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  • What is the best solution to replace a new memory allocator in an existing code?

    - by O. Askari
    During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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  • C++ / Java: Toggle boolean statement?

    - by Martijn Courteaux
    Hi, Is there a short way to toggle a boolean? With integers we can do operations like this: int i = 4; i *= 4; // equals 16 /* Which is equivalent to */ i = i * 4; So is there also something for booleans (like the *= operator for ints)? In C++: bool booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something? In Java: boolean booleanWithAVeryLongName = true; booleanWithAVeryLongName = !booleanWithAVeryLongName; // Can it shorter? booleanWithAVeryLongName !=; // Or something?

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  • Why does a Linq Cast<T> operation fail when I have an implicit cast defined?

    - by Ryan Versaw
    I've created two classes, with one of them having an implicit cast between them: public class Class1 { public int Test1; } public class Class2 { public int Test2; public static implicit operator Class1(Class2 item) { return new Class1{Test1 = item.Test2}; } } When I create a new list of one type and try to Cast<T> to the other, it fails with an InvalidCastException: List<Class2> items = new List<Class2>{new Class2{Test2 = 9}}; foreach (Class1 item in items.Cast<Class1>()) { Console.WriteLine(item.Test1); } This, however, works fine: foreach (Class1 item in items) { Console.WriteLine(item.Test1); } Why is the implicit cast not called when using Cast<T>?

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  • What is wrong with my SQL syntax for an UPDATE with a JOIN?

    - by Phil H
    I have two tables, related by a common key. So TableA has key AID and value Name and TableB has keys AID, BID and values Name, Value: AID Name 74 Alpha AID BID Name Value 74 4 Beta Brilliance I would like to update the TableB Value here from Brilliance to Barmy, using just the Name fields. I thought I could do it via an UPDATE containing a JOIN, but Access (I know...) is complaining with 'Syntax error (missing operator) in query expression ' and then everything from 'Barmy' here: UPDATE tB SET tB.BValue='Barmy' FROM TableB tB INNER JOIN TableA tA ON tB.AID=tA.AID WHERE tB.Name='Beta' AND tA.Name='Alpha'; What is my heinous crime? Or is it just Access not conforming?

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  • Design guidelines for cache mechanism

    - by Delashmate
    Hi All, I got assignment to write design for cache mechanism (this is work assignment, not homework), This is my first time writing a design document, Our program display images for doctors, and we want to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas: Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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  • CodeIgniter URI segments captured as variables?

    - by Zen Savona
    well, i have a function within a controller called test, and i can access it by going to http://localhost/nwk/control/test this is my function. I want to use the data given in the next segment from the "test" as a php variable. so if i put function test() { $var $this->uri->segment(3); echo $var; } according to the user guide if I enter control/test/data, my variable should be equal to 'data'? doesn't seem to be working. Am I missing something here?

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  • C# logic order and compiler behavior

    - by Terrapin
    In C#, (and feel free to answer for other languages), what order does the runtime evaluate a logic statement? Example: DataTable myDt = new DataTable(); if (myDt != null && myDt.Rows.Count > 0) { //do some stuff with myDt } Which statement does the runtime evaluate first - myDt != null or: myDt.Rows.Count > 0 ? Is there a time when the compiler would ever evaluate the statement backwards? Perhaps when an "OR" operator is involved?

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  • C# Comparison shorthand

    - by TheAdamGaskins
    I have this code: if (y == a && y == b && y == c && y == d ...) { ... } Is there some form of shorthand so that I can rewrite it as something like this? if(y == (a && b && c && d ...)) { ... } The functionality should be exactly the same. I'm just looking for something that looks less confusing. EDIT Sorry for not clarifying, all the variables are integers. I'm looking for a shorter way to ensure that a, b, c, d, ... all equal y.

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  • Using pipes inside a class in C++

    - by Paul
    I'm trying to use this tutorial to make plots with Gnuplot in C++. However I will be using the pipe to Gnuplot from within a class, but then I run into some problems: I've got a header file where I declare all variables etc. I need to declare the pipe-variable here too, but how do I do that? I've tried doing it straight away, but it doesn't work: Logger.h: class Logger { FILE pipe; } Logger.cpp: Logger::Logger() { //Constructor *pipe = popen("gnuplot -persist","w"); } Gives the error Logger.cpp:28: error: no match for ‘operator=’ in ‘*((Logger*)this)->Logger::pipe = popen(((const char*)"gnuplot -persist"), ((const char*)"w"))’ Suggestions?

