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  • What characters are NOT escaped with a mysqli prepared statement?

    - by barfoon
    Hey everyone, I'm trying to harden some of my PHP code and use mysqli prepared statements to better validate user input and prevent injection attacks. I switched away from mysqli_real_escape_string as it does not escape % and _. However, when I create my query as a mysqli prepared statement, the same flaw is still present. The query pulls a users salt value based on their username. I'd do something similar for passwords and other lookups. Code: $db = new sitedatalayer(); if ($stmt = $db->_conn->prepare("SELECT `salt` FROM admins WHERE `username` LIKE ? LIMIT 1")) { $stmt->bind_param('s', $username); $stmt->execute(); $stmt->bind_result($salt); while ($stmt->fetch()) { printf("%s\n", $salt); } $stmt->close(); } else return false; Am I composing the statement correctly? If I am what other characters need to be examined? What other flaws are there? What is best practice for doing these types of selects? Thanks,

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  • How do I implement a collection in Scala 2.8?

    - by Simon Reinhardt
    In trying to write an API I'm struggling with Scala's collections in 2.8(.0-beta1). Basically what I need is to write something that: adds functionality to immutable sets of a certain type where all methods like filter and map return a collection of the same type without having to override everything (which is why I went for 2.8 in the first place) where all collections you gain through those methods are constructed with the same parameters the original collection had (similar to how SortedSet hands through an ordering via implicits) which is still a trait in itself, independent of any set implementations. Additionally I want to define a default implementation, for example based on a HashSet. The companion object of the trait might use this default implementation. I'm not sure yet if I need the full power of builder factories to map my collection type to other collection types. I read the paper on the redesign of the collections API but it seems like things have changed a bit since then and I'm missing some details in there. I've also digged through the collections source code but I'm not sure it's very consistent yet. Ideally what I'd like to see is either a hands-on tutorial that tells me step-by-step just the bits that I need or an extensive description of all the details so I can judge myself which bits I need. I liked the chapter on object equality in "Programming in Scala". :-) But I appreciate any pointers to documentation or examples that help me understand the new collections design better.

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  • MMGR Questions, code use and thread-saftey

    - by chadb
    1) Is MMGR thread safe? 2) I was hoping someone could help me understand some code. I am looking at something where a macro is used, but I don't understand the macro. I know it contains a function call and an if check, however, the function is a void function. How does wrapping "(m_setOwner (FILE,_LINE_,FUNCTION),false)" ever change return types? #define someMacro (m_setOwner(__FILE__,__LINE__,__FUNCTION__),false) ? NULL : new ... void m_setOwner(const char *file, const unsigned int line, const char *func); 3) What is the point of the reservoir? 4) On line 770 ("void *operator new(size_t reportedSize)" there is the line "// ANSI says: allocation requests of 0 bytes will still return a valid value" Who/what is ANSI in this context? Do they mean the standards? 5) This is more of C++ standards, but where does "reportedSize" come from for "void *operator new(size_t reportedSize)"? 6) Is this the code that is actually doing the allocation needed? "au-actualAddress = malloc(au-actualSize);"

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  • pulling a value from NSMutableDictionary

    - by Jared Gross
    I have a dictionary array with a key:@"titleLabel". I am trying to load a pickerView with ONE instance of each @"titleLabel" key so that if there are multiple objects with the same @"titleLabel" only one title will be displayed. I've done some research on this forum and looked at apples docs but haven't been able to put the puzzle together. Below is my code but I am having trouble pulling the values. Right now when I run this code it throws an error Incompatible pointer types sending 'PFObject *' to parameter of type 'NSString' which i understand but am just not sure how to remedy. Cheers! else { // found messages! self.objectsArray = objects; NSMutableDictionary *dict = [[NSMutableDictionary alloc] init]; for(id obj in self.objectsArray){ PFObject *key = [self.objectsArray valueForKey:@"titleLabel"]; if(![dict objectForKey:@"titleLabel"]){ [dict setValue:obj forKey:key]; } } for (id key in dict) { NSLog(@"Objects array is %d", [self.objectsArray count]); NSLog(@"key: %@, value: %@ \n", key, [dict objectForKey:key]); } [self.pickerView reloadComponent:0]; } }];` Here is where I define the PFObject and keys: PFObject *image = [PFObject objectWithClassName:@"Images"]; [image setObject:file forKey:@"file"]; [image setObject:fileType forKey:@"fileType"]; [image setObject:title forKey:@"titleLabel"]; [image setObject:self.recipients forKey:@"recipientIds"]; [image setObject:[[PFUser currentUser] objectId] forKey:@"senderId"]; [image setObject:[[PFUser currentUser] username] forKey:@"senderName"]; [image saveInBackground];

