Search Results

Search found 2727 results on 110 pages for 'operator overloading'.

Page 93/110 | < Previous Page | 89 90 91 92 93 94 95 96 97 98 99 100  | Next Page >

• Questions to ask to ensure someone understands programming? (and iOS)

  - by Stephen J

  So, I've been tutoring my friend for 2 years. Most people learn programming on their own in 3-6 months, (sans algorithms). It's confusing 'cause he'll run anywhere I tell him to, understands how to read C and C++ honestly better than the average college student, and he'll modify and repeat anything I do... but for the love of god he doesn't move on to new things and he still has test anxiety. I've recently realized he's copied and toyed with existing, but not once gained an understanding of why. I was under the impression he was learning fast because he could write it, but when you say "Make a function that takes an NSString" and he says "How?" and I say "The same way you make ANY function that takes any parameter, NSString is just a type like int" and all I hear is "No, it's an NSString, it's a special thing." and we get into an arguing match 'cause I'm like "It's just a class like any other class, you've used them for months now" and blah... I've subconsciously avoided comprehension questions because of this. Anyway, if you have him copy a program and say "Just initialize it" "Where?" "I don't care, didLoad or initWithCoder or Awake from nib, anywhere it gets initialized" and "No, it has to be exactly where you had it!" "No it doesn't!" I'm sick of this, but he won't give up. So I'm done avoiding these yelling matches and becoming a sadist from now on. I would like some help in finding questions to ask him that force him to understand what he's doing. I'd like some help and any resources I can find. CQuestions looked like a good site, but now I need some iPhone stuff. For example: *What do properties do? How are they changed? How do you change the name of the getter? *Why are Booleans inefficent? What advantage does int have over a boolean and how does the bit-shift operator help? *What does Copy do to a string? *What's the difference between a view controller and a uiview? *Write a program from memory that displays blah on screen, and flashes each view one by one. From beginner up to intermediate, hobbyist with some algebra at most. I'm just looking for resources to work with. I left in backstory so you know to "twist" the questions so he doesn't know he's supposed to init a variable here or there, but has to figure it out, and learn why it goes "here" or that "anywhere is fine as long as it's". Sample programs, anything. I'm relatively open about this because, being a programmer, I seriously doubt he's the only one who has this issue. I'd like to know how others have overcome similar. What made things "click"? for you? Did you have a hard time finding answers on Google, and how did you learn a better way to find what you were looking for? (He's so exact, he'll search for how to write a checkers program with color X and Y inside a uiview, as his search string, instead of breaking it up into components, I need help with that too, and believe it is related). This type of problem has to remind one of us of someone they know. So, Exercises to force them to think? Ways we overcame this thing in the past? I greatly appreciate any help.

  Read the article

• What Counts For a DBA – Depth

  - by Louis Davidson

  SQL Server offers very simple interfaces to many of its features. Most people could open up SSMS, connect to a server, write a simple query and see the results. Even several of the core DBA tasks are deceptively straightforward. It doesn’t take a rocket scientist to perform a basic database backup or run a trace (even using the newfangled Extended Events!). However, appearances can be deceptive, and often times it is really important that a DBA understands not just the basics of how to perform a task, but why we do a task, and how that task works. As an analogy, consider a child walking into a darkened room. Most would know that they need to turn on the light, and how to do it, so they flick the switch. But what happens if light fails to shine forth. Most would immediately tell you that you need to consider changing the light bulb. So you hop in the car and take them to the local home store and instruct them to buy a replacement. Confronted with a 40 foot display of light bulbs, how will they decide which of the hundreds of types of bulbs, of different types, fittings, shapes, colors, power and efficiency ratings, is the right choice? Obviously the main lesson the child is going to learn this day is how to use their cell phone as a flashlight so they don’t have to ask for help the next time. Likewise, when the metaphorical toddlers who use your database server have issues, they will instinctively know something is wrong, and may even have some idea what caused it, but will have no depth of knowledge to figure out the right solution. That is where the DBA comes in and attempts to save the day. However, when one looks beneath the shiny UI, SQL Server has its own “40 foot display of light bulbs”, in the form of the tremendous number of tools and the often-bewildering amount of information they can present to the DBA, to help us find issues. Unfortunately, resorting to guesswork, to trying different “bulbs” over and over, hoping to stumble on the answer. This is where the right depth of knowledge goes a long way. If we need to write a SELECT statement, then knowing the syntax and where to find the data is not enough. Knowledge of indexes and query plans is essential. Without it, we might hit on a query that “works”, but we are basically still a user, not a programmer, because we have no real control over our platform. Is that level of knowledge deep enough? Probably not, since knowledge of the underlying metadata and structures would be very useful in helping us make sense of any query plan. Understanding the structure of an index makes the “key lookup” operator not sound like what you do when someone tapes your car key to the ceiling. So is even this level of understanding deep enough? Do we need to understand the memory architecture used to process the query? It might be a comforting level of knowledge, and will doubtless come in handy at some point, but is not strictly necessary in most cases. Beyond that lies (more or less) full knowledge of SQL language and the intricacies of every step the SQL Server engine takes to process our query. My personal theory is that, as a professional, our knowledge of a given task should extend, at a minimum, one level deeper than is strictly necessary to perform the task. Anything deeper can be left to the ridiculously smart, or obsessive, or both. As an example. tasked with storing an integer value between 0 and 99999999, it’s essential that I know that choosing an Integer over Decimal(8,0) will likely offer performance benefits. It is then useful that I also understand the value of adding a CHECK constraint, to make sure the values are valid to the desired range; and comforting that I know a little about the underlying processors, registers and computer math. Anything further, I leave to the likes of Joe Chang, whose recent blog post on the topic offers depth by the bucketful!  

