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• Why is writing a compiler in a functional language so efficient and easier?

  - by wvd

  Hello all, I've been thinking of this question very long, but really couldn't find the answer on Google as well a similar question on Stackoverflow. If there is a duplicate, I'm sorry for that. A lot of people seem to say that writing compilers and other language tools in functional languages such as OCaml and Haskell is much more efficient and easier then writing them in imperative languages. Is this true? And if so -- why is so efficient and easy to write them in functional languages instead of in an imperative language, like C? Also -- isn't a language tool in a functional language slower then in some low-level language like C? Thanks in advance, William v. Doorn

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• How do I output an individual character when using char *[] = "something"

  - by Matt

  I've been playing with pointers to better understand them and I came across something I think I should be able to do, but can't sort out how. The code below works fine - I can output "a", "dog", "socks", and "pants" - but what if I wanted to just output the 'o' from "socks"? How would I do that? char *mars[4] = { "a", "dog", "sock", "pants" }; for ( int counter = 0; counter < 4; counter++ ) { cout << mars[ counter ]; } Please forgive me if the question is answered somewhere - there are 30+ pages of C++ pointer related question, and I spent about 90 minutes looking through them, as well as reading various (very informative) articles, before deciding to ask.

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• split with javascript

  - by Sourabh

  Hi below is something I am trying to do with JavaScript. If I have string like str = "how are you? hope you are doing good" ; now I want to split it with ? but I dont want to lose the "?". Instead I want to break the string just after the question mark such a way that question mark is with the first segment that we have after splitting str what should I get is ["how are you?","hope you are doing good"] I am not sure if it can be done with Javascript split() function ,please help.

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• Can a constructor in java can be private?

  - by Rajesh

  If the answer for my question is yes, then what is the use of having a private constructor.

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• Codesample with bufferoverflow (gets method). Why does it not behave as expected?

  - by citronas

  This an extract from an c program that should demonstrate a bufferoverflow. void foo() { char arr[8]; printf(" enter bla bla bla"); gets(arr); printf(" you entered %s\n", arr); } The question was "How many input chars can a user maximal enter without a creating a buffer overflow" My initial answer was 8, because the char-array is 8 bytes long. Although I was pretty certain my answer was correct, I tried a higher amount of chars, and found that the limit of chars that I can enter, before I get a segmentation fault is 11. (Im running this on A VirtualBox Ubuntu) So my question is: Why is it possible to enter 11 chars into that 8 byte array?

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• Can a pointer ever point to itself?

  - by eSKay

  This question was mentioned here. My doubt is: If a pointer variable has the same address as its value, is it really pointing to itself? For example - in the following piece of code, is a a pointer to itself? #include<stdio.h> int main(){ int* a; int b = (int)&a; a = b; printf("address of a = %d\n", &a); printf(" value of a = %d\n", a); } If a is not a pointer to itself, then the same question poses again: Can a pointer point to itself? Also, how is a self pointing pointer useful?

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• Filtering out unique rows in MySQL

  - by jpatokal

  So I've got a large amount of SQL data that looks basically like this: user | src | dst 1 | 1 | 1 1 | 1 | 1 1 | 1 | 2 1 | 1 | 2 2 | 1 | 1 2 | 1 | 3 I want to filter out pairs of (src,dst) that are unique to one user (even if that user has duplicates), leaving behind only those pairs belonging to more than one user: user | src | dst 1 | 1 | 1 1 | 1 | 1 2 | 1 | 1 In other words, pair (1,2) is unique to user 1 and pair (1,3) to user 2, so they're dropped, leaving behind only all instances of pair (1,1). Any ideas? The answers to the question below can find the non-unique pairs, but my SQL-fu doesn't suffice to handle the complication of requiring that they belong to multiple users as well. [SQL question] How to select non "unique" rows

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• Get client timezone (not GMT offset amount) in JS

  - by Rex M

  I need to determine the client timezone (e.g. CET, GMT, EST) in JS. Getting the offset is straightforward, but doesn't have all the info necessary to determine the TZ, at least not easily. I have a feeling it might be possible to use a combination of offset, whether DST is in use and in effect, etc. but I'm hoping someone else has done the work already, especially considering the weird exceptions when dealing with time. This question is similar but both the question and the answer are based on the (incorrect) assumption every browser's DateString format includes the name of the timezone - which it does not. That is an implementation detail. So, with that I am currently stuck.