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  • Survey statistic diagram ideas

    - by Nort
    Hey everyone, I've got some homework tasks in topic surveys and diagrams. The first task is to normalize the input of a survey, because the structure of the data is changing from time-to-time. So there are three types of surveys: static fields, where text is stored dynamic ones, where the user can select one option and multiselect fields, where the user can select multiple options So I'm not really a statistics guy, so I have really no idea what I can do with that incomming data. So the data I have is stored in an orbital XML file from there I can easily get how man times a survey was filled, and how many times a field was filled, so I can (for eg on a pie chart show the relation of filled or not filled). The second idea is to show the relation between the content of a multi option element using a bar chart or so. In case of the multi option elements I've got the idea to show data in implication of one option. But the question is, what could be shown? The other problem are the static elements (text fields and so). What data could be represented from a single field? The data in the XML field is collected from 2001 to 2005 So maybe I can work with the dates of the surveys, but as I said, i don't really know how to process the data, to collect as much data as possible.

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  • PHP Outputting File Attachments with Headers

    - by OneNerd
    After reading a few posts here I formulated this function which is sort of a mishmash of a bunch of others: function outputFile( $filePath, $fileName, $mimeType = '' ) { // Setup $mimeTypes = array( 'pdf' => 'application/pdf', 'txt' => 'text/plain', 'html' => 'text/html', 'exe' => 'application/octet-stream', 'zip' => 'application/zip', 'doc' => 'application/msword', 'xls' => 'application/vnd.ms-excel', 'ppt' => 'application/vnd.ms-powerpoint', 'gif' => 'image/gif', 'png' => 'image/png', 'jpeg' => 'image/jpg', 'jpg' => 'image/jpg', 'php' => 'text/plain' ); // Send Headers //-- next line fixed as per suggestion -- header('Content-Type: ' . $mimeTypes[$mimeType]); header('Content-Disposition: attachment; filename="' . $fileName . '"'); header('Content-Transfer-Encoding: binary'); header('Accept-Ranges: bytes'); header('Cache-Control: private'); header('Pragma: private'); header('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); readfile($filePath); } I have a php page (file.php) which does something like this (lots of other code stripped out): // I run this thru a safe function not shown here $safe_filename = $_GET['filename']; outputFile ( "/the/file/path/{$safe_filename}", $safe_filename, substr($safe_filename, -3) ); Seems like it should work, and it almost does, but I am having the following issues: When its a text file, I am getting a strange symbol as the first letter in the text document When its a word doc, it is corrupt (presumably that same first bit or byte throwing things off). I presume all other file types will be corrupt - have not even tried them Any ideas on what I am doing wrong? Thanks - UPDATE: changed line of code as suggested - still same issue.

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  • IPad SQLite Push and Pull Data from external MS SQL Server DB

    - by MattyD
    This carries on from my previous post (http://stackoverflow.com/questions/4182664/ipad-app-pull-and-push-relational-data). My plan is that when the ipad application starts I am going to pull data (config data i.e. Departments, Types etc etc relational data that is used across the system) from a webhosted MS SQL Server DB via a webservice and populate it into an SQL Lite DB on the IPad. Then when I load a listing I will pull the data over the line again via a webservice and populate it into the SQL Lite db on the ipad (than just run select commands to populate the listing). My questions are: 1. What is the most efficient way to transfer data across the line via the web? Everyone seems to do it a different way. My idea is that I will have a webService for each type of data pull (e.g. RetrieveContactListing) that will query the db and than convert that data into "something" to send across the line. My question really is what is the "something" that it should be converting into? 2. Everyone talks about odata services. Is this suited for applications where complex read and writes are needed? Ive created a simple iphone app before that talked to an sql server db (i just sent my own structured xml across the line) but now with this app the data calls are going to be a lot larger so efficiency is key.

