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  • Initializing structs in C++

    - by Neil Butterworth
    As an addendum to this question, what is going on here: #include <string> using namespace std; struct A { string s; }; int main() { A a = {0}; } Obviously, you can't set a std::string to zero. Can someone provide an explanation (backed with references to the C++ Standard, please) about what is actually supposed to happen here? And then explain for example): int main() { A a = {42}; } Are either of these well-defined? Once again an embarrassing question for me - I always give my structs constructors, so the issue has never arisen before.

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  • standard rectangle class

    - by Neil G
    I have a project that has a GUI (written in QT) and a command-line version. I made use of the rectangle class included in QT: QRect. I would like to break the command-line version's dependency on QT, so I need a drop-in rectangle class that supports intersection and union. I could write one, but I'd prefer including one if possible. Any ideas?

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  • Is re-using a Command and Connection object in ado.net a legitimate way of reducing new object creat

    - by Neil Trodden
    The current way our application is written, involves creating a new connection and command object in every method that access our sqlite db. Considering we need it to run on a WM5 device, that is leading to hideous performance. Our plan is to use just one connection object per-thread but it's also occurred to us to use one global command object per-thread too. The benefit of this is it reduces the overhead on the garbage collector created by instantiating objects all over the place. I can't find any advice against doing this but wondered if anyone can answer definitively if this is a good or bad thing to do, and why?

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  • Static vs Non Static constructors

    - by Neil N
    I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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  • Formatting Dates in Rails 3.0

    - by Neil Middleton
    I'm trying to format a date in Rails 3 using the new syntax as described in the code: http://github.com/rails/rails/blob/master/activesupport/lib/active_support/core_ext/date/conversions.rb by using the following syntax in an initialiser: Date::DATE_FORMATS[:my_format] = '%m %d %Y' I am then referencing dates in my view like so: comment.created_at.to_formatted_s(:my_format) However, I'm just getting the default formatting - what could be wrong?

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  • PHP - preg_replace with multiple matches

    - by Neil
    Let's say I have a string like: $text = "<object>item_id1a2b3</object>xxx<object>item_id4c5d6</object>" I want to convert it to: %ITEM:1a2b3xxx%ITEM:4c5d6 Here's what I've got: $text = preg_replace("/<object.*item_id([a-zA-Z0-9]+).*<\/object/","%ITEM:$1",$text); This isn't quite right, as the search is greedy. Thoughts? Thanks!

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  • Esoteric C++ operators

    - by Neil G
    What is the purpose of the following esoteric C++ operators? Pointer to member ::* Bind pointer to member by pointer ->* Bind pointer to member by reference .* (reference)

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  • Initial capacity of collection types, i.e. Dictionary, List

    - by Neil N
    Certain collection types in .Net have an optional "Initial Capacity" constructor param. i.e. Dictionary<string, string> something = new Dictionary<string,string>(20); List<string> anything = new List<string>(50); I can't seem to find what the default initial capacity is for these objects on MSDN. If I know I will only be storing 12 or so items in a dictionary, doesn't it make sense to set the initial capacity to something like 20? My reasoning is, assuming the capacity grows like it does for a StringBuiler, which doubles each time the capacity is hit, and each re-allocation is costly, why not pre-set the size to something you know will hold your data, with some extra room just in case? If the initial capacity is 100, and I know I will only need a dozen or so, it seems as though the rest of that allocated RAM is allocated for nothing. Please spare me the "premature optimization" speil for the O(n^n)th time. I know it won't make my apps any faster or save any meaningful amount of memory, this is mostly out of curiosity.

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  • functional, bind1st and mem_fun

    - by Neil G
    Why won't this compile? #include <functional> #include <boost/function.hpp> class A { A() { typedef boost::function<void ()> FunctionCall; FunctionCall f = std::bind1st(std::mem_fun(&A::process), this); } void process() {} }; Errors: In file included from /opt/local/include/gcc44/c++/bits/stl_function.h:712, from /opt/local/include/gcc44/c++/functional:50, from a.cc:1: /opt/local/include/gcc44/c++/backward/binders.h: In instantiation of 'std::binder1st<std::mem_fun_t<void, A> >': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:100: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:103: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:106: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:111: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:117: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h: In function 'std::binder1st<_Operation> std::bind1st(const _Operation&, const _Tp&) [with _Operation = std::mem_fun_t<void, A>, _Tp = A*]': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:126: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' In file included from /opt/local/include/boost/function/detail/maybe_include.hpp:13, from /opt/local/include/boost/function/detail/function_iterate.hpp:14, from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47, from /opt/local/include/boost/function.hpp:64, from a.cc:2: /opt/local/include/boost/function/function_template.hpp: In static member function 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::binder1st<std::mem_fun_t<void, A> >, R = void]': /opt/local/include/boost/function/function_template.hpp:913: instantiated from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:722: instantiated from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:1064: instantiated from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' a.cc:7: instantiated from here /opt/local/include/boost/function/function_template.hpp:153: error: no match for call to '(std::binder1st<std::mem_fun_t<void, A> >) ()'

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  • What is the difference between causal models and directed graphical models?

