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• Is it wise to store a big lump of json on a database row

  - by Ieyasu Sawada

  I have this project which stores product details from amazon into the database. Just to give you an idea on how big it is: [{"title":"Genetic Engineering (Opposing Viewpoints)","short_title":"Genetic Engineering ...","brand":"","condition":"","sales_rank":"7171426","binding":"Book","item_detail_url":"http://localhost/wordpress/product/?asin=0737705124","node_list":"Books > Science & Math > Biological Sciences > Biotechnology","node_category":"Books","subcat":"","model_number":"","item_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=128","details_url":"http://localhost/wordpress/product/?asin=0737705124","large_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/large-notfound.png","medium_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/medium-notfound.png","small_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/small-notfound.png","thumbnail_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/thumbnail-notfound.png","tiny_img":"http://localhost/wordpress/wp-content/plugins/ecom/img/tiny-notfound.png","swatch_img":"http://localhost/wordpress/wp-content/plugins/ecom/img/swatch-notfound.png","total_images":"6","amount":"33.70","currency":"$","long_currency":"USD","price":"$33.70","price_type":"List Price","show_price_type":"0","stars_url":"","product_review":"","rating":"","yellow_star_class":"","white_star_class":"","rating_text":" of 5","reviews_url":"","review_label":"","reviews_label":"Read all ","review_count":"","create_review_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=132","create_review_label":"Write a review","buy_url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=19186","add_to_cart_action":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/add_to_cart.php","asin":"0737705124","status":"Only 7 left in stock.","snippet_condition":"in_stock","status_class":"ninstck","customer_images":["http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/31FIM-YIUrL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg","http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/51M2vvFvs2BL.jpg"],"disclaimer":"","item_attributes":[{"attr":"Author","value":"Greenhaven Press"},{"attr":"Binding","value":"Hardcover"},{"attr":"EAN","value":"9780737705126"},{"attr":"Edition","value":"1"},{"attr":"ISBN","value":"0737705124"},{"attr":"Label","value":"Greenhaven Press"},{"attr":"Manufacturer","value":"Greenhaven Press"},{"attr":"NumberOfItems","value":"1"},{"attr":"NumberOfPages","value":"224"},{"attr":"ProductGroup","value":"Book"},{"attr":"ProductTypeName","value":"ABIS_BOOK"},{"attr":"PublicationDate","value":"2000-06"},{"attr":"Publisher","value":"Greenhaven Press"},{"attr":"SKU","value":"G0737705124I2N00"},{"attr":"Studio","value":"Greenhaven Press"},{"attr":"Title","value":"Genetic Engineering (Opposing Viewpoints)"}],"customer_review_url":"http://localhost/wordpress/wp-content/ecom-customer-reviews/0737705124.html","flickr_results":["http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/5105560852_06c7d06f14_m.jpg"],"freebase_text":"No around the web data available yet","freebase_image":"http://localhost/wordpress/wp-content/plugins/ecom/img/freebase-notfound.jpg","ebay_related_items":[{"title":"Genetic Engineering (Introducing Issues With Opposing Viewpoints), , Good Book","image":"http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/140.jpg","url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=12165","currency_id":"$","current_price":"26.2"},{"title":"Genetic Engineering Opposing Viewpoints by DAVID BENDER - 1964 Hardcover","image":"http://localhost/wordpress/wp-content/uploads/2013/10/ecom_images/140.jpg","url":"http://localhost/wordpress/wp-content/ecom-plugin-redirects/ecom_redirector.php?id=130","currency_id":"AUD","current_price":"11.99"}],"no_follow":"rel=\"nofollow\"","new_tab":"target=\"_blank\"","related_products":[],"super_saver_shipping":"","shipping_availability":"","total_offers":"7","added_to_cart":""}] So the structure for the table is: asin title details (the product details in json) Will the performance suffer if I have to store like 10,000 products? Is there any other way of doing this? I'm thinking of the following, but the current setup is really the most convenient one since I also have to use the data on the client side: store the product details in a file. So something like ASIN123.json store the product details in one big file. (I'm guessing it will be a drag to extract data from this file) store each of the fields in the details in its own table field Thanks in advance!