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  • Analyzing an IronPython Scope

    - by Vercinegetorix
    I'm trying to write C# code with an embedded IronPython script. Then want to analyze the contents of the script, i.e. list all variables, functions, class and their members/methods. There's an easy way to start, assuming I've got a scope defined and code executed in it already: dynamic variables=pyScope.GetVariables(); foreach (string v in variables) { dynamic dynamicV=pyScope.GetVariable(); /*seems to return everything. variables, functions, classes, instances of classes*/ } But how do I figure out what the type of a variable is? For the following python 'objects', dynamicV.GetType() will return different values: x=5 --system.Int32 y="asdf" --system.String def func():... --IronPython.Runtime.PythonFunction z=class() -- IronPython.Runtime.Types.OldInstance, how can I identify what the actual python class is? class NewClass -- throws an error, GetType() is unavailable. This is almost what I'm looking for. I could capture the exception thrown when unavailable and assume it's a class declaration, but that seems unclean. Is there a better approach? To discover the members/methods of a class it looks like I can use: ObjectOperations op = pyEngine.Operations; object instance = op.Call("className"); foreach (string j in op.GetMemberNames("className")) { object member=op.GetMember(instance, j); Console.WriteLine(member.GetType()); /*once again, GetType() provides some info about the type of the member, but returns null sometimes*/ } Also, how do I get the parameters to a method? Thanks!

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  • Optimizing T-SQL where an array would be nice

    - by Polatrite
    Alright, first you'll need to grab a barf bag. I've been tasked with optimizing several old stored procedures in our database. This SP does the following: 1) cursor loops through a series of "buildings" 2) cursor loops through a week, Sunday-Saturday 3) has a huge set of IF blocks that are responsible for counting how many Objects of what Types are present in a given building Essentially what you'll see in this code block is that, if there are 5 objects of type #2, it will increment @Type_2_Objects_5 by 1. IF @Number_Type_1_Objects = 0 BEGIN SET @Type_1_Objects_0 = @Type_1_Objects_0 + 1 END IF @Number_Type_1_Objects = 1 BEGIN SET @Type_1_Objects_1 = @Type_1_Objects_1 + 1 END IF @Number_Type_1_Objects = 2 BEGIN SET @Type_1_Objects_2 = @Type_1_Objects_2 + 1 END IF @Number_Type_1_Objects = 3 BEGIN SET @Type_1_Objects_3 = @Type_1_Objects_3 + 1 END [... Objects_4 through Objects_20 for Type_1] IF @Number_Type_2_Objects = 0 BEGIN SET @Type_2_Objects_0 = @Type_2_Objects_0 + 1 END IF @Number_Type_2_Objects = 1 BEGIN SET @Type_2_Objects_1 = @Type_2_Objects_1 + 1 END IF @Number_Type_2_Objects = 2 BEGIN SET @Type_2_Objects_2 = @Type_2_Objects_2 + 1 END IF @Number_Type_2_Objects = 3 BEGIN SET @Type_2_Objects_3 = @Type_2_Objects_3 + 1 END [... Objects_4 through Objects_20 for Type_2] In addition to being extremely hacky (and limited to a quantity of 20 objects), it seems like a terrible way of handling this. In a traditional language, this could easily be solved with a 2-dimensional array... objects[type][quantity] += 1; I'm a T-SQL novice, but since writing stored procedures often uses a lot of temporary tables (which could essentially be a 2-dimensional array) I was wondering if someone could illuminate a better way of handling a situation like this with two dynamic pieces of data to store. Requested in comments: The columns are simply Number_Type_1_Objects, Number_Type_2_Objects, Number_Type_3_Objects, Number_Type_4_Objects, Number_Type_5_Objects, and CurrentDateTime. Each row in the table represents 5 minutes. The expected output is to figure out what percentage of time a given quantity of objects is present throughout each day. Sunday - Object Type 1 0 objects - 69 rows, 5:45, 34.85% 1 object - 85 rows, 7:05, 42.93% 2 objects - 44 rows, 3:40, 22.22% On Sunday, there were 0 objects of type 1 for 34.85% of the day. There was 1 object for 42.93% of the day, and 2 objects for 22.22% of the day. Repeat for each object type.