    - by Neil G
    What is the difference between causal models and directed graphical models? or: What is the difference between causal relationships and directed probabilistic relationships? or, even better: What would you put in the interface of a DirectedProbabilisticModel class, and what in a CausalModel class? Would one inherit from the other? Collaborative solution: interface DirectedModel { map<Node, double> InferredProbabilities(map<Node, double> observed_probabilities, set<Node> nodes_of_interest) } interface CausalModel: DirectedModel { bool NodesDependent(set<Node> nodes, map<Node, double> context) map<Node, double> InferredProbabilities(map<Node, double> observed_probabilities, map<Node, double> externally_forced_probabilities, set<Node> nodes_of_interest) }

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  • Validating a value for a DataColumn

    - by Richard Neil Ilagan
    Hello! I'm using a DataGrid with edit functionalities in my project. It's handy, compared to having to edit its source data manually, but sadly, that means that I'll have to deal with validating user input a bit more. And my problem is basically just that. When I set my DataGrid to EDIT mode, modify the values and then set it to UPDATE, what is the best way to check if a value that I've entered is, in fact, compatible with the corresponding column's data type? i.e. (simple example) // assuming DataTable dt = new DataTable(); dt.Columns.Add("aa",typeof(System.Int32)); DataGrid dg = new DataGrid(); dg.DataSource = dt; dg.DataBind(); dg.UpdateCommand += dg_Update; // this is the update handler protected void dg_Update(object src, DataGridCommandEventArgs e) { string newValue = (someValueIEnteredInTextBox); // HOW DO I CHECK IF [newValue] IS COMPATIBLE WITH COLUMN "aa" ABOVE? dt.LoadDataRow(newValue, true); } Thanks guys. Any leads would be so much help.

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  • asp:Button is not calling server-side function

    - by Richard Neil Ilagan
    Hi guys, I know that there has been much discussion here about this topic, but none of the threads I got across helped me solve this problem. I'm hoping that mine is somewhat unique, and may actually merit a different solution. I'm instantiating an asp:Button inside a data-bound asp:GridView through template fields. Some of the buttons are supposed to call a server-side function, but for some weird reason, it doesn't. All the buttons do when you click them is fire a postback to the current page, doing nothing, effectively just reloading the page. Below is a fragment of the code: <asp:GridView ID="gv" runat="server" AutoGenerateColumns="false" CssClass="l2 submissions" ShowHeader="false"> <Columns> <asp:TemplateField> <ItemTemplate><asp:Panel ID="swatchpanel" CssClass='<%# Bind("status") %>' runat="server"></asp:Panel></ItemTemplate> <ItemStyle Width="50px" CssClass="sw" /> </asp:TemplateField> <asp:BoundField DataField="description" ReadOnly="true"> </asp:BoundField> <asp:BoundField DataField="owner" ReadOnly="true"> <ItemStyle Font-Italic="true" /> </asp:BoundField> <asp:BoundField DataField="last-modified" ReadOnly="true"> <ItemStyle Width="100px" /> </asp:BoundField> <asp:TemplateField> <ItemTemplate> <asp:Button ID="viewBtn" cssclass='<%# Bind("sid") %>' runat="server" Text="View" OnClick="viewBtnClick" /> </ItemTemplate> </asp:TemplateField> </Columns> </asp:GridView> The viewBtn above should call the viewBtnClick() function on server-side. I do have that function defined, along with a proper signature (object,EventArgs). One thing that may be of note is that this code is actually inside an ASCX, which is loaded in another ASCX, finally loaded into an ASPX. Any help or insight into the matter will be SO appreciated. Thanks! (oh, and please don't mind my trashy HTML/CSS semantics - this is still in a very,very early stage :p)

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  • Using a Type object to create a generic

    - by Richard Neil Ilagan
    Hello all! I'm trying to create an instance of a generic class using a Type object. Basically, I'll have a collection of objects of varying types at runtime, and since there's no way for sure to know what types they exactly will be, I'm thinking that I'll have to use Reflection. I was working on something like: Type elType = Type.GetType(obj); Type genType = typeof(GenericType<>).MakeGenericType(elType); object obj = Activator.CreateInstance(genType); Which is well and good. ^_^ The problem is, I'd like to access a method of my GenericType< instance, which I can't because it's typed as an object class. I can't find a way to cast it obj into the specific GenericType<, because that was the problem in the first place (i.e., I just can't put in something like:) ((GenericType<elType>)obj).MyMethod(); How should one go about tackling this problem? Many thanks! ^_^

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  • Extract multiple values from one column in MySql

    - by Neil
    I've noticed that MySql has an extensive search capacity, allowing both wildcards and regular expressions. However, I'm in somewhat in a bind since I'm trying to extract multiple values from a single string in my select query. For example, if I had the text "<span>Test</span> this <span>query</span>", perhaps using regular expressions I could find and extract values "Test" or "query", but in my case, I have potentially n such strings to extract. And since I can't define n columns in my select statement, that means I'm stuck. Is there anyway I could have a list of values (ideally separated by commas) of any text contained with span tags? In other words, if I ran this query, I would get "Test,query" as the value of spanlist: select <insert logic here> as spanlist from HtmlPages ...