  Read the article

• C# Design How to Elegantly wrap a DAL class

  - by guazz

  I have an application which uses MyGeneration's dOODads ORM to generate it's Data Access Layer. dOODad works by generating a persistance class for each table in the database. It works like so: // Load and Save Employees emps = new Employees(); if(emps.LoadByPrimaryKey(42)) { emps.LastName = "Just Got Married"; emps.Save(); } // Add a new record Employees emps = new Employees(); emps.AddNew(); emps.FirstName = "Mr."; emps.LastName = "dOOdad"; emps.Save(); // After save the identity column is already here for me. int i = emps.EmployeeID; // Dynamic Query - All Employees with 'A' in thier last name Employees emps = new Employees(); emps.Where.LastName.Value = "%A%"; emps.Where.LastName.Operator = WhereParameter.Operand.Like; emps.Query.Load(); For the above example(i.e. Employees DAL object) I would like to know what is the best method/technique to abstract some of the implementation details on my classes. I don't believe that an Employee class should have Employees(the DAL) specifics in its methods - or perhaps this is acceptable? Is it possible to implement some form of repository pattern? Bear in mind that this is a high volume, perfomacne critical application. Thanks, j

  Read the article

• Explicit casting doesn't work in default model binding

  - by Felix

  I am using ASP.NET MVC2 and Entity Framework. I am going to simplify the situation a little; hopefully it will make it clearer, not more confusing! I have a controller action to create address, and the country is a lookup table (in other words, there is a one-to-many relationship between Country and Address classes). Let's say for clarity that the field in the Address class is called Address.Land. And, for the purposes of the dropdown list, I am getting Country.CountryID and Country.Name. I am aware of Model vs. Input validation. So, if I call the dropdown field formLand - I can make it work. But if I call the field Land (that is, matching the variable in Address class) - I am getting the following error: "The parameter conversion from type 'System.String' to type 'App.Country' failed because no type converter can convert between these types." OK, this makes sense. A string (CountryID) comes from the form and the binder doesn't know how to convert it to Country type. So, I wrote the converter: namespace App { public partial class Country { public static explicit operator Country(string countryID) { AppEntities context = new AppEntities(); Country country = (Country) context.GetObjectByKey( new EntityKey("AppEntities.Countries", "CountryID", countryID)); return country; } } } FWIW, I tried both explicit and implicit. I tested it from the controller - Country c = (Country)"fr" - and it works fine. However, it never got invoked when the View is posted. I am getting the same "no type converter" error in the model. Any ideas how to hint to the model binder that there is a type converter? Thanks

  Read the article

• Verilog errors during synthesis

  - by chester.boo

  Here is the code in question: http://pastebin.com/smqUNpdt When I do a syntax check, everything is okay. But when I try to synthesize with XST I get the following errors: ERROR:Xst:870 - "fibonacci.v" line 42: Can not simplify operator DIV. ERROR:Xst:899 - "fibonacci.v" line 29: The logic for <out> does not match a known FF or Latch template. ERROR:Xst:899 - "fibonacci.v" line 30: The logic for <ratio> does not match a known FF or Latch template. ERROR:Xst:899 - "fibonacci.v" line 36: The logic for <nextstate> does not match a known FF or Latch template. ERROR:Xst:899 - "fibonacci.v" line 37: The logic for <previousstate> does not match a known FF or Latch template. ERROR:Xst:899 - "fibonacci.v" line 38: The logic for <presentstate> does not match a known FF or Latch template. ERROR:Xst:899 - "fibonacci.v" line 39: The logic for <fib_number_cnt> does not match a known FF or Latch template.