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• Best approach for a clinic database

  - by user18013

  As a practical assignment for the database course I'm taking I've been instructed to create a database for a local clinic, I've meet with the doctors a couple of times and discussed the information that needs to be stored in the database from personal to medical. Now I'm facing a tough decision because I've been given two choices: either to implement the database as a "local website" which only operates inside the clinic via WiFi, or to implement the front-end as a regular desktop application connecting to a shared database. Note: I've a 40 days deadline to deliver the first prototype and meet with my client. My questions are: 1- which approach should I go with given that I've more experience with desktop applications programming than web? 2- if I go with desktop front-ends what would be the best way to synchronize the database between all clients?? I've no experience and having searched for an answer a lot but came up with nothing detailed on this matter. 3- if I go with the web solution which choice would be best PHP & MySQL or ASP.NET & SQL Server or a different combination?? (given that my knowledge in both PHP & ASP.NET are nearly the same).

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• In C what is the difference between null and a new line character? Guys help please [migrated]

  - by Siddhartha Gurjala

  Whats the conceptual difference and similarity between NULL and a newline character i.e between '\0' and '\n' Explain their relevance for both integer and character data type variables and arrays? For reference here is an example snippets of a program to read and write a 2d char array PROGRAM CODE 1: int main() { char sort(),stuname(),swap(),(*p)(),(*q)(); int n; p=stuname; q=swap; printf("Let the number of students in the class be \n"); scanf("%d",&n); fflush(stdin); sort(p,q,n); return 0; } char sort(p1,q1,n1) char (*p1)(),(*q1)(); int n1; { (*p1)(n1); (*q1)(); } char stuname(int nos) // number of students { char name[nos][256]; int i,j; printf("Reading names of %d students started--->\n\n",nos); name[0][0]='k'; //initialising as non NULL charecter for(i=0;i<nos;i++) // nos=number of students { printf("Give name of student %d\n",i); for(j=0;j<256;j++) { scanf("%c",&name[i][j]); if(name[i][j]=='\n') { name[i][j]='\0'; j=257; } } } printf("\n\nWriting student names:\n\n"); for(i=0;i<nos;i++) { for(j=0;j<256&&name[i][j]!='\0';j++) { printf("%c",name[i][j]); } printf("\n"); } } char swap() { printf("Will swap shortly after getting clarity on scanf and %c"); } The above code is working good where as the same logic given with slight diff is not giving appropriate output. Here's the code PROGRAM CODE 2: #include<stdio.h> int main() { char sort(),stuname(),swap(),(*p)(),(*q)(); int n; p=stuname; q=swap; printf("Let the number of students in the class be \n"); scanf("%d",&n); fflush(stdin); sort(p,q,n); return 0; } char sort(p1,q1,n1) char (*p1)(),(*q1)(); int n1; { (*p1)(n1); (*q1)(); } char stuname(int nos) // number of students { char name[nos][256]; int i,j; printf("Reading names of %d students started--->\n\n",nos); name[0][0]='k'; //initialising as non NULL charecter for(i=0;i<nos;i++) // nos=number of students { printf("Give name of student %d\n",i); ***for(j=0;j<256&&name[i][j]!='\0';j++)*** { scanf("%c",&name[i][j]); /*if(name[i][j]=='\n') { name[i][j]='\0'; j=257; }*/ } } printf("\n\nWriting student names:\n\n"); for(i=0;i<nos;i++) { for(j=0;j<256&&name[i][j]!='\0';j++) { printf("%c",name[i][j]); } printf("\n"); } } char swap() { printf("Will swap shortly after getting clarity on scanf and %c"); } Here one more instance of same program not giving proper output given below PROGRAM CODE 3: #include<stdio.h> int main() { char sort(),stuname(),swap(),(*p)(),(*q)(); int n; p=stuname; q=swap; printf("Let the number of students in the class be \n"); scanf("%d",&n); fflush(stdin); sort(p,q,n); return 0; } char sort(p1,q1,n1) char (*p1)(),(*q1)(); int n1; { (*p1)(n1); (*q1)(); } char stuname(int nos) // number of students { char name[nos][256]; int i,j; printf("Reading names of %d students started--->\n\n",nos); name[0][0]='k'; //initialising as non NULL charecter for(i=0;i<nos;i++) // nos=number of students { printf("Give name of student %d\n",i); ***for(j=0;j<256&&name[i][j]!='\n';j++)*** { scanf("%c",&name[i][j]); /*if(name[i][j]=='\n') { name[i][j]='\0'; j=257; }*/ } name[i][i]='\0'; } printf("\n\nWriting student names:\n\n"); for(i=0;i<nos;i++) { for(j=0;j<256&&name[i][j]!='\0';j++) { printf("%c",name[i][j]); } printf("\n"); } } char swap() { printf("Will swap shortly after getting clarity on scanf and %c"); } Why the program code 2 and program code 3 are not working as expected as that of the code 1?