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• An exception to the "only one implementation" rule ?

  - by ereOn

  While I was reading the accepted answer of this question, I had the following question: Typically, methods are defined in header files (.hpp or whatever), and implementation in source files (.cpp or whatever). One of the main reasons it is bad practice to ever include a "source file" (#include <source_file.cpp>) is that its methods implementation would then be duplicated, resulting in linking errors. When one writes: #ifndef BRITNEYSPEARS_HPP #define BRITNEYSPEARS_HPP class BritneySpears { public: BritneySpears() {}; // Here the constructor has implementation. }; #endif /* BRITNEYSPEARS_HPP */ He is giving the implementation of the constructor (here an "empty" implementation, but still). But why then including this header file multiple times (aka. on different source files) will not generate a "duplicate definition" error at link time ?

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• Do Managers in Python Multiprocessing module lock the shared data?

  - by AnonProcess

  This Question has been asked before: http://stackoverflow.com/questions/2936626/how-to-share-a-dictionary-between-multiple-processes-in-python-without-locking However I have several doubts regarding the program given in the answer: The issue is that the following step isn't atomic d['blah'] += 1 Even with locking the answer provided in that question would lead to random results. Since Process 1 read value of d['blah'] saves it on the stack increments it and again writes it. In Between a Process 2 can read the d['blah'] as well. Locking means that while d['blah'] is being written or read no other process can access it. Can someone clarify my doubts?

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• How long does a MailItem.Property[myProperty] live?

  - by Darien Ford

  I'm writing a TransportAgent for Exchange and want to tag a MailItem with some identifying information. The MailItem class seems to have this functionality with the MailItem.Properties property; however, my question is to the length of time an entry would remain available. e.g. e.MailItem.Properties.Add(new KeyValuePair<string,object>("MyKey", "myValue")); After this MailItem is delivered to the correct mailbox, if someone were to reply to the email, would the newly created reply retain that set value? I think while writing this question out I have answered it for myself (which rationally would be no) but any practical experience and insight would be appreciated.

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• How to format a getUpdatedAt() kind of date in Symfony?

  - by Guillaume Flandre

  I'd like to change the formatting of a date in Symfony 1.4 The default one being: <?php echo $question->getUpdatedAt(); // Returns 2010-01-26 16:23:53 ?> I'd like my date to be formatted like so: 26/01/2010 - 16h23 I tried using the format_date helper DateHelper class. Unfortunately the API is rather empty (something really needs to be done about it.) Browsing the helper's source code, I found that a second argument, format, can be passed. I assumed it was using the same syntax as PHP's date function. But here's what it outputs (same example as above): <?php sfContext::getInstance()->getConfiguration()->loadHelpers('Date'); // [...] echo format_date($question->getUpdatedAt(),'d/m/y - H\hi') // Returns 26/23/2010 - 16\4i I'm sure I'm not the first one having trouble doing this but I've been Googling around and nothing accurate showed up. Do you guys have any idea how to format a date in Symfony 1.4?

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• Where is the best place to put <script> tags in HTML markup?

  - by mipadi

  When embedding JavaScript in an HTML document, where is the best place to put the <script> tags and included JavaScript? I seem to recall that you are not supposed to place these in the <head> section, but placing at the beginning of the <body> section is bad, too, since the JavaScript will have to be parsed before the page is rendered completely (or something like that). This seems to leave the end of the <body> section as a logical place for <script> tags. So, where is the best place to put the <script> tags? (This question references this question, in which it was suggested that JavaScript function calls should be moved from <a> tags to <script> tags. I'm specifically using JQuery, but more general answers are also appropriate.)

