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• Is pthread_spin_trylock safe inside of sigsegv handler of multithreaded application?

  - by TWMouton

  I am trying to implement a handler that on SIGSEGV will collect some information such as process-id, thread-id and a backtrace and write this information to a file/pipe/socket. The problem lies in that there is the (probably pretty high) possibility that if one thread experienced a SIGSEGV that the others will shortly follow. If two threads happen to make it to the bit of code where they're writing their report out at the same time then they'll interleave their writing (to the same file). I know that I should only be using async-signal-safe functions as detailed in signal(7) I also have seen at least two cases here and video linked in top answer here where others have used pthread_spin_trylock to get around this problem. Is this a safe way to prevent the above problem?

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• maching strings

  - by kiran

  Write two functions, called countSubStringMatch and countSubStringMatchRecursive that take two arguments, a key string and a target string. These functions iteratively and recursively count the number of instances of the key in the target string. You should complete definitions for def countSubStringMatch(target,key): and def countSubStringMatchRecursive (target, key): For the remaining problems, we are going to explore other substring matching ideas. These problems can be solved with either an iterative function or a recursive one. You are welcome to use either approach, though you may find iterative approaches more intuitive in these cases of matching linear structures.

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• CASE + IF MysQL query

  - by terence6

  Problem is as follows. I have a product that can be in one of three categories (defined by category_id). Each category table has category_id field related to category_id in product table. So I have 3 cases. I'm checking If my product.category_id is in table one. If yes, I take some values. If not I check in tables that are left. What can I write In the ELSE section? Can anyone correct my query ? CASE WHEN IF EXISTS(SELECT * FROM table1 WHERE category_id='category_id') THEN SELECT type_id FROM table1 WHERE category_id='category_id'; WHEN IF EXISTS(SELECT * FROM table2 WHERE category_id='category_id') THEN SELECT value_id FROM table2 WHERE category_id='category_id'; WHEN IF EXISTS(SELECT * FROM table3 WHERE category_id='category_id') THEN SELECT group_id FROM table3 WHERE category_id='category_id'; ELSE "dont know what here"; END;

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• Using xval with fields containing periods

  - by JP

  Hello, I have been using xVal with success for a while but this evening ran into an issue where a field containing a period would not be validated (client or server-side). I am using ASP.NET MVC2 and need to use the period syntax in cases where I am model binding to a list. In the below example I am using a textbox for the sake of simplicity: xVal.AttachValidator(null, { "Fields": [{ "FieldName": "entry[622592].Value", "FieldRules": [{ "RuleName": "Required", "RuleParameters": {}}]}] }, {}) <input type="text" class="text" name="entry[622592].Value"/> If I replace both instances of "entry[622592].Value" to something trivial like "test" then the validation works successfully, but if i leave it this way the validation never appears to fire... Has anyone run into this issue? Thanks in advance!

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• Writing loops with i++ or ++i [duplicate]

  - by Nonesuch

  This question already has an answer here: Why use ++i instead of i++ in cases where the value is not used anywhere else in the statement? 6 answers format of for loops 31 answers I have a question about writing loops. I always begin with (int i=0; i<10; i++) But I see many experts begin with (int i=0; i<10; ++i) Is there there any real difference, or they are same? Of course, I know the difference between pre-increment and post-increment. I mean which one I should use when writing the loop? or it depends. Thanks!

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• [C] How I change a variable of a type to another one?

  - by drigoSkalWalker

  I want to do it: int main () { bla bla bla void *onetype; switch (USER_INPUT_TYPE) { CASE CONVERT_TO_CHAR: convert onetype VOID TO CHAR HOW??? CASE CONVERT_TO_INT: convert onetype VOID TO INT HOW??? LOT OF CASES... } } Yes, I know type casting, but type casting is a 'temporary' change... So...Is there any way to accomplish it in C? EDIT : Stop stop stop! Please, see, what are you doing is type casting, I KNOW THIS, you are creating another variable of the desirable type like int i = (int) onetype, I don't want this, I want something else like onetype = (int) onetype, without recreate them, without allocate another variable. Thanks a lot guys!

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• Delphi: How to assign dynamically an event handler without overwriting the existing event handler?