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• Is Debug.Assert obsolete if you write unit tests?

  - by Justin Pihony

  Just like the question asks, is there a need to add Debug.Assert into your code if you are writing unit tests (which has its own assertions)? I could see that this might make the code more obvious without having to go into the tests, however it just seems that you might end up with duplicated asserts. It seems to me that Debug.Assert was helpful before unit-testing became more prevalent, but is now unnecessary. Or, am I not thinking of some use case?

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• Database design and performance impact

  - by Craige

  I have a database design issue that I'm not quite sure how to approach, nor if the benefits out weigh the costs. I'm hoping some P.SE members can give some feedback on my suggested design, as well as any similar experiences they may have came across. As it goes, I am building an application that has large reporting demands. Speed is an important issue, as there will be peak usages throughout the year. This application/database has a multiple-level, many-to-many relationship. eg object a object b object c object d object b has relationship to object a object c has relationship to object b, a object d has relationship to object c, b, a Theoretically, this could go on for unlimited levels, though logic dictates it could only go so far. My idea here, to speed up reporting, would be to create a syndicate table that acts as a global many-to-many join table. In this table (with the given example), one might see: +----------+-----------+---------+ | child_id | parent_id | type_id | +----------+-----------+---------+ | b | a | 1 | | c | b | 2 | | c | a | 3 | | d | c | 4 | | d | b | 5 | | d | a | 6 | +----------+-----------+---------+ Where a, b, c and d would translate to their respective ID's in their respective tables. So, for ease of reporting all of a which exist on object d, one could query SELECT * FROM `syndicates` ... JOINS TO child and parent tables ... WHERE parent_id=a and type_id=6; rather than having a query with a join to each level up the chain. The Problem This table grows exponentially, and in a given year, could easily grow past 20,000 records for one client. Given multiple clients over multiple years, this table will VERY quickly explode to millions of records and beyond. Now, the database will, in time, be partitioned across multiple servers, but I would like (as most would) to keep the number of servers as low as possible while still offering flexibility. Also writes and updates would be exponentially longer (though possibly not noticeable to the end user) as there would be multiple inserts/updates/scans on this table to keep it in sync. Am I going in the right direction here, or am I way off track. What would you do in a similar situation? This solution seems overly complex, but allows the greatest flexibility and fastest read-operations. Sidenote 1 - This structure allows me to add new levels to the tree easily. Sidenote 2 - The database querying for this database is done through an ORM framework.

