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  • how to avoid temporaries when copying weakly typed object

    - by Truncheon
    Hi. I'm writing a series classes that inherit from a base class using virtual. They are INT, FLOAT and STRING objects that I want to use in a scripting language. I'm trying to implement weak typing, but I don't want STRING objects to return copies of themselves when used in the following way (instead I would prefer to have a reference returned which can be used in copying): a = "hello "; b = "world"; c = a + b; I have written the following code as a mock example: #include <iostream> #include <string> #include <cstdio> #include <cstdlib> std::string dummy("<int object cannot return string reference>"); struct BaseImpl { virtual bool is_string() = 0; virtual int get_int() = 0; virtual std::string get_string_copy() = 0; virtual std::string const& get_string_ref() = 0; }; struct INT : BaseImpl { int value; INT(int i = 0) : value(i) { std::cout << "constructor called\n"; } INT(BaseImpl& that) : value(that.get_int()) { std::cout << "copy constructor called\n"; } bool is_string() { return false; } int get_int() { return value; } std::string get_string_copy() { char buf[33]; sprintf(buf, "%i", value); return buf; } std::string const& get_string_ref() { return dummy; } }; struct STRING : BaseImpl { std::string value; STRING(std::string s = "") : value(s) { std::cout << "constructor called\n"; } STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } bool is_string() { return true; } int get_int() { return atoi(value.c_str()); } std::string get_string_copy() { return value; } std::string const& get_string_ref() { return value; } }; struct Base { BaseImpl* impl; Base(BaseImpl* p = 0) : impl(p) {} ~Base() { delete impl; } }; int main() { Base b1(new INT(1)); Base b2(new STRING("Hello world")); Base b3(new INT(*b1.impl)); Base b4(new STRING(*b2.impl)); std::cout << "\n"; std::cout << b1.impl->get_int() << "\n"; std::cout << b2.impl->get_int() << "\n"; std::cout << b3.impl->get_int() << "\n"; std::cout << b4.impl->get_int() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_ref() << "\n"; std::cout << b2.impl->get_string_ref() << "\n"; std::cout << b3.impl->get_string_ref() << "\n"; std::cout << b4.impl->get_string_ref() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_copy() << "\n"; std::cout << b2.impl->get_string_copy() << "\n"; std::cout << b3.impl->get_string_copy() << "\n"; std::cout << b4.impl->get_string_copy() << "\n"; return 0; } It was necessary to add an if check in the STRING class to determine whether its safe to request a reference instead of a copy: Script code: a = "test"; b = a; c = 1; d = "" + c; /* not safe to request reference by standard */ C++ code: STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } If was hoping there's a way of moving that if check into compile time, rather than run time.

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  • How to properly assign a value to the member of a struct that has a class data type?

    - by sasayins
    Hi, Please kindly see below for the codes. Its compiling successfully but the expected result is not working. Im very confused because my initialization of the array is valid, //cbar.h class CBar { public: class CFoo { public: CFoo( int v ) : m_val = v {} int GetVal() { return m_val; } private: int m_val; }; public: static const CFoo foo1; static const CFoo foo2; public: CBar( CFoo foo ) m_barval( foo.GetVal() ){} int GetFooVal() { return m_barval; } private: int m_barval; }; //cbar.cpp const CBar::CFoo foo1 = CBar::CFoo(2); const CBar::CFoo foo2 = CBar::CFoo(3); //main.cpp struct St { CBar::CFoo foo; }; St st[] = { CBar::foo1, CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } But then when I change the St::foo to a pointer. And like assign the address of CBar::foo1 or CBar::foo2, its working, like this, //main.cpp struct St { const CBar::CFoo *foo; }; St st[] = { &CBar::foo1, &CBar::foo2 }; for( int i=0; i<sizeof(st)/sizeof(St); i++ ) { CBar cbar( *st[i].foo ); std::cout << cbar.GetFooVal() << std::endl; } The real problem is. The app should output 2 3 Please advice. Many thanks.

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  • How to increment a value using a C-Preprocessor?