  Read the article

• Dojo Datagrid Filtering Issue

  - by Zoom Pat

  I am having hard time filtering a datagrid. Please help! This is how I draw a grid. var jsonStore = new dojo.data.ItemFileWriteStore({data:columnValues}); gridInfo = { store: jsonStore, queryOptions: {ignoreCase: true}, structure: layout }; grid = new dojox.grid.DataGrid(gridInfo, "gridNode"); grid.startup(); Now if i try something like this, it works fine and gives me the rows which has the column (AGE_FROM) value equal to 63. grid.filter({AGE_FROM:63}); but I need all kinds of filtering and not just 'equal to' So how do I try to obtain all the rows which have AGE_FROM 63, and < 63 and <= 63 and =63. because grid.filter({AGE_FROM:<63}); does not work Also One other way I was thingking was to use the following filteredStore = new dojox.jsonPath.query(filterData,"[?(@.AGE_FROM = 63]"); and then draw the grid with the filteredStore, but the above is not working for a != operator. Once I figure a good way to filter grid I need to see a way to filter out dates. I am trying to find a good example for filtering dataGrid but most of the examples are just filtering based on the 'equal to' criteria. Any help is highly appreciated.

  Read the article

• C++ question: boost::bind receive other boost::bind

  - by user355034

  I want to make this code work properly, what should I do? giving this error on the last line. what am I doing wrong? i know boost::bind need a type but i'm not getting. help class A { public: template <class Handle> void bindA(Handle h) { h(1, 2); } }; class B { public: void bindB(int number, int number2) { std::cout << "1 " << number << "2 " << number2 << std::endl; } }; template struct Wrap_ { Wrap_(Han h) : h_(h) {} template<typename Arg1, typename Arg2> void operator()(Arg1 arg1, Arg2 arg2) { h_(arg1, arg2); } Han h_; }; template inline Wrap_<Handler> make(Handler h) { return Wrap_<Handler> (h); } int main() { A a; B b; ((boost::bind)(&B::bindB, b, _1, _2))(1, 2); ((boost::bind)(&A::bindA, a, make(boost::bind(&B::bindB, b, _1, _2))))(); /i want compiled success and execute success this code/ }

  Read the article

• Linq, Left Join and Dates...

  - by BitFiddler

  So my situation is that I have a linq-to-sql model that does not allow dates to be null in one of my tables. This is intended, because the database does not allow nulls in that field. My problem, is that when I try to write a Linq query with this model, I cannot do a left join with that table anymore because the date is not a 'nullable' field and so I can't compare it to "Nothing". Example: There is a Movie table, {ID,MovieTitle}, and a Showings table, {ID,MovieID,ShowingTime,Location} Now I am trying to write a statement that will return all those movies that have no showings. In T.SQL this would look like: Select m.* From Movies m Left Join Showings s On m.ID = s.MovieID Where s.ShowingTime is Null Now in this situation I could test for Null on the 'Location' field but this is not what I have in reality (just a simplified example). All I have are non-null dates. I am trying to write in Linq: From m In dbContext.Movies _ Group Join s In Showings on m.ID Equals s.MovieID into MovieShowings = Group _ From ms In MovieShowings.DefaultIfEmpty _ Where ms.ShowingTime is Nothing _ Select ms However I am getting an error saying 'Is' operator does not accept operands of type 'Date'. Operands must be reference or nullable types. Is there any way around this? The model is correct, there should never be a null in the Showings:ShowTime table. But if you do a left join, and there are no show times for a particular movie, then ShowTime SHOULD be Nothing for that movie... Thanks everyone for your help.