  - by user193655

  I need to loop through Components and assign an event handler (for example Dynamically assigning OnClick event for all TButton to ShowMessage('You clicked on ' + (Sender as TButton).Name); The problem is that in some cases I alreasy assigned the TButton OnClick event. Is there a way to solve the problem? Let's imagine I have Button1 for which the harcoded onclick event handler is: ShowMessage('This is Button1'); After my "parsing" I would like that the full event handler for Button1 becomes: ShowMessage('This is Button1'); // design time event handler code ShowMessage('You clicked on ' + (Sender as TButton).Name); // runtime added Note: I am looking for a soliution that allows me to use TButton as it is without inheriting from it.

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• SQL Select between two fields depending on the value of one field

  - by Filip

  Hi. I am using a PostgreSQL database, and in a table representing some measurements I've two columns: measurement, and interpolated. In the first I've the observation (measurement), and b is the interpolated value depending on nearby values. Every record with an original value has also an interpolated value. However, there are a lot of records without "original" observations (NULL), hence the values are interpolated and stored in the second column. So basically there are just two cases in the database: Value Value NULL Value Of course, it is preferable to use the value from the first column if available, hence I need to build a query to select the data from the first column, and if not available (NULL), then the database returns the value from the second column for the record in question. I have no idea how to build the SQL query. Please help. Thanks.

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• Factory Method Using Is/As Operator

  - by Swim

  I have factory that looks something like the following snippet. Foo is a wrapper class for Bar and in most cases (but not all), there is a 1:1 mapping. As a rule, Bar cannot know anything about Foo, yet Foo takes an instance of Bar. Is there a better/cleaner approach to doing this? public Foo Make( Bar obj ) { if( obj is Bar1 ) return new Foo1( obj as Bar1 ); if( obj is Bar2 ) return new Foo2( obj as Bar2 ); if( obj is Bar3 ) return new Foo3( obj as Bar3 ); if( obj is Bar4 ) return new Foo3( obj as Bar4 ); // same wrapper as Bar3 throw new ArgumentException(); } At first glance, this question might look like a duplicate (maybe it is), but I haven't seen one exactly like it. Here is one that is close, but not quite: http://stackoverflow.com/questions/242097/factory-based-on-typeof-or-is-a

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• boost variant static_visitor problem picking correct function

  - by Steve

  I'm sure I'm having a problem with template resolution here, but I'm not sure why I'm having the problem. I have a static visitor I'm passing to boost variant where i've had to do template specialization for certain cases. The case for everything except for MyClass should throw in the static_visitor below. Unfortunately, when the visitor is applied to pull a MyClass out, it selects the most generic case rather than the exact match. I would type each case explicitly, but that will be rather long. So, why is the compiler resolving the most generic case over the exact match, and is there anyway to fix it template<> class CastVisitor<MyClass>:public boost::static_visitor<MyClass> { public: template<typename U> MyClass operator()(const U & i) const { throw std::exception("Unable to cast"); } MyClass operator()(const MyClass& i) { return i; } };

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• Proper mechanism for sending PHP errors to the client

  - by Chris

  Greetings, I was trying to discover a proper way to send captured errors or business logic exceptions to the client in an Ajax-PHP system. In my case, the browser needs to react differently depending on whether a request was successful or not. However in all the examples I've found, only a simple string is reported back to the browser in both cases. Eg: if (something worked) echo "Success!"; else echo "ERROR: that failed"; So when the browser gets back the Ajax response, the only way to know if an error occurred would be to parse the string (looking for 'error' perhaps). This seems clunky. Is there a better/proper way to send back the Ajax response & notify the browser of an error? Thank you.

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• How to know if a PDF contains only images or has been OCR scanned for searching?

  - by Bratch

  I have a bunch of PDF files that came from scanned documents. The files contain a mix of images and text. Some were scanned as images with no OCR, so each PDF page is one large image, even where the whole page is entirely text. Others were scanned with OCR and contain images and searchable text where text is present. In many cases even words in the images were made searchable. I want to make an automated process to recognize the text in all of the scanned documents using OCR, with Acrobat 8 Pro, but I don't want to re-OCR the files that have already been through the OCR process in the past. Does anyone know if there is a way to tell which ones contain only images, and which ones already contain searchable text? I'm planning on doing this in C# or VB.NET but I don't think being able to tell the two kinds of files apart is language dependent.