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  • How to use PHP to POST to a web page then get the results back, locally

    - by Patrick Gates
    I have a page on my web server that is PHP that is set to do this if ($_POST['post'] == true) { echo: 'hello, world'; } I want to create a page that calls to that page, posts "post" equal to "true" and then returns the value "hello, world". I have a script that works, but only if the pages are on different servers. Unfortunately, both of these pages are on the same server, so, heres my code, and I'm hoping you guys can help me, Thank you :) function post($site, $post) { $ch = curl_init(); curl_setopt($ch, CURLOPT_URL,$site); curl_setopt($ch, CURLOPT_FAILONERROR,1); curl_setopt ($ch, CURLOPT_POST, 1); curl_setopt ($ch, CURLOPT_POSTFIELDS, $post); curl_setopt($ch, CURLOPT_FOLLOWLOCATION,1); curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); curl_setopt($ch, CURLOPT_TIMEOUT, 15); $retValue = curl_exec($ch); curl_close($ch); return $retValue; } echo post('data.php', 'post=true');

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  • C++: Vector3 type "wall" ?

    - by anon
    Say I have: class Vector3 { float x, y, z; ... bunch of cuntions .. static operator+(const Vector3&, const Vector3); }; Now, suppose I want to have classes: Position, Velocity, that are exactly like Vector3 (basically, I want typedef Vector3 Position; typedef Vector3 Velocity; Except, given: Position position; Vector3 vector3; Velocity velocity; I want to make sure the following can't happen: position + vector3; vector3 + velocity; velocity + position; What is the best way to achieve this?

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  • Get data from database with two conditions in one list

    - by Kreeki
    Hi coders out there, I'm new to this. I have a (sqlite3, but with ActiveRecord it doesn't matter) table called Messages and a model called Message. I want to find all messages in database that have user_id or reciever_id equal to the object user and his attribute id (for short user.id). I know it's probably just one simple line of code, but I wanna do it the right "rails" way and I don't have much experience with this. I'm using Rails 3. Thanks for any help. Cheers

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  • SQL query: Number of comments posted in last 24 hours by people a user is following

    - by bflora
    I've got a site where users follow users they like and can read their latest updates. I'd like to show my users a simple count of how many comments the people they follow have posted in the last 24 hours. I'm having trouble figuring out the query. I have two tables. comment -cid (comment id) -timestamp -uid (id of person who posted the comment) -comment (content of the comment) user_relationships -requester_id (id of the user who followed the person) -requestee_id (id of the person who was followed) In plain english, I think the query is something like this: COUNT the cid.comment from the comments table where uid.comment is equal to requestee_id.user_relationships associated with requester_id.user_relationships value of X. I need to get all the UIDs of people being followed by a given UID from the user_relationship table. Then count up how many comments those people have posted in the last 24 hours and spit that number out. What would this query look like?

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  • JavaScript eval() with `this`

    - by mojuba
    If I define a JavaScript code snippet in my HTML, like so: <div id=myElem onMyUpdate="alert('Update called for ' + this.id)">... then what is the most elegant way of evaluating it from within JavaScript with this properly assigned? What I came up with so far is something like this: if (elem.hasAttribute('onMyUpdate')) (function () { eval(elem.getAttribute('onMyUpdate')) }).call(elem); which looks terrible (to me), but works. Any better/more elegant alternatives? MDN says there used to be the second argument to eval() for doing just that but it's deprecated now; MDN then suggests to use operator with() instead, which, if you follow the link provided, turns out to be made deprecated by the latest standard. Dead end, in other words. (As a side note, StackOverflow ignores the word this in search terms and thus it may miss relevant answers - is there a way of telling it not to?) Edit: I forgot to mention: no jQuery please, just vanilla JavaScript

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  • prefix and postfix increments while comparing variables

    - by miatech
    could someone explain why this code output is not equals not equals 2 in the first if statement it seems that a = 0 b/c is a postfix increment; therefore a will not increase untile next line; however, the two a's are not equal why? and in the second if when I run the debugger the value of a is 2, but the test is false, why? public static void main (String[] args) { int a = 0; if (a++ == a++) { System.out.println("equals"); } else { System.out.println("not equals"); } if (++a == 2) { System.out.println("equals 2"); } else { System.out.println("not equals 2"); } }

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  • I serialized a C++ object, how to allocate memory for it without knowing what type it is?