  Read the article

• MySQL use certain columns, based on other columns

  - by Rabbott

  I have this query: SELECT COUNT(articles.id) AS count FROM articles, xml_documents, streams WHERE articles.xml_document_id = xml_documents.id AND xml_documents.stream_id = streams.id AND articles.published_at BETWEEN '2010-01-01' AND '2010-04-01' AND streams.brand_id = 7 Which just uses the default equajoin by specifying three tables in csv format in the FROM clause.. What I need to do is group this by a value found within articles.source (raw xml).. so it could turn into this: SELECT COUNT(articles.id) AS count, ExtractValue(articles.source, "/article/media_type") AS media_type FROM articles, xml_documents, streams WHERE articles.xml_document_id = xml_documents.id AND xml_documents.stream_id = streams.id AND articles.published_at BETWEEN '2010-01-01' AND '2010-04-01' AND streams.brand_id = 7 GROUP BY media_type which works fine, the problem is, I'm using rails, and using STI for the xml_documents table. The articles.source that is provided to the ExtractValue method will be of a couple different formats.. So what I need to be able to do is use "/article/media_type" IF xml_documents.type = 'source one' and use "/article/source" if xml_documents.type = 'source two' This is just because the two document types format their XML differently, but I don't want to have to run multiple queries to retrieve this information.. It would be nice if one could use a ternary operator, but i don't think this is possible.. EDIT At this Point I am looking at making a temp table, or simply using UNION to place multiple result sets together..

  Read the article

• kendo ui filtering the grid table, need some idea

  - by cool_spirit

  I want to filter the table by last name, but cant work, here is my code in controller public JsonResult Filtering() { HealthContext rc = new HealthContext(); var last = rc.Profiles.Select(lastt => new SelectListItem { Text = lastt.LastName, Value = lastt.Id.ToString() }).ToList(); return Json(last.ToList(), JsonRequestBehavior.AllowGet); } in view <script type="text/x-kendo-template" id="template"> <div class="toolbar"> <label class="category-label" for="Last name"> by last name:</label> <input type="search" id="LastName" style="width: 230px"></input> </div> </script> and also <script> $(document).ready(function() { $("#grid").kendoGrid({ dataSource: { transport: { read: { url: "/Profiles/GetJsonData", dataType: "json" } }, pageSize: 10, }, toolbar: kendo.template($("#template").html()), height: 250, filterable: true, sortable: true, pageable: true, defaultSorting: 'LastName ASC', columns: [{ field: "Id", filterable: false }, { field: "FirstName", title: "First Name", width: 100, }, { field: "LastName", title: "Last Name", width: 200 }, { field: "Gender", title: "Gender" } ] }); var dropDown = grid.find("#LastName").kendoDropDownList({ dataTextField: "LastName", dataValueField: "Id", autoBind: false, optionLabel: "All", dataSource: { severFiltering: true, transport: { read: { url: "/Profiles/Filtering", dataType: "json" } }, }, change: function() { var value = this.value(); if (value) { grid.data("kendoGrid").dataSource.filter({ field: "Id", operator: "eq", value: parseInt(value) }); } else { grid.data("kendoGrid").dataSource.filter({}); } } }); }); </script> so the problem is the drop down list is not show up as well as the value/ data, any idea guys?

  Read the article

• Big problem with Dijkstra algorithm in a linked list graph implementation

  - by Nazgulled

  Hi, I have my graph implemented with linked lists, for both vertices and edges and that is becoming an issue for the Dijkstra algorithm. As I said on a previous question, I'm converting this code that uses an adjacency matrix to work with my graph implementation. The problem is that when I find the minimum value I get an array index. This index would have match the vertex index if the graph vertexes were stored in an array instead. And the access to the vertex would be constant. I don't have time to change my graph implementation, but I do have an hash table, indexed by a unique number (but one that does not start at 0, it's like 100090000) which is the problem I'm having. Whenever I need, I use the modulo operator to get a number between 0 and the total number of vertices. This works fine for when I need an array index from the number, but when I need the number from the array index (to access the calculated minimum distance vertex in constant time), not so much. I tried to search for how to inverse the modulo operation, like, 100090000 mod 18000 = 10000 and, 10000 invmod 18000 = 100090000 but couldn't find a way to do it. My next alternative is to build some sort of reference array where, in the example above, arr[10000] = 100090000. That would fix the problem, but would require to loop the whole graph one more time. Do I have any better/easier solution with my current graph implementation?

  Read the article

• Any way for a class to prevent outside code from declaring variables of its type?

  - by supercat

  Is it possible for a class of exposing a type for function returns, without allowing users of that class to create variables of that type? A couple usage scenarios: A Fluent interface on a large class; a statement like "foo=bar.WithX(5).WithY(9).WithZ(19);" would be inefficient if it had to create three new instances of the class, but could be much more efficient if the WithX could create one instance, and the other statements could simply use it. A class may wish to support a statement like "foo[19].x = 9;" even when foo itself isn't an array, and does not hold the data in class instances that can be exposed to the public; one way to do that is to have foo[19] return a struct which holds a reference to 'foo' and the value '19', and has a member property 'x' which could call "foo.SetXValue(19, 9);" Such a struct could have a conversion operator to convert itself to the "apparent" type of foo[19]. In both of these scenarios, storing the value returned by a method or property into a variable and then using it more than once would cause strange behavior. It would be desirable if the designer of the class exposing such methods or properties could ensure that callers wouldn't be able to use them more than once. Is there any practical way to accomplish that?