    - by mystify
    Example: I try to do this: static NSInteger stepNum = 1; #define METHODNAME(i) -(void)step##i #define STEP METHODNAME(stepNum++) @implementation Test STEP { // do stuff... [self nextFrame:@selector(step2) afterDelay:1]; } STEP { // do stuff... [self nextFrame:@selector(step3) afterDelay:1]; } STEP { // do stuff... [self nextFrame:@selector(step4) afterDelay:1]; } // ... When building, Xcode complains that it can't increment stepNum. This seems logical to me, because at this time the code is not "alive" and this pre-processing substitution stuff happens before actually compiling the source code. Is there another way I could have an variable be incremented on every usage of STEP macro, the easy way?

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  • How to write function where argument is type but not typed value?

    - by ssp
    I want to convert a string representations of few dozen enum types to enum values. It's easy to convert string to concrete type: Enum.Parse(typeof<FontStyle>,"Bold") |> unbox<FontStyle> but for now i want to write function where type and string are parameters. The best one i can write is: > let s2e (_: 'a) s = Enum.Parse(typeof<'a>,s) |> unbox<'a>;; val s2e : 'a -> string -> 'a > s2e FontStyle.Regular "Bold";; val it : FontStyle = Bold Is there any option to write something like this but with type itself as first argument?

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  • Is it possible to use an incremental value within a variable name whilst declaring it within a loop?

    - by Jack
    Hi, I'm creating function which will read different XML files each time that will contain different amounts of the same nodes. I have already created a loop which stores the ID of each node into an array, and now I want to create variables for each array member which store attributes of the node with each ID. Because the number of nodes will be different for every XML document my function reads, I cannot manually assign variables for the attributes of each node ID not knowing how many to assign, so I have created a loop which runs specific to the number of items I have stored in the array. Inside this loop I was hoping to have something like: for (i=0; i<array.length; i++) { var ID + i + width = exampleheight var ID + i + height = exampleheight } I know this doesn't work, but was trying to outline what I am looking to find out. Is it possible to use some kind of variable or random number when declaring a variable?

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  • transforming flat php array into multidimensional one based on key value?

    - by PopRocks4344
    I have a flat array that I'm trying to make multidimensional. Basically, I want to find the items that have parents and create a subarray for that parent id. Right now (and this is simplified), it looks like this: Array ( [0] => stdClass Object ( [id] => 1 [parent] => 0 [name ] => Parent1 ) [1] => stdClass Object ( [id] => 7 [parent] => 1 [name] => Child1 ) [2] => stdClass Object ( [id] => 9 [parent] => 1 [name] => Child2 ) [3] => stdClass Object ( [id] => 2 [parent] => 0 [name ] => Parent2 ) [4] => stdClass Object ( [id] => 88 [parent] => 2 [name] => Childof2 ) ) I'm trying to make this: Array ( [0] => stdClass Object ( [id] => 1 [parent] => 0 [name ] => Parent1 [children] => stdClass Object ( [1] => stdClass Object ( [id] => 7 [parent] => 1 [name] => Child1 ) [2] => stdClass Object ( [id] => 9 [parent] => 1 [name] => Child2 ) ) ) [1] => stdClass Object ( [id] => 2 [parent] => 0 [name ] => Parent2 [children] => stdClass Object ( [0] => stdClass Object ( [id] => 88 [parent] => 2 [name] => Childof2 ) ) ) )

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  • How to break out of a loop depending on a CheckBox Checked value while the loop is running?

    - by Rayner Vaz
    Lets say I want to call a function repeatedly if the user selects a CheckBox named "repeat" but the calls to the function should stop as soon as the user 'unchecks' the CheckBox. I tried using the 'Checked', 'Click' and 'Tap' event of the CheckBox but once the loop starts, it does not sense any changes in the checkbox's state. I even tried using a loop inside another button's _Click method, but then that creates a lock on the Button's 'pressed' state. Any ideas/alternate suggestions?

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  • A way to share the return value of fsockopen() between multiple pages?