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  • C# Multiple constraints

    - by John
    I have an application with lots of generics and IoC. I have an interface like this: public interface IRepository<TType, TKeyType> : IRepo Then I have a bunch of tests for my different implementations of IRepository. Many of the objects have dependencies on other objects so for the purpose of testing I want to just grab one that is valid. I can define a separate method for each of them: public static EmailType GetEmailType() { return ContainerManager.Container.Resolve<IEmailTypeRepository>().GetList().FirstOrDefault(); } But I want to make this generic so it can by used to get any object from the repository it works with. I defined this: public static R GetItem<T, R>() where T : IRepository<R, int> { return ContainerManager.Container.Resolve<T>().GetList().FirstOrDefault(); } This works fine for the implementations that use an integer for the key. But I also have repositories that use string. So, I do this now: public static R GetItem<T, R, W>() where T : IRepository<R, W> This works fine. But I'd like to restrict 'W' to either int or string. Is there a way to do that? The shortest question is, can I constrain a generic parameter to one of multiple types?

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  • Automatically restarting Erlang applications

    - by Nick
    I recently ran into a bug where an entire Erlang application died, yielding a log message that looked like this: =INFO REPORT==== 11-Jun-2010::11:07:25 === application: myapp exited: shutdown type: temporary I have no idea what triggered this shutdown, but the real problem I have is that it didn't restart itself. Instead, the now-empty Erlang VM just sat there doing nothing. Now, from the research I've done, it looks like there are other "start types" you can give an application: 'transient' and 'permanent'. If I start a Supervisor within an application, I can tell it to make a particular process transient or permanent, and it will automatically restart it for me. However, according to the documentation, if I make an application transient or permanent, it doesn't restart it when it dies, but rather it kills all the other applications as well. What I really want to do is somehow tell the Erlang VM that a particular application should always be running, and if it goes down, restart it. Is this possible to do? (I'm not talking about implementing a supervisor on top of my application, because then it's a catch 22: what if my supervisor process crashes? I'm looking for some sort of API or setting that I can use to have Erlang monitor and restart my application for me.) Thanks!

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  • is there a better way to write this frankenstein LINQ query that searches for values in a child tabl

    - by MRV
    I have a table of Users and a one to many UserSkills table. I need to be able to search for users based on skills. This query takes a list of desired skills and searches for users who have those skills. I want to sort the users based on the number of desired skills they posses. So if a users only has 1 of 3 desired skills he will be further down the list than the user who has 3 of 3 desired skills. I start with my comma separated list of skill IDs that are being searched for: List<short> searchedSkillsRaw = skills.Value.Split(',').Select(i => short.Parse(i)).ToList(); I then filter out only the types of users that are searchable: List<User> users = (from u in db.Users where u.Verified == true && u.Level > 0 && u.Type == 1 && (u.UserDetail.City == city.SelectedValue || u.UserDetail.City == null) select u).ToList(); and then comes the crazy part: var fUsers = from u in users select new { u.Id, u.FirstName, u.LastName, u.UserName, UserPhone = u.UserDetail.Phone, UserSkills = (from uskills in u.UserSkills join skillsJoin in configSkills on uskills.SkillId equals skillsJoin.ValueIdInt into tempSkills from skillsJoin in tempSkills.DefaultIfEmpty() where uskills.UserId == u.Id select new { SkillId = uskills.SkillId, SkillName = skillsJoin.Name, SkillNameFound = searchedSkillsRaw.Contains(uskills.SkillId) }), UserSkillsFound = (from uskills in u.UserSkills where uskills.UserId == u.Id && searchedSkillsRaw.Contains(uskills.SkillId) select uskills.UserId).Count() } into userResults where userResults.UserSkillsFound > 0 orderby userResults.UserSkillsFound descending select userResults; and this works! But it seems super bloated and inefficient to me. Especially the secondary part that counts the number of skills found. Thanks for any advice you can give. --r

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  • Solr : how do i index and search several fields?