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• Why input elements don't render the value passed in ASP.Net MVC?

  - by MediaSlayer

  This post asks this question but doesn't really give an answer, so I thought I would ask the question differently. I have a page that renders a hidden value from the model: <%=Html.Hidden("myName", model.myValue) %> Since I am passing a value in the value parameter, you would think it would output that value, but it doesn't. The code for rendering input fields has the following: string attemptedValue = (string)htmlHelper.GetModelStateValue(name, typeof(string)); tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(name) : valueParameter), isExplicitValue); Basically, if the ModelState (which contains posted values) contains a value for the "name" passed, it will use that value instead of your passed value to the helper method. In my case, I updated the model and my updated value wasn't outputted. If I pass a value to a method, I expect that value to be rendered. Am I missing something in this design or is it just wrong?

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• Why is writing a compiler in a functional language easier?

  - by wvd

  Hello all, I've been thinking of this question very long, but really couldn't find the answer on Google as well a similar question on Stackoverflow. If there is a duplicate, I'm sorry for that. A lot of people seem to say that writing compilers and other language tools in functional languages such as OCaml and Haskell is much more efficient and easier then writing them in imperative languages. Is this true? And if so -- why is it so efficient and easy to write them in functional languages instead of in an imperative language, like C? Also -- isn't a language tool in a functional language slower then in some low-level language like C? Thanks in advance, William v. Doorn

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• mysql varchar innodb page size limit 8100 bytes

  - by David19801

  Hi, Regarding innodb, someone recently told me: "the varchar content beyond 768 bytes is stored in supplemental 16K pages" This is very interesting. If each varchar will be latin1, which I believe stores as 1byte per letter, would a single varchar(500) (<768 bytes) require an extra i/o as a varchar(1000) (768 bytes) would?? (this question is to find out if all varchars or just big varchars are split into a separate page) Is the 768 limit per varchar or for all varchars in the row added together? (for example, does this get optimized - varchar(300), varchar(300), varchar(300): [where each individual varchar column is below 768 but together they are above 768 characters]? I am confused about if the 768 limit relates to each individual varchar or all varchars in the row totaled (as in the question). Any clarification? EDIT: Removed part about CHARS due to finding out about their limit of 255 max.

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• How to find the number of inversions in an array ?

  - by Michael

  This is an phone interview question: "Find the number of inversions in an array". I guess they mean O(N*log N) solution since O(N^2) is trivial. I guess it cannot be better than O(N*log N) since sorting is O(N*log N) I have checked a similar question from SO and can summarize the answers as follows: Calculate half the distance the elements should be moved to sort the array : copy the array and sort the copy. For each element of the original array a[i] find it's position j in the sorted copy (binary search) and sum abs(i - j)/2. Modify merge sort : modify merge to count inversions between two sorted arrays (it takes O(N)) and run merge sort with the modified merge. Does it make sense ? Are there other (maybe simpler) solution ? Isn't it too hard for a phone interview ?

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• Initialising structs in C++

  - by Neil Butterworth

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

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• Can I add and remove elements of enumeration at runtime in Java

  - by Brabster

  It is possible to add and remove elements from an enum in Java at runtime? For example, could I read in the labels and constructor arguments of an enum from a file? @saua, it's just a question of whether it can be done out of interest really. I was hoping there'd be some neat way of altering the running bytecode, maybe using BCEL or something. I've also followed up with this question because I realised I wasn't totally sure when an enum should be used. I'm pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.

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• OO C++ - Virtual Methods

  - by Phorce

  Just a really quick question here. I'm using virtual functions to read in from a text file. Now, it's virtual because in one aspect I want the values to be normalised, and, in the other respect I don't want them to be normalised. I have tried to do this: bool readwav(string theFile, 'native'); So in theory, if the 'native' is used, this method should be called, however, if 'double' is called then a different version of the method is called. Same for if the value is empty, it should just perform the native option. First question, why doesn't the declaration above work? Also, is this the best route to go down? Or, would it be better to have just one class method that switches between the options. Thanks :)

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• How to get attributes values separately for each container present on the webpage in jquery ?