  Read the article

• Alternating table row colors in freemarker

  - by itsadok

  What's a good, simple way to have alternate row coloring with freemarker? Is this really the best way? <#assign row=0> <#list items as item> <#if (row % 2) == 0> <#assign bgcolor="green"> <#else> <#assign bgcolor="red"> </#if> <tr style='background-color: ${bgcolor}'><td>${item}</td></tr> <#assign row = row + 1> </#list> I tried doing this: <#assign row=0> <#list items as item> <tr style='background-color: ${(row % 2) == 0 ? "green" : "blue"}'><td>${item}</td></tr> <#assign row = row + 1> </#list> But apparently you can't user the ternary operator in there. Note: I guess I should have mentioned it earlier, but I can't use css classes or javascript, since this HTML is going into an email message.

  Read the article

• Possible to create an implicit cast for an anonymous type to a dictionary?

  - by Ralph

  I wrote a method like this: using AttrDict = System.Collections.Generic.Dictionary<string, object>; using IAttrDict = System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object>>; static string HtmlTag(string tagName, string content = null, IAttrDict attrs = null) { var sb = new StringBuilder("<"); sb.Append(tagName); if(attrs != null) foreach (var attr in attrs) sb.AppendFormat(" {0}=\"{1}\"", attr.Key, attr.Value.ToString().EscapeQuotes()); if (content != null) sb.AppendFormat(">{0}</{1}>", content, tagName); else sb.Append(" />"); return sb.ToString(); } Which you can call like HtmlTag("div", "hello world", new AttrDict{{"class","green"}}); Not too bad. But what if I wanted to allow users to pass an anonymous type in place of the dict? Like HtmlTag("div", "hello world", new {@class="green"}); Even better! I could write the overload easily, but the problem is I'm going to have about 50 functions like this, I don't want to overload each one of them. I was hoping I could just write an implicit cast to do the work for me... public class AttrDict : Dictionary<string, object> { public static implicit operator AttrDict(object obj) { // conversion from anonymous type to AttrDict here } } But C# simply won't allow it: user-defined conversions to or from a base class are not allowed So what can I do?

  Read the article

• using ghostscript in server mode to convert pdfs to pngs

  - by emh

  while i am able to convert a specific page of a PDF to a PNG like so: gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=png16m -dGraphicsAlphaBits=4 -sOutputFile=gymnastics-20.png -dFirstPage=20 -dLastPage=20 gymnastics.pdf i am wondering if i can somehow use ghostscript's JOBSERVER mode to process several conversions without having to incur the cost of starting up ghostscript each time. from: http://pages.cs.wisc.edu/~ghost/doc/svn/Use.htm -dJOBSERVER Define \004 (^D) to start a new encapsulated job used for compatibility with Adobe PS Interpreters that ordinarily run under a job server. The -dNOOUTERSAVE switch is ignored if -dJOBSERVER is specified since job servers always execute the input PostScript under a save level, although the exitserver operator can be used to escape from the encapsulated job and execute as if the -dNOOUTERSAVE was specified. This also requires that the input be from stdin, otherwise an error will result (Error: /invalidrestore in --restore--). Example usage is: gs ... -dJOBSERVER - < inputfile.ps -or- cat inputfile.ps | gs ... -dJOBSERVER - Note: The ^D does not result in an end-of-file action on stdin as it may on some PostScript printers that rely on TBCP (Tagged Binary Communication Protocol) to cause an out-of-band ^D to signal EOF in a stream input data. This means that direct file actions on stdin such as flushfile and closefile will affect processing of data beyond the ^D in the stream. the idea is to run ghostscript in-process. the script would receive a request for a particular page of a pdf and would use ghostscript to generate the specified image. i'd rather not start up a new ghostscript process every time.

  Read the article

• Boost.MultiIndex: How to make an effective set intersection?