    - by sbrattla
    Hi, I've set up my first 'installation' of Solr, where each index (document) represents a musical work (with properties like number (int), title (string), version (string), composers (string) and keywords (string)). I've set the field 'title' as the default search field. However, what do I do when I would like to do a query on all fields? I'd like to give users the opportunity to search in all fields, and as far as I've understood there is at least two options for this: (1) Specify which fields the query should be made against. (2) Set up the Solr configuration with copyfields, so that values added to each of the fields will be copied to a 'catch-all'-like field which can be used for searching. However, in this case, i am uncertain how things would turn out when i take into consideration that the data types are not all the same for the various fields (the various fields will to a lesser og greater degree go through filters, but as copyfield values are taken from their original fields before the values have been run through their original fields' filters, i would have to apply one single filter to all values on the copyfield. This, again, would result in integers being 'filtered' just as strings would). Is this a case where i should use copyfields? At first glance, it seems a bit more 'flexible' to rather just search on all fields. However, maybe there's a cost? All feedback appreciated! Thanks!

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  • Delphi: How to avoid EIntOverflow underflow when subtracting?

    - by Ian Boyd
    Microsoft already says, in the documentation for GetTickCount, that you could never compare tick counts to check if an interval has passed. e.g.: Incorrect (pseudo-code): DWORD endTime = GetTickCount + 10000; //10 s from now ... if (GetTickCount > endTime) break; The above code is bad because it is suceptable to rollover of the tick counter. For example, assume that the clock is near the end of it's range: endTime = 0xfffffe00 + 10000 = 0x00002510; //9,488 decimal Then you perform your check: if (GetTickCount > endTime) Which is satisfied immediatly, since GetTickCount is larger than endTime: if (0xfffffe01 > 0x00002510) The solution Instead you should always subtract the two time intervals: DWORD startTime = GetTickCount; ... if (GetTickCount - startTime) > 10000 //if it's been 10 seconds break; Looking at the same math: if (GetTickCount - startTime) > 10000 if (0xfffffe01 - 0xfffffe00) > 10000 if (1 > 10000) Which is all well and good in C/C++, where the compiler behaves a certain way. But what about Delphi? But when i perform the same math in Delphi, with overflow checking on ({Q+}, {$OVERFLOWCHECKS ON}), the subtraction of the two tick counts generates an EIntOverflow exception when the TickCount rolls over: if (0x00000100 - 0xffffff00) > 10000 0x00000100 - 0xffffff00 = 0x00000200 What is the intended solution for this problem? Edit: i've tried to temporarily turn off OVERFLOWCHECKS: {$OVERFLOWCHECKS OFF}] delta = GetTickCount - startTime; {$OVERFLOWCHECKS ON} But the subtraction still throws an EIntOverflow exception. Is there a better solution, involving casts and larger intermediate variable types?

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  • Get XML-RPC (Andorid - PHP) web service different params type

    - by Jovan
    Hi, I want to create XML-RPC web service for Andorid (client) - PHP (Server) communication I create XML-RPC PHP web service server using this tutorial: http://articles.sitepoint.com/article/own-web-service-php-xml-rpc/5 For andorid client web service I use this project: http://code.google.com/p/android-xmlrpc/ server and client communication is OK, but I have problem with getting params from andorid client to php server. From andorid client I send two params (first integer and second float number) Object[] params = { 3, 3.6f, }; method.call(params); , but I don't know how to handle this parameters in php server?? in php server there is some function , but with only one param ($news_id): function news_viewNewsItem ( $news_id ) { /* Define the query to fetch the news item */ $query = "SELECT * FROM kd_xmlrpc_news WHERE news_id = '" . $news_id . "'"; $sql = mysql_query ( $query ); if ( $result = mysql_fetch_array ( $sql ) ) { /* Extract the variables for sending in our server response */ $news_item['news_id'] = $result['news_id']; $news_item['date'] = XMLRPC_convert_timestamp_to_iso8601( mysql_datetime_to_timestamp( $result['date'] ) ); $news_item['title'] = $result['title']; $news_item['full_desc'] = $result['full_desc']; $news_item['author'] = $result['author']; /* Respond to the client with the news item */ XMLRPC_response(XMLRPC_prepare($news_item), KD_XMLRPC_USERAGENT); } else { /* If there was an error, respond with a fault code instead */ XMLRPC_error("1", "news_viewNewsItem() error: Unable to read news:" . mysql_error(), KD_XMLRPC_USERAGENT); } } In server.py file there is functions for every method but I dont know how to write in php server: def add(self, x, y): print print "input x=%s, y=%s" % (str(x), str(y)) sum = x + y print "output", sum print return sum Can some one help me with code , and tell me how to handle various types from client to server?? Thanks and Happy New Year

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  • Could I do this blind relative to absolute path conversion (for perforce depot paths) better?

