . While writing coustum SQL queries , i am unable check a parameter of boolean value. For example this is not working .. do some SQl cods The above checking is not working , it is evaluating as equal in both the cases when booleanVariable is true and false . i tried to replace compareValue ="tree" and "false". As that is a monkey work i do sometimes . is it possible to check the boolean property in XML like above .

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  • How to validate the following

    - by user281180
    I have the following code <% using(Ajax.BeginForm("UpdatePassword", new AjaxOptions{UpdateTargetId="Password"})) { %> <div id="Password"> <table> <tr> <td>New password</td><td><%=Html.Password("newPassword") %></td> </tr> <tr> <td>Confirm new password</td> <td><%=Html.Password("confirmPassword")%><%= Html.ValidationMessage("confirmPassword") %> </td> </tr> </table> <% } % Can someone help me how to proceed to validating that the confirmPassword is equal the new password, and if not the message is displayed in the html.validationMessage()...

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  • How can I find out how many rows of a matrix satisfy a rather complicated criterion (in R)?

    - by Brani
    As an example, here is a way to get a matrix of all possible outcomes of rolling 4 (fair) dice. z <- as.matrix(expand.grid(c(1:6),c(1:6),c(1:6),c(1:6))) As you may already have understood, I'm trying to work out a question that was closed, though, in my opinion, it's a challenging one. I used counting techniques to solve it (I mean by hand) and I finaly arrived to a number of outcomes, with a sum of subset being 5, equal to 1083 out of 1296. That result is consistent with the answers provided to that question, before it was closed. I was wondering how could that subset of outcomes (say z1, where dim(z1) = [1083,4] ) be generated using R. Do you have any ideas? Thank you.

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  • Parsing a comma-separated list

    - by alex
    I have a comma-separated list of values, for example: strins s = "param1=true;param2=4;param3=2.0f;param4=sometext;"; I need a functions: public bool ExtractBool(string parameterName, string @params); public int ExtractInt(string parameterName, string @params); public float ExtractFloat(string parameterName, string @params); public string ExtractString(string parameterName, string @params); Is there a special functions in .net that can help me with csl ? PS: parameter names are equal within a list.

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  • Calling this[int index] via reflection

    - by tkutter
    I try to implement a reflection-based late-bound library to Microsoft Office. The properties and methods of the Offce COM objects are called the following way: Type type = Type.GetTypeFromProgID("Word.Application"); object comObject = Activator.CreateInstance(type); type.InvokeMember(<METHOD NAME>, <BINDING FLAGS>, null, comObject, new object[] { <PARAMS>}); InvokeMember is the only possible way because Type.GetMethod / GetProperty works improperly with the COM objects. Methods and properties can be called using InvokeMember but now I have to solve the following problem: Method in the office-interop wrapper: Excel.Workbooks wb = excel.Workbooks; Excel.Workbook firstWb = wb[0]; respectively foreach(Excel.Workbook w in excel.Workbooks) // doSmth. How can I call the this[int index] operator of Excel.Workbooks via reflection?

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  • Get the affinity of a SQLite column on Android

    - by Neil Traft
    The SQLite C library has a method, sqlite3_column_decltype(). But I cannot find any place where the Android SQLite API makes this method available. Is there any way to get the declared type of a column without running any SQL (i.e. can I avoid using PRAGMA table_info)? I could have used AbstractWindowedCursor.isBlob(), but it says that it will also return true if the field is NULL. I need something that will guarantee me a value equal to the column's declared type.

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  • C++ refactor common code with one different statement

    - by user231536
    I have two methods f(vector<int>& x, ....) and g(DBConn& x, ....) where the (....) parameters are all identical. The code inside the two methods are completely identical except for one statement where we do different actions based on the type of x: in f(): we do x.push_back(i) in g(): we do x.DeleteRow(i) What is the simplest way to extract the common code into one method and yet have the two different statements? I am thinking of having a templated functor that overloads operator () (int a) but that seems overkill.