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• Need complete picture of virtual adress space

  - by claws

  Hello, This image gives a good picture about Virtual Adress space. But it only says half of the story. It only gives complete picture of User Adress space ie.. lower 50% (or 75% in some cases). What about the rest 50% (or 25%) which is occupied by the kernel. I know kernel also has so many different things like kernel modules , device drivers, core kernel itself. There must be some kind of layout right? What is its layout? If you say its Operating System dependent. I would say, there are two major operating systems Windows & Linux. Please give answer for any one these.

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• Viewstate seems to be hijacked inadvertently

  - by dvr

  Hi, we are using asp.net 2.x, we use session state stored in sql server, 2 web servers in loadbalance, iis6. our issue is that in the last 3 months we have had 2 cases where some one using our enquiry form has seen someone else's info e.g. first name and last name. We are not populating the form from objects in session so I have come to the conclusion that the second user has somehow received the viewstate from the first user, after that user has tried to submit and got an error e.g. has posted view state and returned the the same page and the other user has requested that page at the same time (must have been on the same server I am guessing if it is a viewstate issue). have any of you experienced this before? some questions mulling around in my head is how does the worker process know to retun view state to a unique request and how does it determine a unique request etc..

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• regular expression for validation not working

  - by Camran

  I have a "description textarea" inside a form where user may enter a description for an item. This is validated with javascript before the form beeing submitted. One of the validation-steps is this: else if (!fld.value.match(desExp)){ And desExp: var desExp = /^\s*(\w[^\w]*){3}.*$/gm; Now my problem, this works fine on all cases except for descriptions where the description BEGINS with a special character of the swedish language (å, ä, ö). This wont work: åäö hello world But this will: hello world åäö Any fixes? Thanks

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• Easily digestible UI tips for developers

  - by David

  What are some key UI design tips that every developer should know? While there are a number of UI resources for developers (for example, Joel Spolsky's User Interface Design for Programmers), I'm interested in more of a bullet list that can be communicated in 1 to 2 pages. I'm interested in more tactical, day-to-day UI tips, as opposed to overarching UI design goals that would be covered in a UI design meeting (presumably attended by at least one person with a good UI sense). A collection of these tips might cover about 80% of the cases that an everyday programmer would come across.

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• In a Windows forms application, how can I use a listbox in a DataGridView coloumn instead of a combo

  - by Alex

  I'm working on a windows forms application that uses a DataGridView. Some of the cells contain a DataGridViewComboBox. In some cases, I have several values to display in the combobox. For that scenario, it would be better to use a ListBox instead of a ComboBox. Is it possible to use a multi-column listbox within a DataGridView instead of a ComboBox? If so, can you point me in the right direction? Thanks much. Al D.

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• C# - LINQ Including headache...

  - by ebb

  Case can have many Replies and one User, Replies can have one Case and one User, One User can have many Replies and many Cases. ObjectSet <= Case Object (IDbSet) ObjectSet.Include(x => x.User).Include(x => x.Replies).FirstOrDefault(x => x.Id == caseId); But the User Object for each Reply are not included? Only the User object for Case is Included? How would I include the User objects for the Replies too? Thanks in advance!

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• How to split row into multiple rows from the MySQL?

  - by user2818537

  I have a MySQL data table, in which I have more than 2 columns. First column has a unique value clinical trial value whereas second column has disease information. There are, in most of the cases, more than 2 disease names in one cell for a single id. I want to spilt those rows which cell contains two or more than two diseases. There is a pattern for searching also, i.e. small character is immediately followed by capital character., e.g. MalariaDengueTuberculosis like this. Suppose for these three diseases there is unique id, it should show like the following: NCT-ID disease 4534343654 Maleria 4534343654 Dengue 4534343654 Tubercoulsosis

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• Using ANTLR with Left-Recursive Rules

  - by CNevin561

  Basically Ive written a Parse for a language with just basic arithmetic operators ( +, -, * / ) etc, but for the minus and plus cases, the Abstract Syntax Tree which is generated has parsed them as right associative when they need to be left associative. Having a googled for a solution, i found a tutorial that suggests rewriting the rule from: Expression ::= Expression <operator> Term | Term as Expression ::= Term <operator> Expression*. However in my head this seems to generate the tree the wrong way round. Any pointers on a way to resolve this issue?