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  • how to tackle a custom forms database

    - by Neil Hickman
    I'm currently researching a project for the place that I work in. We are trying to create a system that will allow forms to be set up dynamically from a database. My question is what database structure would best suit something like this? I currently have a structure of: forms_form forms_formfields forms_formdata I don't think this is the most appropriate layout for this. Basically to make is make sense I need to be able to make a form within the database that can have infinite fields all customized and have the data when submitted stored in the database.

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  • asp:Validator in invisible elements + invisible targets

    - by Richard Neil Ilagan
    Somewhat straightforward: will asp:Validators still perform validation when they're in invisible containers? How about if their ControlToValidate target is invisible? For example: <asp:Panel id="myPanel" runat="server" visible="false"> <asp:Textbox id="myTextbox" runat="server" /> <asp:RequiredFieldValidator id="myRfv" runat="server" controltovalidate="myTextbox" /> </asp:Panel> Above is a Validator in an invisible Panel. Would myRfv still perform validation? How about if myTextbox is invisible instead? I'm asking this because I have very specialized Validators in my ASPX, wherein I also have Panels which are hidden/shown dynamically. While I'm all for disabling the validators themselves, I'm just curious whether they'll automatically disable anyway. Thanks guys! :D

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  • decltype, result_of, or typeof?

    - by Neil G
    I have: class A { public: B toCPD() const; And: template<typename T> class Ev { public: typedef result_of(T::toCPD()) D; After instantiating Ev<A>, the compiler says: meta.h:12: error: 'T::toCPD' is not a type neither decltype nor typeof work either.

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  • In CMake, how does CHECK_INCLUDE_FILE_CXX work?

    - by Neil G
    The following code prints nothing CHECK_INCLUDE_FILE_CXX(glog/logging.h GLOG_INCLUDE) IF(GLOG_INCLUDE) MESSAGE("YY") ENDIF(GLOG_INCLUDE) But I have the following environment variable set: export CPLUS_INCLUDE_PATH=/usr/local/include And, "ls /usr/local/include/glog/logging.h" returns the file. I tried using include_directories( "/usr/local/include" ) but it doesn't work either.

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  • Ubuntu quickly (python/gtk) - how to monitor stdin?

    - by neil
    I'm starting to work with Ubuntu's "quickly" framework, which is python/gtk based. I want to write a gui wrapper for a textmode C state-machine that uses stdin/stdout. I'm new to gtk. I can see that the python print command will write to the terminal window, so I assume I could redirect that to my C program's stdin. But how can I get my quickly program to monitor stdin (i.e. watch for the C program's stdout responses)? I suppose I need some sort of polling loop, but I don't know if/where that is supported within the "quickly" framework. Or is redirection not the way to go - should I be looking at something like gobject.spawn_async?

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  • MySql TABLE data type

    - by Neil Aitken
    MS SQL Server has a TABLE data type which can be used in stored procedures, Does anybody know if MySQL has an equivalent data type? I've had a look over the docs but can't seem to find anything, so I presume it doesn't exist, but perhaps somebody has created a workaround

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  • Initialising structs in C++

    - by Neil Butterworth
    As an addendum to this question, what is going on here: #include <string> using namespace std; struct A { string s; }; int main() { A a = {0}; } Obviously, you can't set a std::string to zero. Can someone provide an explanation (backed with references to the C++ Standard, please) about what is actually supposed to happen here? And then explain for example): int main() { A a = {42}; } Are either of these well-defined? Once again an embarrassing question for me - I always give my structs constructors, so the issue has never arisen before.

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  • How often do you implement the big three?

    - by Neil Butterworth
    I was just musing about the number of questions here that either are about the "big three" (copy constructor, assignment operator and destructor) or about problems caused by them not being implemented correctly, when it occurred to me that I could not remember the last time I had implemented them myself. A swift grep on my two most active projects indicate that I implement all three in only one class out of about 150. That's not to say I don't implement/declare one or more of them - obviously base classes need a virtual destructor, and a large number of my classes forbid copying using the private copy ctor & assignment op idiom. But fully implemented, there is this single lonely class, which does some reference counting. So I was wondering am I unusual in this? How often do you implement all three of these functions? Is there any pattern to the classes where you do implement them?

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