    - by Chilln
    Hey, im using a connection to a server in my php script, opened with fsockopen() and i want it to share between different pages so i serialized it and saved it in a session variable but it seems that that ia a bad idea because when i do this nothing happens... Not even an error. The problem is that this connection requires a handshake so i cant reconnect everytime Another question, whats the timeout of fsockopen or does the connection stay alive if the. original php script which called it is closed?

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  • How to prevent CAST errors on SSIS ?

    - by manitra
    Hello, The question Is it possible to ask SSIS to cast a value and return NULL in case the cast is not allowed instead of throwing an error ? My environment I'm using Visual Studio 2005 and Sql Server 2005 on Windows Server 2003. The general context Just in case you're curious, here is my use case. I have to store data coming from somewhere in a generic table (key/value structure with history) witch contains some sort of value that can be strings, numbers or dates. The structure is something like this : table Values { Id int, Date datetime, -- for history Key nvarchar(50) not null, Value nvarchar(50), DateValue datetime, NumberValue numeric(19,9) } I want to put the raw value in the Value column and try to put the same value in the DateValue column when i'm able to cast it to Datetime in the NumberValue column when i'm able to cast it to a number Those two typed columns would make all sort of aggregation and manipulation much easier and faster later. That's it, now you know why i'm asking this strange question. ============ Thanks in advance for your help.

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  • not getting hidden values while postback of a button in.net

    - by user1075242
    I am using asp.net. I have taken one Hidden value and assigning value to that hidden variable in Java-script. aspx: <input type="hidden" runat="server" id="hdnProductionIds" value="0" name="hdnProductionIds" /> JS: document.getElementById("ctl00_ContentPlaceHolder1_hdnProductionIds").value = "123"; I want to use that hidden value in server side coding(vb.net). But while do-post back, hidden variable value becomes Zero (default value) Can any one please suggest me. Thanks, Jagadi.

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  • How can I use a value of JSP in Javascript code?

    - by novellino
    Hello, I have a list of elements, each of them appeared in my page through jsp. So I have this: <div id="title"><%= list.get(ind).getTitle() %></div> When I display the elements, as this tag is in for loop, I get everything right. Now I what to place a button for deleting each of this elements. What I have done is: <input type="submit" name="submit" onclick="deleteNewsFunction();" id="submit_btn"/> In the deleteNewsFunction() I just want to print the data. <script> function deleteNewsFunction(){ var item = $('#title').val(); alert(item); } </script> The problem is that the title var gets always the first item even if I am clicking on the button of the second item. I was thinking that maybe a solution is to add the "list.get(ind).getTitle()" as a parameter in the function like deleteNewsFunction(<%=list.get(ind).getTitle()%) but then it did not work at all. Does anyone know how to help me? Thanks a lot!

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  • What is a good solution to link different tables in Hibernate based on some field value?

    - by serg555
    I have article table and several user tables a_user, b_user, ... with exactly the same structure (but different data). I can't change anything in *_user tables except their table name prefix but can change everything else (user tables contain only user information, there is nothing about article or user_type in them). I need to link article to a user (many-to-one), but user table name is defined by user_type field. For example Article table record: ... user_id="5" user_type="a" means that it is linked to a user with id=5 from a_user table (id 5 is not unique in users scope, each user table can have its id 5). Any suggestions how to handle this situation? How can I map this relation in Hibernate (xml mapping, no annotations) so it will automatically pick up correct user for an article during select/update? How should I map user tables (one or multiple classes?)? I would need to run some queries like this: from Article a where a.userType=:type and a.user.name=:name Thanks.

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  • How do I access a value of a nested Perl hash?

