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• Function Composition in C++

  - by Channel72

  There are a lot of impressive Boost libraries such as Boost.Lambda or Boost.Phoenix which go a long way towards making C++ into a truly functional language. But is there a straightforward way to create a composite function from any 2 or more arbitrary functions or functors? If I have: int f(int x) and int g(int x), I want to do something like f . g which would statically generate a new function object equivalent to f(g(x)). This seems to be possible through various techniques, such as those discussed here. Certainly, you can chain calls to boost::lambda::bind to create a composite functor. But is there anything in Boost which easily allows you to take any 2 or more functions or function objects and combine them to create a single composite functor, similar to how you would do it in a language like Haskell?

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• Identifying a function call in a python script line in runtime

  - by Dani

  I have a python script that I run with 'exec'. The script's string has calls to functions. When a function is called, I would like it to know the line number and offset in line for that call in the script (in the string I fed exec with). Here is an example. If my script is: foo1(); foo2(); foo1() foo3() And if I have code that prints (line,offset) in every function, I should get (0,0), (0,8), (0,16), (1,0) In most cases this can be easily done by getting the stack frame, because it contains the line number and the function name. The only problem is when there are two functions with the same name in a certain line. Unfortunately this is a common case for me. Any ideas?

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• C++ inheritance and member function pointers

  - by smh

  In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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• Is there any performance issue using Row_Number to implement table paging in Sql Server 2008?

  - by majkinetor

  I want to implement table paging using this method: SET @PageNum = 2; SET @PageSize = 10; WITH OrdersRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY OrderDate, OrderID) AS RowNum ,* FROM dbo.Orders ) SELECT * FROM OrdersRN WHERE RowNum BETWEEN (@PageNum - 1) * @PageSize + 1 AND @PageNum * @PageSize ORDER BY OrderDate ,OrderID; Is there anything I should be aware of ? Table has millions of records. Thx. EDIT: After using suggested MAXROWS method for some time (which works really really fast) I had to switch back to ROW_NUMBER method because of its greater flexibility. I am also very happy about its speed so far (I am working with View having more then 1M records with 10 columns). To use any kind of query I use following modification: PROCEDURE [dbo].[PageSelect] ( @Sql nvarchar(512), @OrderBy nvarchar(128) = 'Id', @PageNum int = 1, @PageSize int = 0 ) AS BEGIN SET NOCOUNT ON Declare @tsql as nvarchar(1024) Declare @i int, @j int if (@PageSize <= 0) OR (@PageSize > 10000) SET @PageSize = 10000 -- never return more then 10K records SET @i = (@PageNum - 1) * @PageSize + 1 SET @j = @PageNum * @PageSize SET @tsql = 'WITH MyTableOrViewRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY ' + @OrderBy + ') AS RowNum ,* FROM MyTableOrView WHERE ' + @Sql + ' ) SELECT * FROM MyTableOrViewRN WHERE RowNum BETWEEN ' + CAST(@i as varchar) + ' AND ' + cast(@j as varchar) exec(@tsql) END If you use this procedure make sure u prevented sql injection.

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• c++ exercise question

  - by Djecua

  in need of help on a C++ program that will help a deli owner help her customers.Prompt the user for the number of bagels.if then calculate the customers payment two ways. first it finds the price of the smallest multiple of 13 bagels that is closet to the customer's order. it then calculates the price of the customer's order so that the customer's payment is the smallest amount possible with the customer getting the exact number of bagels ordered. if the first method is the smallest amount the program outputs the number of bagels the customer will receive along with the dollar amount owed and the dollar amount saved. otherwise just print the number of bagels received the dollar amount owed $ 3.80 for a dozen bagels (13 bagels) half a dozen(6 bagels) sing bagel cost $.50 owner of the deli is a honest merchant, customers always get the best price on an order, even if they get more bagels than ordered, for example a customer that orders 10 bagels would pay $ 4.60 (2.60 for a half dozen bagels plus $2.00 for 4 single bagels.merchant gives her customer 13 bagels saving the customer $0.80 If someone can example to me how would i design to give customer extra bagels and how to calculate cost.