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• Zend Framework: How to handle exceptions in Ajax requests?

  - by understack

  Normally when an exception is thrown, Error controller takes command and displays error page with regular common header and footer. This behavior is not wanted in Ajax request. Because in case of error, whole html page is sent over. And in cases where I'm directly loading the content of http response in a div, this is even more unwanted. Instead in case of Ajax request, I just want to receive 'the actual error' thrown by exception. How can I do this? I think, one dirty way could be: set a var in ajax request and process accordingly. Not a good solution.

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• Are these 2 sql queries equivalent in all respects (e.g. estimated and actual execution plan)?

  - by Xerion

  Are query 1) == 2) in terms of estimated query plan AND actual plan? (can statistics affect the actual plan here, ever?) declare @cat int -- input param from prc ... 1) select * from A as a join B as b on b.id = a.id on b.cat = @cat join C as c on c.fid = b.fid on c.cat = @cat where a.cat = @cat 2) select * from A as a join B as b on b.id = a.id on b.cat = a.cat join C as c on c.fid = b.fid on c.cat = b.cat where a.cat = @cat It seems to me that these should logically be equivalent and the execution plan should always be the same regardless of actual difference in tables. And adding more conditions either in join, or where, or add more tables to join shouldn't change this. Are there cases this is not true?

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• 2 IP are stored for a visitor : PROXY ?

  - by Tristan

  Hello, on my database i've decided to store IP of the visitors who answoers to polls. It's all working, but there is only 2 cases where not only 1 IP is stored, but there is 2 SAME ip for the same visitor MySQLL output (i replaced 2 numbers by XX) 10.188.XX.129, 10.188.XX.129 Here's the script to recieve the IP of the visitor : <?php function realip() { if (isset($_SERVER)) { if (isset($_SERVER["HTTP_X_FORWARDED_FOR"])) { $realip = $_SERVER["HTTP_X_FORWARDED_FOR"]; } elseif (isset($_SERVER["HTTP_CLIENT_IP"])) { $realip = $_SERVER["HTTP_CLIENT_IP"]; } else { $realip = $_SERVER["REMOTE_ADDR"]; } } else { if ( getenv( 'HTTP_X_FORWARDED_FOR' ) ) { $realip = getenv( 'HTTP_X_FORWARDED_FOR' ); } elseif ( getenv( 'HTTP_CLIENT_IP' ) ) { $realip = getenv( 'HTTP_CLIENT_IP' ); } else { $realip = getenv( 'REMOTE_ADDR' ); } } return $realip; } ? Thanks

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• Simple php if query to double check

  - by skarama

  Is anything wrong with this code? <?php $variable = ; if (isset($variable)) { echo $variable ; echo "also this" ; } else echo "The variable is not set" ; ?> also, the other potential value of the variable is : $variable = <a href="http://www.mysite.com/article">This Article</a>; To clarify, I have a variable that may hold one of two possible values : an a href tag with it's url, or notihng at all. I need to have two different printouts for each of these cases, maybe I'm not doing it the right way though!

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• Use SQL to clone data in two tables that have a 1-1 relationship with each other

  - by AmoebaMan17

  Using MS SQL 2005, Table 1 ID | T1Value | T2ID | GroupID ---------------------------------- 1 | a | 10 | 1 2 | b | 11 | 1 3 | c | 12 | 1 4 | a | 22 | 2 Table 2 ID | T2Value ---------------- 10 | H 11 | J 12 | K 22 | H I want to clone the data for GroupID == 1 into a new GroupID so that I result with the following: Table 1 ID | T1Value | T2ID | GroupID ---------------------------------- 1 | a | 10 | 1 2 | b | 11 | 1 3 | c | 12 | 1 4 | a | 22 | 2 5 | a | 23 | 3 6 | b | 24 | 3 7 | c | 25 | 3 Table 2 ID | T2Value ---------------- 10 | H 11 | J 12 | K 22 | H 23 | H 24 | J 25 | K I've found some SQL clone patterns that allow me to clone data in the same table well... but as I start to deal with cloning data in two tables at the same time and then linking up the new rows correctly... that's just not something I feel like I have a good grasp of. I thought I could do some self-joins to deal with this, but I am worried in the cases where the non-key fields have the same data in multiple rows.

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