  - by Arman

  Hello, assume that we have a data1 and data2. How can I intersect them with std::set_intersect()? struct pID { int ID; unsigned int IDf;// postition in the file pID(int id,const unsigned int idf):ID(id),IDf(idf){} bool operator<(const pID& p)const { return ID<p.ID;} }; struct ID{}; struct IDf{}; typedef multi_index_container< pID, indexed_by< ordered_unique< tag<IDf>, BOOST_MULTI_INDEX_MEMBER(pID,unsigned int,IDf)>, ordered_non_unique< tag<ID>,BOOST_MULTI_INDEX_MEMBER(pID,int,ID)> > > pID_set; ID_set data1, data2; Load(data1); Load(data2); pID_set::index<ID>::type& L1_ID_index=L1.data.get<ID>(); pID_set::index<ID>::type& L2_ID_index=L2.data.get<ID>(); // How do I use set_intersect? Kind regards, Arman.

  Read the article

• Relative path from an ASP.NET user control NavigateUrl

  - by Daniel Ballinger

  I have a user control that contains a GridView. The GridView has both a HyperLinkField column and a template column that contains a HyperLink control. The ASP.NET project is structured as follows, with the Default.aspx page in each case using the user control. Application Root Controls UserControl with GridView SystemAdminFolder Default.aspx Edit.aspx OrganisationAdminFolder Default.aspx Edit.aspx StandardUserFolder Default.aspx Edit.aspx Note: The folders are being used to ensure the user has the correct role. I need to be able to set the DataNavigateUrlFormatString for the HyperLinkField and the NavigateUrl for the HyperLink to resolve to the Edit.aspx page in the corresponding folder. If I set the navigate URL to "Edit.aspx" the URL in the browser appears as 'http://Application Root/Controls/Edit.aspx' regardless of the originating directory. I can't use the Web application root operator (~/) as the path needs to be relative to the current page, not the application root. How can I use the same user control in multiple folders and resolve the URL to another page in the same folder? Note: The question is strongly based off a similar question by azhar2000s on the asp.net forums that matches my problem.

  Read the article

• Trying to parse OpenCV YAML ouput with yaml-cpp

  - by Kenn Sebesta

  I've got a series of OpenCv generated YAML files and would like to parse them with yaml-cpp I'm doing okay on simple stuff, but the matrix representation is proving difficult. # Center of table tableCenter: !!opencv-matrix rows: 1 cols: 2 dt: f data: [ 240, 240] This should map into the vector 240 240 with type float. My code looks like: #include "yaml.h" #include <fstream> #include <string> struct Matrix { int x; }; void operator >> (const YAML::Node& node, Matrix& matrix) { unsigned rows; node["rows"] >> rows; } int main() { std::ifstream fin("monsters.yaml"); YAML::Parser parser(fin); YAML::Node doc; Matrix m; doc["tableCenter"] >> m; return 0; } But I get terminate called after throwing an instance of 'YAML::BadDereference' what(): yaml-cpp: error at line 0, column 0: bad dereference Abort trap I searched around for some documentation for yaml-cpp, but there doesn't seem to be any, aside from a short introductory example on parsing and emitting. Unfortunately, neither of these two help in this particular circumstance. As I understand, the !! indicate that this is a user-defined type, but I don't see with yaml-cpp how to parse that.

  Read the article

• Nested dereferencing arrows in Perl: to omit or not to omit?

  - by DVK

  In Perl, when you have a nested data structure, it is permissible to omit de-referencing arrows to 2d and more level of nesting. In other words, the following two syntaxes are identical: my $hash_ref = { 1 => [ 11, 12, 13 ], 3 => [31, 32] }; my $elem1 = $hash_ref->{1}->[1]; my $elem2 = $hash_ref->{1}[1]; # exactly the same as above Now, my question is, is there a good reason to choose one style over the other? It seems to be a popular bone of stylistic contention (Just on SO, I accidentally bumped into this and this in the space of 5 minutes). So far, none of the usual suspects says anything definitive: perldoc merely says "you are free to omit the pointer dereferencing arrow". Conway's "Perl Best Practices" says "whenever possible, dereference with arrows", but it appears to only apply to the context of dereferencing the main reference, not optional arrows on 2d level of nested data structures. "MAstering Perl for Bioinfirmatics" author James Tisdall doesn't give very solid preference either: "The sharp-witted reader may have noticed that we seem to be omitting arrow operators between array subscripts. (After all, these are anonymous arrays of anonymous arrays of anonymous arrays, etc., so shouldn't they be written [$array-[$i]-[$j]-[$k]?) Perl allows this; only the arrow operator between the variable name and the first array subscript is required. It make things easier on the eyes and helps avoid carpal tunnel syndrome. On the other hand, you may prefer to keep the dereferencing arrows in place, to make it clear you are dealing with references. Your choice." Personally, i'm on the side of "always put arrows in, since itg's more readable and obvious tiy're dealing with a reference".