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• A talk about observer pattern

  - by Martin

  As part of a university course I'm taking, I have to hold a 10 minute talk about the observer pattern. So far these are my points: What is it? (defenition) Polling is an alternative Polling VS Observer When Observer is better When Polling is better (taken from here) A statement that Mediator pattern is worth checking out. (I won't have time to cover it in 10 minutes) I would be happy to hear about: Any suggestions to add something? Another alternative (if exists)

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• How can i be sure that professional programming is not for me ?

  - by user17766

  Hello everybody I love programming, developing projects for hobby and learning new concepts. I am getting harder too much in current job Despite learnt many thing well. I can even hardly understand assigned tasks. I am asking why i am getting harder to myself. It may not my fault? Our architecture doesn't spend enough time to explain complicated sides of project for us or i am not enough smart one for understand fastly. Our architecture also doesn't know what kind of hell he is creating ? Seeing 3 level generic types and 4-5 level generic inheritance in domain model objects hell makes me think so really. It looks abusing concepts more than reduce complexity. Thinking that he hasn't experienced before such a big project while he is getting confused in problems of the project. May i am not in right company ? May i am not good programmer ? May i am really stupid ? Become good in programming concepts is not enough to deal big project's complications so someone should to tell me that i have to still effort too much even i am good programmer for adopting myself to any big project ? Also i had another bad experiences from previous job but my professional experiences is almost few months but i spend 2 years for learning and coding for fun and i really can say that i have well skills on OOP, Design Patterns, coding standards and deep knowledge in language currently used. Sometimes i am thinking to leave programming professionally and work in any lame job while doing programming just for hobby. Waiting suggestions and insights

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• Programming Test

  - by Travis Webb

  We are looking to hire some more Java developers onto our team, and plan to test their coding abilities with a test. We currently use a web-based Java test that automatically compiles and runs the code, but it is very flaky and we're having problems with our candidates losing their work on this site. Not only is this frustrating for everyone, it makes us look like we don't know what we're doing. Is there a popular testing suite out there? What do you use? I'm not interested in dogmatic arguments on whether or not I should be testing my candidates in this way, I'm looking for a tool that will help me do it.

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• Getting from a user-story to code while using TDD (scrum)

  - by Ittai

  I'm getting into scrum and TDD and I think I have some confusion which I'd like to get your feedback about. Let's assume I have a user-story in my backlog, in order for me to start developing it as part of TDD I need to have requirements, right so far? Is it true to say that the product manager and the QA should be responsible for taking the user-story and breaking it down to acceptance tests? I think the above is true since the acceptance tests need to be formal, so they can be used as tests, but also human readable so that the product can approve they are the requirements, right? Is it also true that I later take these acceptance tests and use them as my requirements, i.e. they are a set of use-cases which I implement (through TDD)? I hope I'm not making too much of a mess but that's the current flow I have in mind right now. Update I think my initial intentions were unclear so I'll try to rephrase. I want to know more details about the scrum flow of turning a user-story into code while using TDD. The starting point is obvious, a user surfaces a need (or the user's representative as the product) which is a short 1-2 lines description in the known format and that is added to the product backlog. When there is a spring planning meeting user-stories are taken from the backlog and assigned to developers. In order for a developer to write code they need requirements (especially in TDD since the requirements are what the tests are derived from). When, by whom and to which format are the requirements compiled? What I had in mind was that the product and QA define the requirements via acceptance tests (I'm thinking of automatic using FitNesse or the sort but that's not the core I think) which help to serve 2 purposes at the same time: They define "Done" properly. They give a developer something to derive tests from. I wasn't sure when these were written (before the sprint they're picked then that might be a waste since additional information will arrive or the story won't be picked, during the iteration then the developer might get stuck waiting for them...)