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• Opinions regarding C++ programming practice

  - by Sagar

  I have a program that I am writing, not too big. Apart from the main function, it has about 15 other functions that called for various tasks at various times. The code works just fine all in one file, and as it is right now. However, I was wondering if anyone had any advice on whether it is smarter/more efficient/better programming to put those functions in a separate file different from where main is, or whether it even matters at all. If yes, why? If no, why not? I am not new at C++, but definitely not an expert either, so if you think this question is stupid, feel free to tell me so. Thanks for your time!

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• Efficient way to maintain a sorted list of access counts in Python

  - by David

  Let's say I have a list of objects. (All together now: "I have a list of objects.") In the web application I'm writing, each time a request comes in, I pick out up to one of these objects according to unspecified criteria and use it to handle the request. Basically like this: def handle_request(req): for h in handlers: if h.handles(req): return h return None Assuming the order of the objects in the list is unimportant, I can cut down on unnecessary iterations by keeping the list sorted such that the most frequently used (or perhaps most recently used) objects are at the front. I know this isn't something to be concerned about - it'll make only a miniscule, undetectable difference in the app's execution time - but debugging the rest of the code is driving me crazy and I need a distraction :) so I'm asking out of curiosity: what is the most efficient way to maintain the list in sorted order, descending, by the number of times each handler is chosen? The obvious solution is to make handlers a list of (count, handler) pairs, and each time a handler is chosen, increment the count and resort the list. def handle_request(req): for h in handlers[:]: if h[1].handles(req): h[0] += 1 handlers.sort(reverse=True) return h[1] return None But since there's only ever going to be at most one element out of order, and I know which one it is, it seems like some sort of optimization should be possible. Is there something in the standard library, perhaps, that is especially well-suited to this task? Or some other data structure? (Even if it's not implemented in Python) Or should/could I be doing something completely different?

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• code folding in Visual Studio for F#

  - by Yin Zhu

  I find that I tend to write long source files in F#. Some open source projects in F# also have long source files, e.g. FPersec and F# for excel. So it would be very helpful if code folding (even very limited support) is available in VS for F#. E.g. in a module, we can fold out functions that are stable, only leave functions that are subject to change unfold. Is this feature easy to be supported, e.g. by a third party vendor?

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• Django, javascript and code ruse problem

  - by dragoon

  Hi, I have some sort of a design problem with my Django AJAX application. I have a template where I initialize js variable from django context variable like so: var test = "{{ test }}"; This variable is than used in a number of js functions that are needed for interface to work properly. So now I'm trying to reuse some content from this page in another page that loads it dynamically on some user interaction using jQuery.load(..), and I don't see any way how I can initialize that variable, so js functions don't work now. Is there any solution for this or may be I'm doing it wrong? Thanks.

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• Why is sqrt() not a method on Float?

  - by KaptajnKold

  In Ruby everything is an object. That's why I don't understand why we have the Math module. It seems to me that most (all?) of the functions in the Math module should have been methods on the numeric types like Integer, Float and so on. E.g. instead of Math.sqrt(5) it would make more sense to have 5.sqrt The same goes for sin, cos, tan, log10 and so on. Does anyone know why all these functions ended up in the Math module?

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• Perl: How do I extract certain bits from a byte and then covert these bits to a hex value?

  - by Siegfried Hepp

  I need to extract certain bits of a byte and covert the extract bits back to a hex value. Example (the value of the byte is 0xD2) : 76543210 bit position 11010010 is 0xD2 Bit 0-3 defines the channel which is 0010b is 0x2 Bit 4-5 defines the controller which is 01b is 0x1 Bit 6-7 defines the port which is 11b is 0x3 I somehow need to get from the byte is 0xD2 to channel is 0x2, controller is 0x1, port is 0x3 I googled allot and found the functions pack/unpack, vec and sprintf. But I'm scratching by head how to use the functions to achieve this. Any idea how to achieve this in Perl ?

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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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• How to convert from integer to unsigned char in C, given integers larger than 256?

  - by Alf_InPogform

  As part of my CS course I've been given some functions to use. One of these functions takes a pointer to unsigned chars to write some data to a file (I have to use this function, so I can't just make my own purpose built function that works differently BTW). I need to write an array of integers whose values can be up to 4095 using this function (that only takes unsigned chars). However am I right in thinking that an unsigned char can only have a max value of 256 because it is 1 byte long? I therefore need to use 4 unsigned chars for every integer? But casting doesn't seem to work with larger values for the integer. Does anyone have any idea how best to convert an array of integers to unsigned chars?