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  • On Memory Allocation and C++

    - by Arpan
    And I quote from MSDN http://msdn.microsoft.com/en-us/library/aa366533(VS.85).aspx: The malloc function has the disadvantage of being run-time dependent. The new operator has the disadvantage of being compiler dependent and language dependent. Now the questions folks: a) What do we mean that malloc is run-time dependent? What kind of dynamic memory allocation functions can be independent of run-time? This statement sounds real strange. b) new is language dependent? Of course it should be right? Are HeapAlloc, LocalAlloc etc language independent? c) From a pure performance perspective are the MSVC provided routines preferable? Arpan

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  • Unreachable code detected in case statement

    - by alex
    I have a code: protected override bool ProcessCmdKey(ref Message msg, Keys keyData) { switch (keyData) { case Keys.Alt|Keys.D1: if (this._condition1) { return true; } else { return base.ProcessCmdKey(ref msg, keyData); } break; case Keys.Control |Keys.U: if (this._condition2) { return true; } else { return base.ProcessCmdKey(ref msg, keyData); } break; default: return base.ProcessCmdKey(ref msg, keyData); } return true; It gives me "unreachable code detected" warning on breaks. Is it good practice not to use break operator here ? I don't want to turn off "unreachable code detected" warning. PS: There are many case in my ProcessCmdKey method.

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  • How to Detect Trusted Connection in Crystal Reports using VB.NET?

    - by Michael
    I have some Crystal Reports connecting to a Sql Server db that I would like to detect whether the connection is trusted or whether I need to supply the log on info (reports are not supplied by me so I can't control the connect method). If I just blindly supply login credentials, it won't connect if it is a trusted connection. The following does not work: oRpt = oCR.OpenReport("C:\MyReport.rpt") if oRpt.Database.Tables(1).ConnectionProperties.Item("Integrated Security") = True then 'trusted connection else 'supply login credentials end if It gives the following error: Operator '=' is not defined for type 'IConnectionProperty' and type 'Boolean'. I cannot find how create a construct in vb.net for IConnectionProperty. I can't find any documents from Crystal that explain it. I am using Crystal Reports XI - Developer

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  • How to call a bool function...

    - by Gerri
    Hello, I did not see anything that address my particular code problem. I have a bool function in a class; the bool function is named: bool Triplet::operator ==(const Triplet& operand)const And I am trying to call it in Main but having problems just getting the call right. Apparently if I leave out any thing in the wording it gives an error that I have too few aruguments and if I try to use the entire wording of the function, I get the error that I need a semi-colon, but I already have a semi-colon at the end of the call, so I know that something else is wrong and I simply cannot figure out what is wrong! Any help would be appreciated! Thanks in advance.

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  • jQuery basics - selector

    - by rkrauter
    I feel dumb.. Why is my "header" div not being selected? It's background color is not being changed. I am learning about the + operator so I am not looking for a different selector. E + F an F element immediately preceded by an E element $("#divA + div").css("background-color", "red"); Html <div id="divA"> <div> Header</div> Lorem Ipsum is simply dummy text of the printing and typesetting industry. </div> Thanks!

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  • Purpose of boost::checked_delete

    - by Channel72
    I don't understand the purpose of boost::checked_delete. The documentation says: The C++ Standard allows, in 5.3.5/5, pointers to incomplete class types to be deleted with a delete-expression. When the class has a non-trivial destructor, or a class-specific operator delete, the behavior is undefined. Some compilers issue a warning when an incomplete type is deleted, but unfortunately, not all do, and programmers sometimes ignore or disable warnings. The supplied function and class templates can be used to prevent these problems, as they require a complete type, and cause a compilation error otherwise. So the C++ standard allows you to delete incomplete types, which causes undefined behavior if the type has a non-trivial destructor. What? How can an incomplete type have any destructor at all? Isn't an incomplete type just a prototype?