    - by wonderfulthunk
    I need to "blindly" (i.e. without access to the filesystem, in this case the source control server) convert some relative paths to absolute paths. So I'm playing with dotdots and indices. For those that are curious I have a log file produced by someone else's tool that sometimes outputs relative paths, and for performance reasons I don't want to access the source control server where the paths are located to check if they're valid and more easily convert them to their absolute path equivalents. I've gone through a number of (probably foolish) iterations trying to get it to work - mostly a few variations of iterating over the array of folders and trying delete_at(index) and delete_at(index-1) but my index kept incrementing while I was deleting elements of the array out from under myself, which didn't work for cases with multiple dotdots. Any tips on improving it in general or specifically the lack of non-consecutive dotdot support would be welcome. Currently this is working with my limited examples, but I think it could be improved. It can't handle non-consecutive '..' directories, and I am probably doing a lot of wasteful (and error-prone) things that I probably don't need to do because I'm a bit of a hack. I've found a lot of examples of converting other types of relative paths using other languages, but none of them seemed to fit my situation. These are my example paths that I need to convert, from: //depot/foo/../bar/single.c //depot/foo/docs/../../other/double.c //depot/foo/usr/bin/../../../else/more/triple.c to: //depot/bar/single.c //depot/other/double.c //depot/else/more/triple.c And my script: begin paths = File.open(ARGV[0]).readlines puts(paths) new_paths = Array.new paths.each { |path| folders = path.split('/') if ( folders.include?('..') ) num_dotdots = 0 first_dotdot = folders.index('..') last_dotdot = folders.rindex('..') folders.each { |item| if ( item == '..' ) num_dotdots += 1 end } if ( first_dotdot and ( num_dotdots > 0 ) ) # this might be redundant? folders.slice!(first_dotdot - num_dotdots..last_dotdot) # dependent on consecutive dotdots only end end folders.map! { |elem| if ( elem !~ /\n/ ) elem = elem + '/' else elem = elem end } new_paths << folders.to_s } puts(new_paths) end

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  • How do I select dynamic ids in this format?

    - by sjsc
    I'm trying to select dynamic ids when a user types something into the input fields. My app spits out the input fields in the following format: <input id="student_1_first_name" /> <input id="student_1_last_name" /> <input id="student_2_first_name" /> <input id="student_2_last_name" /> <input id="student_3_first_name" /> <input id="student_3_last_name" /> etc. For example, I tried doing this to select the end of the id string: <script type="text/javascript"> $(document).ready( function (){ $("input[id$=_first_name]").bind("keyup", run_some_function_here); run_some_function_here(); $("input[id$=_last_name]").bind("keyup", run_some_function_here); run_some_function_here(); } ); </script> When I do that, Jquery can't seem to select the input ids, so the functions don't run. Do you have any ideas on how I can select the ids correctly?

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  • Pre-formatting text to prevent reflowing

    - by mattjn
    I've written a fairly simple script that will take elements (in this case, <p> elements are the main concern) and type their contents out like a typewriter, one by one. The problem is that as it types, when it reaches the edge of the container mid-word, it reflows the text and jumps to the next line (like word wrap in any text editor). This is, of course, expected behavior; however, I would like to pre-format the text so that this does not happen. I figure that inserting <br> before the word that will wrap would be the best solution, but I'm not quite sure what the best way to go about doing that is that supports all font sizes and container widths, while also keeping any HTML tags intact. I figure something involving a hidden <span> element, adding text to it gradually and checking its width against the container width might be on the right track, but I'm not quite sure how to actually put this together. Any help or suggestions on better methods would be appreciated.

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  • Why does this Haskell code produce the "infinite type" error?