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• interactive lua prompt in opengl application

  - by anon

  Okay, so when I run lua, I get something like: lua Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio > Now, I want a prompt like this, 1) in a GUI application I've written. My GUI application can provide functions like: get_input_from_screen(); and write_this_crap_out_to_screen(); and more functions I can write as necessary I also know how to embed a lua interpreter in my C++ code (short tutorial on the web) What I don't know .. is how to connect the input/output of a lua interpreter with my GUI stuff. Any help/links apreciated. Thanks!

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• Multiple-File Template Implementation

  - by Maxpm

  With normal functions, the declaration and definition are often separated across multiple files like so: // Foo.h namespace Foo { void Bar(); } . // Foo.cpp #include "Foo.h" void Foo::Bar() { cout << "Inside function." << endl; } It is my understanding that this cannot be done with templates. The declaration and definition must not be separate because the appropriate form of the template is created "on-demand" when needed. So, how and where are templates typically defined in a multiple-file project like this? My intuition is that it would be in Foo.cpp because that's where the "meat" of functions normally is, but on the other hand it's the header file that's going to be included.

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• how to set windows 7 resolution to 16:9 in virtualbox running in ubuntu 12.04 as a host?

  - by Gabriele

  I have installed Virtualbox in Ubuntu 12.04, and I created a virtual guest with Windows 7 64bit. Guest additions were also installed. It works fine, but I can't set the resolution to anything higher than 1600 x 1200, whereas my screen is 1920x1080. Here's my system specifications: Intel(R) Core(TM) i7-3632QM CPU @ 2.20GHz AMD Radeon 7650 VGA 8 Gb RAM DDR3 Moreover, if I try to enhable 3D acceleration in the settings of my guest, when I expand to full screen it aborts... Thanks in advance Gabriele

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• Get the first and last posts in a thread

  - by Grampa

  I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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• CGridView Filter doesn't work when you add more than one button to the CButtonColumn

  - by era

  I have a CGridView as follows, <?php $this->widget('zii.widgets.grid.CGridView', array( 'id'=>'order-grid', 'dataProvider'=>$model->search(), 'filter'=>$model, 'columns'=>array( 'order_id', //'ordered_datetime', 'customer_id', 'status', //'delivery_address', array( 'class'=>'CButtonColumn', 'template' => '{view} {rollback} {receive}{pack} {dispatch}{delivered}', 'htmlOptions'=>array('width'=>'250px'), 'buttons'=>array( 'receive'=>array( 'id'=>'receive', 'name'=>'receive', 'url'=>'$this->grid->controller->createUrl("/shop/order/admin&received=true", array("id"=>$data->order_id,"asDialog"=>1,"gridId"=>$this->grid->id))', 'type'=>'submit', 'imageUrl'=>'/mdg/images/Receive1.png', 'visible'=>'($data->status=="pending")?true:false;' ), 'rollback'=>array( 'id'=>'rollback', 'name'=>'rollback', 'url'=>'$this->grid->controller->createUrl("/shop/order/admin&rollback=true", array("id"=>$data->order_id,"asDialog"=>1,"gridId"=>$this->grid->id))', 'imageUrl'=>'/mdg/images/rollback.jpg', 'visible'=>'($data->status=="pending")?false:true;' ), ), ), ), )); ? And When I add one more button to the buttons array, the filter doesnt work. Any Idea why that is? It's Great if anyone can help.. Thanks!

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• Cross-reference of computers having virtualization technology [closed]

  - by msorens

  When considering obtaining a new computer one of my prerequisites is the ability to load Windows 8 in a virtual machine (using VirtualBox). A prerequisite for that is that the host computer have virtualization technology. I located an Intel cross reference of chips having virtualization technology but I am trying to find a "higher level" cross reference between computer models and virtualization technology availability, skipping the extra step of having to first look up what CPU chip is in a machine, then cross-referencing that on Intel's list.

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• MVVM: Do I need Inheritance with ViewModels A + B ?