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• Developing JSON API for a Carpool Engine

  - by Siddharth

  I am developing a new set of API methods for carpooling/cab booking, so if a developer needs to develop an app or webportal for carpooling, he can call my JSON API. Basically making it easy for developers. My API current has: AddVehicle AddJourney SearchJourney SubscribeToThisJourney(journey) SubscriberList(journey) to get list of people who have subscribed for this journey AcceptSubscription(subscriber) AcceptedSubcriberList SubscriberList to get list of providers I have subscribed to I need help with replacing subscriber with something else. It's difficult to remember, and confusing when you see 3 methods that mean very different things: SubscriberList, SubscribedToThisJourneyList and AcceptedSubscriberList. Confusing to remember. One is a list of who I have subscribed to Who has subscribed to me Whose subscription I have accepted How can I name these methods to make them easier to understand and remember?

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• Architecture advice for converting biz app from old school to new school?

  - by Aaron Anodide

  I've got a WinForms business application that evolved over the past few years. It's forms over data with a number custom UI experiences taylored to the business, so I don't think it's a candidate to port to something like SharePoint or re-write in LightSwitch (at least not without significant investment). When I started it in 2009 I was new to this type of development (coming from more low level programming and my RDBMS knowledge was just slightly greater than what I got from school). Thus, when I was confronted with a business model that operates on a strict monthly accounting cycle, I made the unfortunate decision to create a separate database for each accounting period. Also, when I started I knew DataSets, then I learned Linq2Sql, then I learned EntityFramework. The screens are a mix and match of those. Now, after a few years developing this thing by myself I've finally got a small team. Ultimately, I want a web front end (for remote access to more straight up screens with grids of data) and a thick client (for the highly customized interfaces). My question is: can you offer me some broad strokes architecture advice that will help me formulate a battle plan to convert over to a single database and lay the foundations for my future goals at the same time? Here's a screen shot showing how an older screen uses DataSets and a newer screen uses EF (I'm thinking this might make it more real for someone reading the question - I'm willing to add any amount of detail if someone is willing to help).

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• How to name an subclass that add a minor, detailed thing?

  - by Louis Rhys

  What is the most concise (yet descriptive) way of naming a subclass that only add a specific minor thing to the parent? I encountered this case a lot in WPF, where sometime I have to add a small functionality to an out-of-the-box control for specific cases. Example: TreeView doesn't change the SelectedItem on right-click, but I have to make one that does in my application. Some possible names are TreeViewThatChangesSelectedItemOnRightClick (way too wordy and maybe difficult to read because there is so many words concantenated together) TreeView_SelectedItemChangesOnRightClick (slightly more readable, but still too wordy and the underscore also breaks the normal convention for class names) TreeViewThatChangesSIOnRC (non-obvious acronym), ExtendedTreeView (more concise, but doesn't describe what it is doing. Besides, I already found a class called this in the library, that I don't want to use/modify in my application). LouisTreeView, MyTreeView, etc. (doesn't describe what it is doing). It seems that I can't find a name which sounds right. What do you do in situation like this?

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• What are the best resources for learning about concurrency and multi-threaded applications?

  - by Zepee

  I realised I have a massive knowledge gap when it comes to multi-threaded applications and concurrent programming. I've covered some basics in the past, but most of it seems to be gone from my mind, and it is definitely a field that I want, and need, to be more knowledgeable about. What are the best resources for learning about building concurrent applications? I'm a very practical oriented person, so if said book contains concrete examples the better, but I'm open to suggestions. I personally prefer to work in pseudocode or C++, and a slant toward game development would be best, but not required.

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• Are CK Metrics still considered useful? Is there an open source tool to help?

  - by DeveloperDon

  Chidamber & Kemerer proposed several metrics for object oriented code. Among them, depth of inheritance tree, weighted number of methods, number of member functions, number of children, and coupling between objects. Using a base of code, they tried to correlated these metrics to the defect density and maintenance effort using covariant analysis. Are these metrics actionable in projects? Perhaps they can guide refactoring. For example weighted number of methods might show which God classes needed to be broken into more cohesive classes that address a single concern. Is there approach superseded by a better method, and is there a tool that can identify problem code, particularly in moderately large project being handed off to a new developer or team?

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• How can Swift be so much faster than Objective-C?