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  • Creating a pie chart for an app

    - by jhodgson4
    I'm developing an app which requires a pie chart to display a set number of modules. The modules need to be clickable, sending a value to the database for how many times the module has been clicked. The slices will change color etc depending on this database value. The slices will always be equal in size. All simple stuff. My question is what charting system would you use. I've been looking at google charts but I have no way of registering a value in a slice without changing its 'weight' in the chart. So ideally I would like to add data-stage="2" to each slice that I can access with a custom method. Also google charts seems quite heavy for what I need? Any advice would be greatly appreciated. Joe

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  • How to concatenate multiple lines of log file into single variable in batch file?

    - by psych
    I have a log file containing a stack trace split over a number of lines. I need to read this file into a batch file and remove all of the lines breaks. As a first step, I tried this: if exist "%log_dir%\Log.log" ( for /F "tokens=*" %%a in ("%log_dir%\Log.log") do @echo %%a ) My expectation was that this would echo out each line of the log file. I was then planning to concatenate these lines together and set that value in a variable. However, this code doesn't do what I would expect. I have tried changing the value of the options for delims and tokens, but the only output I can get is the absolute path to the log file and nothing from the contents of this file. How can I set a variable to be equal to the lines of text in a file with the line breaks removed?

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  • Php getting too many connections error from MySQL

    - by uzioriluzan
    Hello everyone, I am using MySQL and PHP with 2 application servers and 1 database server. With the increase of the number of users (around 1000 by now), I'm getting the following error : SQLSTATE[08004] [1040] Too many connections The parameter "max_connections" is set to "1000" in my.cnf and "mysql.max_persistent" is set to -1 in php.ini. There are at most 1500 apache processes running at a time since the "MaxClients" apache parameter is equal to 750 and we have 2 application servers. Should I raise the "max_connections" to 1500 as indicated in here? Or should I set "mysql.max_persistent" to 750 (we use PDO with persistent connections for performance reasons since the database server is not the same as the application servers)? Or should I try something else? Thanks in advance!

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  • How it is better to organise a large database of addresses?

    - by shurik2533
    How it is better to organise a large database of addresses? It is need to create mysql database of addresses. How it is better for organising? I have two variants: 1) cuontries id|name 1 |Russia cities id|name 1 |Moscow 2 |Saratov villages id|name streets id|name 1 |Lenin st. places id|name |country_id|city_id|village_id|street_id|building_number|office|flat_number|room_number 1 |somebuilding |1 |1 |NULL |1 |31 |12a |NULL |NULL For simplification I use not all making addresses. If any part does not participate in the address it is equal NULL 2) addressElements id|name 1 |country 2 |city 3 |village 4 |street 5 |office 6 |flat_number 7 |room_number addressValues id|addressElement_id|value 1 |1 |Russia 2 |2 |Saratov 3 |2 |Moscow 4 |3 |Prostokvashino 5 |4 |Lenin st. places id| name 1 | somebuilding places_has_addressValues place_id|addressValue_id 1 |1 1 |3 1 |5 UPD. I have decided to make as follows

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  • bitfield mask calculation macro

    - by Aidan Cully
    We have a set of C macros, here, for using the preprocessor to do bitfield operations, and we run into warnings when attempting to use these macros in visual studio. The problem can be demonstrated very easily: #define BITFIELD_WIDTHMASK(Width) \ ((Width) >= 32 ? ~0x0ul : (1ul << (Width)) - 1) unsigned long foo(void) { return BITFIELD_WIDTHMASK(32); } Compiling this with MSVC yields the warning: test.c(12) : warning C4293: '<<' : shift count negative or too big, undefined behavior This isn't a behavior problem - the << operator won't be used in this case, and that should be detected at compile time. But does anyone have any suggestions about how to rewrite the macro to avoid the warning? Or, failing that, how to redesign the macro interface for this? Thanks in advance

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