  - by Lisa

  Hello guys my first post on SO because EE sucks in the meantime ;P I am using wpf and mvvm in my desktop application. Scenario: I have a calendar with week A and week B which are rotating by every X week depending on the user settings. But the UserControl "week B" is only visible when the user sets the option "rotating weeks"... The UserControl with week A has a DataGrid and for week B I want to use the same UserControl of course. What I want to achieve is that all data entered/choosen by the user in the Week A is saved/backed by a ViewModel A and Model C. When the user wants a rotating weekly calendar plan I need also a ViewModel B and again Model C. The reason why I need to know what data entered by the user belongs to week A or week B is because I have to write the entered data in a certain order into the database = db.Write(weekA),db.Write(weekB),db.Write(weekA),etc... I am unsure how a solution could look like... What would you do to identify a ViewModel A or B so you know the order of how to write the data in the proper order into database? Any other suggestions are also welcome of course, maybe I think in the wrong direction its late here :) I am new to mvvm so please be patient.

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• Running exec inside function

  - by None

  How can you use the python exec keyword inside functions?

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• how to shear image in matlab without using built in function?

  - by mariam

  i want a method to shear an image without using the built in functions(methods)of the matlab, so how i can perform this?

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• How to allow all except part 1 and part 2 ?

  - by Stackfan

  This allows me to get easyly dynamic input variables instead of putting a static prefix like /en/etcetcetc, but the problem is all controllers are blocked. Everything goes to index/index. Question: How can i tell this rule allow evertying as it is now, but do not track if it contains http://site.com/donotcatch/me and http://site.com/iamnotbelongstodynamic1/blabla protected function _initRoutes() { ... $dynamic1 = new Zend_Controller_Router_Route( '/:variable0/:variable1', array( 'controller' => 'index', 'action' => 'index'), array( 'variable0' => '^[a-zA-Z0-9_]*$', 'variable1' => '^[a-zA-Z0-9_]*$', ) ); Follow up: Normally, i always belive yes we can, so, we can do that like this where dynamic1 does not the inter-fare with my other static controllers: // http://site/yeswecan/blabla // variable0 = yeswecan // variable1 = blabla $dynamic1 = new Zend_Controller_Router_Route( '/:variable0/:variable1', array( 'controller' => 'index', 'action' => 'index'), array( 'variable0' => '^[a-zA-Z]*$', 'variable1' => '^[a-z0-9_]*$', ) ); // http://site/ajax/whatever... // solves it $dynamic2 = new Zend_Controller_Router_Route( '/ajax/:variable0', array( 'controller' => 'ajax', 'action' => '' ), array( 'variable0' => '^[a-zA-Z0-9_]*$', ) ); // http://site/order/whatever... // solves it $dynamic3 = new Zend_Controller_Router_Route( '/order/:variable0', array( 'controller' => 'order', 'action' => ''), array( 'variable0' => '^[a-zA-Z0-9_]*$', ) ); Note: Still the controllers are getting failed for example http://site/ajax/whatever always goes to /ajax/index where i wanted to send it as /ajax/user-inserted-value How can i fix the $dynamic2 and $dynamic3 by keeping $dynamic1 ??

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• Seperate compilation in C++

  - by Pat Murray

  Suppose you are creating a class with multiple .cpp files (which each contain the implementation of a member function) and have the class' declaration in a .h file. Also, each .cpp file includes the .h file via the include directive. I was told that if you change the implementation of any of the member functions (.cpp files) that you will have to recompile every .cpp file in order to run the program. That is, if I had 5 member functions (each implemented in a .cpp file) and I changed the implementation of 1 of the .cpp files I would have to compile the 1 .cpp file I changed AND the 4 other .cpp files I didn't change in order to correctly run my program. My question, if the previous statement is true, is why is the statement is true? Any insight on this concept would be helpful.

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• How to extract a single function from a source file

  - by Adam Matan

  Hi, I'm working on a small academic research about extremely long and complicated functions in the Linux kernel. I'm trying to figure out if there is a good reason to write 600 or 800 lines-long functions. For that purpose, I would like to find a tool that can extract a function from a .c file, so I can run some automated tests on the function. For example, If I have the function cifs_parse_mount_options() within the file connect.c, I'm seeking a solution that would roughly work like: extract /fs/cifs/connect.c cifs_parse_mount_options and return the 523 lines of code(!) of the function, from the opening braces to the closing braces. Of course, any way of manipulating existing software packages like gcc to do that, would be most helpful too. Thanks, Udi EDIT : The answers to Regex to pull out C function prototype declarations? convinced me that matching function declaration by regex is far from trivial.

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