    - by st
    I am new to Perl and I have a problem that's very simple but I cannot find the answer when consulting my Perl book. When printing the result of Dumper($request); I get the following result: $VAR1 = bless( { '_protocol' => 'HTTP/1.1', '_content' => '', '_uri' => bless( do{\(my $o = 'http://myawesomeserver.org:8081/counter/')}, 'URI::http' ), '_headers' => bless( { 'user-agent' => 'Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.4) Gecko/20080528 Epiphany/2.22 Firefox/3.0', 'connection' => 'keep-alive', 'cache-control' => 'max-age=0', 'keep-alive' => '300', 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'accept-language' => 'en-us,en;q=0.5', 'accept-encoding' => 'gzip,deflate', 'host' => 'localhost:8081', 'accept-charset' => 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' }, 'HTTP::Headers' ), '_method' => 'GET', '_handle' => bless( \*Symbol::GEN0, 'FileHandle' ) }, 'HTTP::Server::Simple::Dispatched::Request' ); How can I access the values of '_method' ('GET') or of 'host' ('localhost:8081'). I know that's an easy question, but Perl is somewhat cryptic at the beginning.

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  • how do I copy value from one table and inserted to another in the same database??

    - by mathew
    I am having a tough time to do this... I have created two table say table-1 and table-2 in same database.what I want is I need to copy some values from table-1 and insert the same to table-2. I have tried many ways but it does not seems work. below is my code can any one tell me where I am missing?? $db = mysql_connect("localhost", "user", "pass") or die("Could not connect."); mysql_select_db("comdata",$db)or die(mysql_error()); $resultb = mysql_query("SELECT * FROM table-2")or die(mysql_error()); $row = mysql_fetch_array($resultb); $days = (strtotime(date("Y-m-d")) - strtotime($row['regtime'])) / (60 * 60 * 24); if($row > 0 && $days < 1){ $person = $row['person']; $catogr = $row['catog']; $position = $row['position']; $location = $row['location']; $rank = $row['rank']; mysql_close($db); }else{ $db = mysql_connect("localhost", "user", "pass") or die("Could not connect."); mysql_select_db("comdata",$db)or die(mysql_error()); $result = mysql_query("SELECT * FROM table-1 WHERE regtime = DATE(NOW()) ORDER BY rank ASC LIMIT 1;")or die(mysql_error()); $row = mysql_fetch_array($result); $person = $row['person']; $catogr = $row['catog']; $position = $row['position']; $location = $row['location']; $rank = $row['rank']; mysql_query("INSERT INTO table-2 (regtime,person,catog,position,location,rank) VALUES(NOW(),'$person','$catogr','$position','$location','$rank')"); mysql_close($db); }

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  • How to disable the mediaplayer cookies

    - by Geetha
    Hi All, How to disable the mediaplayers cookies. Is there any parameter for that? Code: <object id="mediaPlayer" classid="clsid:22D6F312-B0F6-11D0-94AB-0080C74C7E95" codebase="http://activex.microsoft.com/activex/controls/mplayer/en/nsmp2inf.cab#Version=5,1,52,701" height="1" standby="Loading Microsoft Windows Media Player components..." type="application/x-oleobject" width="1"> <param name="fileName" value="" /> <param name="animationatStart" value="true" /> <param name="transparentatStart" value="true" /> <param name="autoStart" value="true" /> <param name="showControls" value="true" /> <param name="volume" value="100" /> <param name="loop" value="false" /> </object>

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  • How to write a value validation method for core data?

    - by mystify
    The docs say: you should implement methods of the form validate:error:, as defined by the NSKeyValueCoding protocol so lets say I have an attribute which is an int: friendAge I want to make sure that any friend may not be younger than 30. So how would I make that validation method? -validateFriendAge:error: What am I gonna do in there, exactly? And what shall I do with that NSError I get passed? I think it has an dictionary where I can return a humanly readable string in an arbitrary language (i.e. the one that's used currently), so I can output a reasonable error like: "Friend is not old enough"... how to do that?

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  • Is passing a struct value to a method by-reference in C# an acceptable optimization?

    - by Arc
    Say I have a struct: struct MyStruct { public int X public int Y } And a method in some class that is iterated over many times elsewhere: public bool MyMethod( MyStruct myStruct ) { return ... } Is changing the MyMethod signature to the following an acceptable optimization? public bool MyMethod( ref MyStruct myStruct ) If so, how much of an advantage would it really be? If not, about how many fields would a struct need for a big enough advantage using ref this way?

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