    - by Neo_b
    Hello, I have serialized a C++ object and I wish to allocate space for it, although I can't use the "new" operator, because I do not know the object's class. I tried using malloc(sizeof(object)), although trying to typecast the pointer to the type the serialized object is of, the program shut down. Where is the information about the object class stored? class object { public: virtual void somefunc(); int someint; }; class objectchild:public object { } object *o=(object*)malloc(sizeof(objectchild)); cout << int(dynamic_cast<objectchild*>(o)) << endl; This causes a program shutdown. Thank you in advance.

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  • Assigning two strings together getting Access Read Violation

    - by Jay Bell
    I am trying to pass a string to a class mutator and set the private member to that string here is the code that is sending the string void parseTradePairs(Exchange::Currency *curr, std::string *response, int begin, int exit) { int start; int end; string temp; string dataResponse; CURL *tempCurl; initializeCurl(tempCurl); int location = response->find("marketid", begin); if(location <= exit) { start = location + 11; begin = response->find("label", start); end = begin - start - 3; findStrings(start, end, temp, response); getMarketInfo(tempCurl, temp, dataResponse); curr->_coin->setExch(temp); // here is the line of code that is sending the string dataResponse >> *(curr->_coin); curr->_next = new Exchange::Currency(curr, curr->_position + 1); parseTradePairs(curr->_next, response, begin, exit); } } and here is the mutator within the coin class that is receiving the string and assigning it to _exch void Coin::setExch(string exch) { _exch = exch; } I have stepped through it and made sure that exch has the string in it. "105" but soon as it hits _exch = exch; I get the reading violation. I tried passing as pointer as well. I do not believe it should go out of scope. and the string variable in the class is initialized to zero in the default constructor but again that should matter unless I am trying to read from it instead of writing to it. /* defualt constructor */ Coin::Coin() { _id = ""; _label = ""; _code= ""; _name = ""; _marketCoin = ""; _volume = 0; _last = 0; _exch = ""; } Exchange::Exchange(std::string str) { _exch = str; _currencies = new Currency; std::string pair; std::string response; CURL *curl; initializeCurl(curl); getTradePairs(curl, response); int exit = response.find_last_of("marketid"); parseTradePairs(_currencies, &response, 0, exit); } int main(void) { CURL *curl; string str; string id; Coin coin1; initializeCurl(curl); Exchange ex("cryptsy"); curl_easy_cleanup(curl); system("pause"); return 0; } class Exchange { public: typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() : _next(NULL), _prev(NULL), _position(0) {} Coin *_coin; Currency *_next; Currency *_prev; int _position; }; /* constructor and destructor */ Exchange(); Exchange(std::string str); ~Exchange(); /* Assignment operator */ Exchange& operator =(const Exchange& copyExchange); /* Parse Cryptsy Pairs */ friend void parseTradePairs(Currency *curr, std::string *response, int begin, int exit); private: std::string _exch; Currency *_currencies; }; here is what i changed it to to fix it. typedef struct Currency { Currency(Coin *coin, Currency *next, Currency *prev, int position) : _coin(coin), _next(next), _prev(prev), _position(position) {} Currency(Currency *prev, int position) : _prev(prev), _position(position), _next(NULL), _coin(&Coin()){} Currency() { _next = NULL; _prev = NULL; _position = 0; _coin = new Coin(); } Coin *_coin; Currency *_next; Currency *_prev; int _position; };

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  • Query for multiple joins

    - by Shailaja
    i have 3 tables named dataset,dataelem and transformdataelem with column names as below: main.Dataset ------------ datasetID (PK) applicationID main.Dataelem ------------- dataelemID(PK) datasetID(FK) dataelemname biztermID main.Transformdataelem ---------------------- OutputdataelemID InputdataelemID My requirement is: All tables are referenced. Extract all the dataelemId rows from dataelem table where applicationID of dataset table is equal to 1044 and biztermid shud be null. Then whatever resultant dataelemIDs from the above query should be matched with outputdataelemID of Transformdataelem table and we shud get the respective input dataelemId's. Again with these matched inputdataelemID's we shud get the dataelemname's from datelem table.