  Read the article

• Linking errors when building against Boost Unit Test Framework

  - by Rafid

  I am trying to use Boost Unit Test Framework by building a stand alone library as detailed here: http://www.boost.org/doc/libs/1_35_0/libs/test/doc/components/utf/compilation.html So I created a VC library project containing the mentioned files and build it and it was successful. Then I created a test project and referenced the library project I just created, but when I tried to build it, I got the following linking errors: 1>Type.obj : error LNK2019: unresolved external symbol "bool __cdecl boost::test_tools::tt_detail::check_impl(class boost::test_tools::predicate_result const &,class boost::unit_test::lazy_ostream const &,class boost::unit_test::basic_cstring<char const >,unsigned __int64,enum boost::test_tools::tt_detail::tool_level,enum boost::test_tools::tt_detail::check_type,unsigned __int64,...)" (?check_impl@tt_detail@test_tools@boost@@YA_NAEBVpredicate_result@23@AEBVlazy_ostream@unit_test@3@V?$basic_cstring@$$CBD@63@_KW4tool_level@123@W4check_type@123@3ZZ) referenced in function "public: void __cdecl test1::test_method(void)" (?test_method@test1@@QEAAXXZ) 1>BoostUnitTestFramework.lib(framework.obj) : error LNK2019: unresolved external symbol "void __cdecl boost::debug::break_memory_alloc(long)" (?break_memory_alloc@debug@boost@@YAXJ@Z) referenced in function "void __cdecl boost::unit_test::framework::init(class boost::unit_test::test_suite * (__cdecl*)(int,char * * const),int,char * * const)" (?init@framework@unit_test@boost@@YAXP6APEAVtest_suite@23@HQEAPEAD@ZH0@Z) 1>BoostUnitTestFramework.lib(framework.obj) : error LNK2019: unresolved external symbol "void __cdecl boost::debug::detect_memory_leaks(bool)" (?detect_memory_leaks@debug@boost@@YAX_N@Z) referenced in function "void __cdecl boost::unit_test::framework::init(class boost::unit_test::test_suite * (__cdecl*)(int,char * * const),int,char * * const)" (?init@framework@unit_test@boost@@YAXP6APEAVtest_suite@23@HQEAPEAD@ZH0@Z) 1>BoostUnitTestFramework.lib(execution_monitor.obj) : error LNK2019: unresolved external symbol "bool __cdecl boost::debug::attach_debugger(bool)" (?attach_debugger@debug@boost@@YA_N_N@Z) referenced in function "public: int __cdecl boost::detail::system_signal_exception::operator()(unsigned int,struct _EXCEPTION_POINTERS *)" (??Rsystem_signal_exception@detail@boost@@QEAAHIPEAU_EXCEPTION_POINTERS@@@Z) 1>BoostUnitTestFramework.lib(execution_monitor.obj) : error LNK2019: unresolved external symbol "bool __cdecl boost::debug::under_debugger(void)" (?under_debugger@debug@boost@@YA_NXZ) referenced in function "public: int __cdecl boost::execution_monitor::execute(class boost::unit_test::callback0<int> const &)" (?execute@execution_monitor@boost@@QEAAHAEBV?$callback0@H@unit_test@2@@Z) 1>BoostUnitTestFramework.lib(unit_test_main.obj) : error LNK2019: unresolved external symbol "class boost::unit_test::test_suite * __cdecl init_unit_test_suite(int,char * * const)" (?init_unit_test_suite@@YAPEAVtest_suite@unit_test@boost@@HQEAPEAD@Z) referenced in function main 1>C:\Users\Rafid\Workspace\MyPhysics\Builds\VC10\Tests\Debug\Tests.exe : fatal error LNK1120: 6 unresolved externals They seem to be mainly caused by Boost debug library, but I can't see a reason why I should get linking errors putting in mind that Boost debug library only need to be included as header files, rather than linking against as a library! Any ideas?!

  Read the article

• extracting SWF gives compiler errors in adobe flash CS4

  - by Andy

  Hey, I have been given an SWF to edit a link in the AS code. The fact is the SWF uses some XML that is generated (actually retrieved) by PHP code from a database. menuXML.load("/sub/page/dynamic.php?genre=" + genre); so the point is we can use the same SWF 'mainfraim' and fill them with different animations/sources based on the link provided in dynamic.php?genre=### Now, I've used Flash Decompiler Gold to extract all files in the SWF and can open it again in Adobe Flash to edit it. When done I enter CTRL+ENTER and there are immediately 4 compiler errors!! Errors: 1x < Unexpected 'if' encountered 2x < Statement block must be terminated by '}' 1x < Ecpected a field name after '.' operator. How can these errors be present, when the original SWF works perfectly??! If I don't manage to solve this, I'll have to find out how to create an .php file the SWF tries to use which can select the proper resources (from a database I guess) to show them (using ?genre=###) Thanks!