    - by Charlie Flowers
    I am new to Haskell and facing a "cannot construct infinite type" error that I cannot make sense of. In fact, beyond that, I have not been able to find a good explanation of what this error even means, so if you could go beyond my basic question and explain the "infinite type" error, I'd really appreciate it. Here's the code: intersperse :: a -> [[a]] -> [a] -- intersperse '*' ["foo","bar","baz","quux"] -- should produce the following: -- "foo*bar*baz*quux" -- intersperse -99 [ [1,2,3],[4,5,6],[7,8,9]] -- should produce the following: -- [1,2,3,-99,4,5,6,-99,7,8,9] intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:y:xs) = x:s:y:intersperse s xs And here's the error trying to load it into the interpreter: Prelude :load ./chapter.3.ending.real.world.haskell.exercises.hs [1 of 1] Compiling Main ( chapter.3.ending.real.world.haskell.exercises.hs, interpreted ) chapter.3.ending.real.world.haskell.exercises.hs:147:0: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `intersperse' Failed, modules loaded: none. Thanks. EDIT: Thanks to the responses, I have corrected the code and I also have a general guideline for dealing with the "infinite type" error in Haskell: Corrected code intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:xs) = x ++ s:intersperse s xs What the problem was: My type signature states that the second parameter to intersperse is a list of lists. Therefore, when I pattern matched against "s (x:y:xs)", x and y became lists. And yet I was treating x and y as elements, not lists. Guideline for dealing with the "infinite type" error: Most of the time, when you get this error, you have forgotten the types of the various variables you're dealing with, and you have attempted to use a variable as if it were some other type than what it is. Look carefully at what type everything is versus how you're using it, and this will usually uncover the problem.

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  • How to hide helper functions from public API in c

    - by emge
    I'm working on a project and I need to create an API. I am using sockets to communicate between the server (my application) and the clients (the other applications using my API). This project is in c not C++ I come from a linux background and this is my first project using Windows, Visual Studio 2008, and dll libraries. I have communication working between the client and server, but I have some that is duplicated on both projects. I would like to create a library (probably a dll file), that both projects can link to so I don't have to maintain extra code. I also have to create the library that has the API that I need to make available for my clients. Within the API functions that I want public are the calls to these helper functions that are "duplicated code", I don't want to expose these functions to my client, but I do want my server to be able to use those functions. How can I do this? I will try to clarify with an example. This is what I started with. Server Project: int Server_GetPacket(SOCKET sd); int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); Client Project: int Client_SendCommand(int command); int Client_GetData(int command, char *buf, int len); int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); This is kind of what I would like to end up with: //Server Project: int Server_GetPacket(SOCKET sd); // library with public and private types // private API (not exposed to my client) int ReceiveAll(SOCKET sd, char *buf, int len); int VerifyLen(char *buf); // public API (header file available for client) int Client_SendCommand(int command); int Client_GetData(int command, char *buf, int len); Thanks any help would be appreciated.

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  • Starting an STA thread, but with parameters to the final function

    - by DRapp
    I'm a bit weak on how some delegates behave, such as passing a method as the parameter to be invoked. While trying to do some NUnit test scripts, I have something that I need to run many test with. Each of these tests requires a GUI created and thus the need for an STA thread. So, I have something like public class MyTest { // the Delegate "ThreadStart" is part of the System.Threading namespace and is defined as // public delegate void ThreadStart(); protected void Start_STA_Thread(ThreadStart whichMethod) { Thread thread = new Thread(whichMethod); thread.SetApartmentState(ApartmentState.STA); //Set the thread to STA thread.Start(); thread.Join(); } [Test] public void Test101() { // Since the thread issues an INVOKE of a method, I'm having it call the // corresponding "FromSTAThread" method, such as Start_STA_Thread( Test101FromSTAThread ); } protected void Test101FromSTAThread() { MySTA_RequiredClass oTmp = new MySTA_RequiredClass(); Assert.IsTrue( oTmp.DoSomething() ); } } This part all works fine... Now the next step. I now have a different set of tests that ALSO require an STA thread. However, each "thing" I need to do requires two parameters... both strings (for this case). How do I go about declaring proper delegate so I can pass in the method I need to invoke, AND the two string parameters in one shot... I may have 20+ tests to run with in this pattern and may have future of other similar tests with different parameter counts and types of parameters too. Thanks.