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  • Compare a DateTime to the current date

    - by looloobs
    Hi I am trying to use a condition on events when the start_at DateTime is equal to or greater than Today's date. I want to list upcoming events, but clearly they are not upcoming if they have already passed. I have: @appointments = Event.find(:all, :conditions => ['move_id = ? AND start_at = ?', @move.id, Date.today]) I think I may be comparing apples and oranges here. It doesn't throw and error, just doesn't do what it is supposed to. Help! Thanks in advance.

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  • Use CSS (and maybe JavaScript) to make an element be square (or maintain a specific aspect ratio)

    - by David Pfeffer
    I have a div that I want to have the following characteristics: Width = 50% of its parent element Height equal to whatever it needs to be in order to maintain a certain aspect ratio. I need to use percentages because the object will resize left-right when the browser is resized. I want the object to be resized top-bottom to ensure the object maintains the same aspect ratio. I don't think there's any way to use pure CSS to do this, but does anyone know of a way? Alternatively, is there an easy JavaScript way to do this? (JQuery is fine.)

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  • How do I iterate over a tuple

    - by Caligo
    How can I iterate over a tuple starting from, say, index 1 to 2? The following doesn't work. using boost::fusion::cons; typedef cons<A, cons<B, cons<C, cons<D> > > > MyTuple; MyTuple tuple_; template <class T> struct DoSomething{ DoSomething(T& t) : t_(&t){ } template <class U> void operator()(U u){ boost::fusion::at<mpl::int_<u> >(*t_); } T* t_; }; boost::mpl::for_each< boost::mpl::range_c<int, 1, 3> >( DoSomething<MyTuple>(tuple_) );

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  • Access SQL query to SELECT from one table and INSERT into another

    - by typoknig
    Below is my query. Access does not like it, giving me the error Syntax error (missing operator) in query expression 'answer WHERE question = 1'. Hopefully you can see what I am trying to do. Please pay particular attention to 3rd, 4th, and 5th lines under the SELECT statement. INSERT INTO Table2 (respondent,1,2,3-1,3-2,3-3,4,5) SELECT respondent, answer WHERE question = 1, answer WHERE question = 2, answer WHERE answer = 'text 1' AND question = 3, answer WHERE answer = 'text 2' AND question = 3, answer WHERE answer = 'text 3' AND question = 3, answer WHERE question = 4, longanswer WHERE question 5 FROM Table1 GROUP BY respondent;

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  • Is it possible to have a variadic function in C with no non-variadic parameter?

    - by Tim
    I have the following function: void doStuff(int unusedParameter, ...) { va_list params; va_start(params, unusedParameter); /* ... */ va_end(params); } As part of a refactor, I'd like to remove the unused parameter without otherwise changing the implementation of the function. As far as I can tell, it's impossible to use va_start when you don't have a last non-variadic parameter to refer to. Is there any way around this? Background: It is in fact a C++ program, so I could use some operator-overloading magic as suggested here, but I was hoping not to have to change the interface at this point. The existing function does its work by requiring that the variable argument list be null-terminated, and scanning for the NULL, therefore it doesn't need a leading argument to tell it how many arguments it has.

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  • How to insert into std::map.

    - by Knowing me knowing you
    In code below: map<string,vector<int>> create(ifstream& in, const vector<string>& vec) { /*holds string and line numbers into which each string appears*/ typedef map<string,vector<int>> myMap; typedef vector<string>::const_iterator const_iter; myMap result; string tmp; unsigned int lineCounter = 0; while(std::getline(in,tmp)) { const_iter beg = vec.begin(); const_iter end = vec.end(); while (beg < end) { if ( tmp.find(*beg) != string::npos) { result[*beg].push_back(lineCounter);//THIS IS THE LINE I'M ASKING FOR } ++beg; } ++lineCounter; } return result; } How should I do it (check line commented in code) if I want to use insert method of map instead of using operator[]? Thank you.

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  • How to declare a pointer to a variable as a parameter of a function in C++?

    - by Keand64
    I have a function that takes a pointer to a D3DXVECTOR3, but I have no reason to declare this beforehand. The most logical solution to me was using new: Function( //other parameters, new D3DXVECTOR3(x, y, 0)); but I don't know how I would go about deleting it, beign intitialized in a function. My next thought was to use the & operator, like so: Function( //other parameters, &D3DVECTOR3(x, y, 0)); but I don't know if this is a valid way to go about doing this. (It doesn't get an error, but neither does int *x; x = 50;). So should I use new, &, or some other technique I'm overlooking?

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