  Read the article

• Why can a struct defined inside a function not be used as functor to std::for_each?

  - by Oswald

  The following code won't compile. The compiler complains about *no matching function for call to for_each*. Why is this so? #include <map> #include <algorithm> struct Element { void flip() {} }; void flip_all(std::map<Element*, Element*> input) { struct FlipFunctor { void operator() (std::pair<Element* const, Element*>& item) { item.second->flip(); } }; std::for_each(input.begin(), input.end(), FlipFunctor()); } When I move struct FlipFunctor before function flip_all, the code compiles. Full error message: no matching function for call to ‘for_each(std::_Rb_tree_iterator<std::pair<Element* const, Element*> >, std::_Rb_tree_iterator<std::pair<Element* const, Element*> >, flip_all(std::map<Element*, Element*, std::less<Element*>, std::allocator<std::pair<Element* const, Element*> > >)::FlipFunctor)’

  Read the article

• Extracting images from a PDF

  - by sagar

  My Query I want to extract only images from a PDF document, using Objective-C in an iPhone Application. My Efforts I have gone through the info on this link, which has details regarding different operators on PDF documents. I also studied this document from Apple about PDF parsing with Quartz. I also went through the entire PDF reference document from the Adobe site. According to that document, for each image there are the following operators: q Q BI EI I have created a table to get the image: myTable = CGPDFOperatorTableCreate(); CGPDFOperatorTableSetCallback(myTable, "q", arrayCallback2); CGPDFOperatorTableSetCallback(myTable, "TJ", arrayCallback); CGPDFOperatorTableSetCallback(myTable, "Tj", stringCallback); I use this method to get the image: void arrayCallback2(CGPDFScannerRef inScanner, void *userInfo) { // THIS DOESN'T WORK // CGPDFStreamRef stream; // represents a sequence of bytes // if (CGPDFDictionaryGetStream (d, "BI", &stream)){ // CGPDFDataFormat t=CGPDFDataFormatJPEG2000; // CFDataRef data = CGPDFStreamCopyData (stream, &t); // } } This method is called for the operator "q", but I don't know how to extract an image from it. What should be the solution for extracting the images from the PDF documents? Thanks in advance for your kind help.

  Read the article

• Extracting bool from istream in a templated function

  - by Thomas Matthews

  I'm converting my fields class read functions into one template function. I have field classes for int, unsigned int, long, and unsigned long. These all use the same method for extracting a value from an istringstream (only the types change): template <typename Value_Type> Value_Type Extract_Value(const std::string& input_string) { std::istringstream m_string_stream; m_string_stream.str(input_string); m_string_stream.clear(); m_string_stream >> value; return; } The tricky part is with the bool (Boolean) type. There are many textual representations for Boolean: 0, 1, T, F, TRUE, FALSE, and all the case insensitive combinations Here's the questions: What does the C++ standard say are valid data to extract a bool, using the stream extraction operator? Since Boolean can be represented by text, does this involve locales? Is this platform dependent? I would like to simplify my code by not writing my own handler for bool input. I am using MS Visual Studio 2008 (version 9), C++, and Windows XP and Vista.

  Read the article

• C++ design question on traversing binary trees

  - by user231536

  I have a binary tree T which I would like to copy to another tree. Suppose I have a visit method that gets evaluated at every node: struct visit { virtual void operator() (node* n)=0; }; and I have a visitor algorithm void visitor(node* t, visit& v) { //do a preorder traversal using stack or recursion if (!t) return; v(t); visitor(t->left, v); visitor(t->right, v); } I have 2 questions: I settled on using the functor based approach because I see that boost graph does this (vertex visitors). Also I tend to repeat the same code to traverse the tree and do different things at each node. Is this a good design to get rid of duplicated code? What other alternative designs are there? How do I use this to create a new binary tree from an existing one? I can keep a stack on the visit functor if I want, but it gets tied to the algorithm in visitor. How would I incorporate postorder traversals here ? Another functor class?

  Read the article

< Previous Page | 89 90 91 92 93 94 95 96 97 98 99 100  | Next Page >