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  • Open closed prinicple, problem

    - by Marcus
    Hi, I'm trying to apply OCP to a code snippet I have that in it's current state is really smelly, but I feel I'm not getting all the way to the end. Current code: public abstract class SomeObject {} public class SpecificObject1 : SomeObject {} public class SpecificObject2 : SomeObject {} // Smelly code public class Model { public void Store(SomeObject someObject) { if (someObject is SpecificObject1) {} else if (someObject is SpecificObject2) {} } } That is really ugly, my new approach looks like this: // No so smelly code public class Model { public void Store(SomeObject someObject) { throw new Expception("Not allowed!"); } public void Store(SpecificObject1 someObject) {} public void Store(SpecificObject2 someObject) {} } When a new SomeObject type comes along I must implement how that specific object is stored, this will break OCP cause I need to alter the Model-class. To move the store logic to SomeObject also feels wrong cause then I will violate SRP (?), becuase in this case the SomeObject is almost like a DTO, it's resposibility it not how to know to store itself. If a new implementation to SomeObject comes along who's store implementation is missing I will get a runtime error due to exception in Store method in Model class, it also feels like a code smell. This is because calling code will in the form of IEnumerable<SomeObject> sequence; I will not know the specific types of the sequence objects. I can't seem to grasp the OCP-concept. Anyone has any concrete examples or links that is a bit more than just some Car/Fruit example?

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  • "Most popular" GROUP BY in LINQ?

    - by tags2k
    Assuming a table of tags like the stackoverflow question tags: TagID (bigint), QuestionID (bigint), Tag (varchar) What is the most efficient way to get the 25 most used tags using LINQ? In SQL, a simple GROUP BY will do: SELECT Tag, COUNT(Tag) FROM Tags GROUP BY Tag I've written some LINQ that works: var groups = from t in DataContext.Tags group t by t.Tag into g select new { Tag = g.Key, Frequency = g.Count() }; return groups.OrderByDescending(g => g.Frequency).Take(25); Like, really? Isn't this mega-verbose? The sad thing is that I'm doing this to save a massive number of queries, as my Tag objects already contain a Frequency property that would otherwise need to check back with the database for every Tag if I actually used the property. So I then parse these anonymous types back into Tag objects: groups.OrderByDescending(g => g.Frequency).Take(25).ToList().ForEach(t => tags.Add(new Tag() { Tag = t.Tag, Frequency = t.Frequency })); I'm a LINQ newbie, and this doesn't seem right. Please show me how it's really done.

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  • JPA entitylisteners and @embeddable

    - by seanizer
    I have a class hierarchy of JPA entities that all inherit from a BaseEntity class: @MappedSuperclass @EntityListeners( { ValidatorListener.class }) public abstract class BaseEntity implements Serializable { // other stuff } I want all entities that implement a given interface to be validated automatically on persist and/or update. Here's what I've got. My ValidatorListener: public class ValidatorListener { private enum Type { PERSIST, UPDATE } @PrePersist public void checkPersist(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.PERSIST); } } @PreUpdate public void checkUpdate(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.UPDATE); } } private void check(final Validateable entity, final Type persist) { switch (persist) { case PERSIST: if (entity instanceof Persist) { ((Persist) entity).persist(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; case UPDATE: if (entity instanceof Update) { ((Update) entity).update(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; default: break; } } } and here's my Validateable interface that it checks against (the outer interface is just a marker, the inner contain the methods): public interface Validateable { interface Persist extends Validateable { void persist(); } interface PersistOrUpdate extends Validateable { void persistOrUpdate(); } interface Update extends Validateable { void update(); } } All of this works, however I would like to extend this behavior to Embeddable classes. I know two solutions: call the validation method of the embeddable object manually from the entity validation method: public void persistOrUpdate(){ // validate my own properties first // then manually validate the embeddable property: myEmbeddable.persistOrUpdate(); // this works but I'd like something that I don't have to call manually } use reflection, checking all properties to see if their type is of one of their interface types. This would work, but it's not pretty. Is there a more elegant solution?

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  • Selectind DOM elements based on attribute content

    - by sameold
    I have several types of <a> in my document. I'd like to select only the <a> whose title attribute begins with the text "more data ..." like <a title="more data *"> For example given the markup below, I'd like to select the first and second <a>, but skip the third because title doesn't begin with more data, and skip the 4th because <a> doesn't even have a title attribute. <a title="more data some text" href="http://mypage.com/page.html">More</a> <a title="more data other text" href="http://mypage.com/page.html">More</a> <a title="not needed" href="http://mypage.com/page.html">Not needed</a> <a href="http://mypage.com/page.html">Not needed</a> I'm using DOMXPath. How would my query look like? $xpath = new DOMXPath($doc); $q = $xpath->query('//a');

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