  - by Rachel

  This question is in continuation to How to get attributes of container in jquer, I have different containers on my webpage and all of them have <div id = "some values"> now how can I get attributes values separately for each component ? Is there any way I can know which attribute id belong to which container div ? Currently I am using : var id = $( '.promotion' ).attr( 'id' ); But if I have multiple promotional components on page and all have same div attribute as id than how can I relate that this particular attribute id belonged to this specific container ? Update: I am having a function which is called for each container present on the page and so if I am using above mentioned code than will it not always return me the first match for id in the div and would never go to other divs and so I will always get same value for id which is for the first container ? If so than what is the work around for this ? Hope this question is clear.

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• How to Not alter font in webpage after opening a file (pdf or jpg) in ASP.NET C#? [closed]

  - by Victor

  Possible Duplicate: How to not alter font in webpage after opening a pdf in ASP.NET C#? Previously I posted this question: How to open files from a specific route in ASP-NET c#? in fact, I have already asked this however it was only a minor question so I guess it wasn't that important in the previous post, so I will ask here. Whenever I open a pdf with: Response.Write("<script>window.open('FilePath');</script>"); All of the font in the page is altered, example, the letter's size increases and some of the letter's colors are switched to black instead of the font that I assigned. Is there a way that I can work around that?? http://imageshack.us/a/img838/5145/beforeja.png http://imageshack.us/a/img546/4760/afterw.png Oh and I noticed that this also happens when you open images like jpg

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• How to indicate to user that a command affects a subset of a multiple selection?

  - by Zamboni

  Here is an example that illustrates my question. I have a program that lists 1000 items. I select 10 of 1000 items. The program enables a button indicating that a command is available for my selection. I click the button, and a window appears. I make some change in the window and click OK. The command changes 5 of the 10 items in my multiple selection, and those 5 changed items now reflect a modified state in my list. My question is: How do I indicate to user that the command affects a subset of a multiple selection before clicking OK? Can anyone cite examples of existing products that handle this scenario well?

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• POST and multiple submit buttons on form (iphone)

  - by Jonathan

  NSString *reqURL = [NSString stringWithFormat:@"%@/login",SERVER_URL]; NSMutableURLRequest *req = [[NSMutableURLRequest alloc]initWithURL:[NSURL URLWithString:reqURL]]; [req setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"content-type"]; NSData *myRequestData = [NSData dataWithBytes:[@"username=whatever&password=whatever" UTF8String] length: [@"username=whatever&password=whatever" length]]; [req setHTTPMethod: @"POST"]; [req setHTTPBody: myRequestData]; NSData *returnData = [NSURLConnection sendSynchronousRequest:req returningResponse: nil error: nil]; NSString *html = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding]; I got this code from another question I asked. But what happens if there is more than one submit button. I really have no idea how to ask this question. An example of such situation is on the logout page for this site. There are no fields to enter data into, but there are 2 submit buttons. How can I "simulate clicking" on one of those buttons using code like the above (so not using a UIWebView)

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• Additional information with widgets in django

  - by fromclouds

  I am displaying a django widget, with which I need to display additional information (something like a tool tip) that is attendant to the widget. I essentially have a widget that asks a random question, which is self contained. {{ form.fieldname }} displays the full widget which looks something like (à la the widget's render method): <label for="id_answer">Question:</label> <input type="hidden" name="question_id" value="n" /> <span class="prompt">What is the air-speed velocity of an unladen swallow?</span> <input type="text" name="answer" /> What I'm essentially asking is, is there a way to break out the prompt, so that I can lay the widget out piecemeal? I would like to lay it out not with a call to {{ form.fieldname }} as above, but like: {{ form.fieldname.label }} {{ form.fieldname.prompt }} {{ form.fieldname }} Does anyone know how to do this?

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