  - by Yellow

  Apple launched its new programming language Swift today. In the presentation, they made some performance comparisons between Objective-C and Python. The following is a picture of one of their slides, of a comparison of those three languages performing some complex object sort: There was an even more incredible graph about a performance comparison working on some encryption algorithm. Obviously this is a marketing talk, and they didn't go into detail on how this was implemented in each. I leaves me wondering though: how can a new programming language be so much faster? In this example, surely you just have a bad Objective-C compiler or you're doing something in a less efficient way? How else would you explain a 40% performance increase? I understand that garbage collection/automated reference control might produce some additional overhead, but this much?

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• Data structure: sort and search effectively

  - by Jiten Shah

  I need to have a data structure with say 4 keys . I can sort on any of these keys. What data structure can I opt for? Sorting time should be very little. I thought of a tree, but it will be only help searching on one key. For other keys I'll have to remake the tree on that particular key and then find it. Is there any data structure that can take care of all 4 keys at the same time? these 4 fields are of total 12 bytes and total size for each record - 40 bytes.. have memory constraints too... operations are : insertion, deletion, sorting on different keys.

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• Best Books of C

  - by Patrick

  Hi, I realy want to get high skills in C programming and I know that the best and only way is hard work and lots of practice. though I found so many tutorials and books available on the net about learning the C language. I'm just looking for one or two good books in C that I can learn from and get high skills in C. Anyone knows such a great book/books for C programming pls? (sorry for replication if the question exists already in the forum) Regards!

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• Is software development an engineering discipline?

  - by Vaibhav Garg

  Can software development be considered engineering? If no, what are the things that it lacks in order to be qualified as an engineering discipline? Related to this is this question on Stack Overflow about the difference between a programmer and a software engineer. There is the Software Engineering Institute at Carnigie Mellon University that prescribes and maintains the CMMI standards. Is this something that will turn development into engineering?

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• Is it necessary to read every single byte to check if a copied file is identical to the original?

  - by Koen027

  I recently learned of a program called Total Commander. It's a Windows Explorer replacement and has its own stuff to copy files. To check whether the files are identical, instead of calculation a CRC, it literally checks every single byte, one at a time, on both the original and the copy. My question is: Is this necessary? Can CRC or any other such technique go wrong? Should you, as a programmer, try and implement this perfect but slow system, or is it too extreme?

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• When to use shared libraries for a web framework?

  - by CamelBlues

  tl;dr: I've found myself hosting a bunch of sites running on the same web framework (symfony 1.4). Would it be helpful if I moved all of the shared library code into the same directory and shared it across the sites? more I see some advantages to this: Each site takes up less disk space Library updates (an unlikely scenario) can take place across all sites I also see some disadvantages, mostly in terms of a single point of failure and the inability to have sites using different versions of the framework. My real concern, though, is performance. I hypothesize that I will see a performance increase, since the PHP code will already be cached for all sites when they call the framework. Is this a correct hypothesis?

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• Benefit of using Data URI to embed images within HTML document and its cross-browser compatibility

  - by Manoj Agarwal

  I want to embed an image using Data URI within HTML document so that we don't need image as a separate attachment, we get just one HTML file that contains the actual image. What are its advantages and disadvantages? Does IE10 supports it? Is it useful to have such an implementation? I am working on an application, where we have html documents that link towards images stored in some location. If I use tiny online editor, as images are saved somewhere in the server, while editing the document, i can provide a link towards that image, but can't preview the final document with images from within tiny editor. If I chose to download the file locally, then i will need to download the images from server side. It looks a bit overkill, so I thought if Data URI could be used in such a situation.

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• Is eval the defmacro of javascript?

  - by Florian Margaine

  In Common Lisp, defmacro basically allows us to build our own DSL. I read this page today and it explains something cleverly done: But I wasn't about to write out all these boring predicates myself, so I defined a function that, given a list of words, builds up the text for such a predicate automatically, and then evals it to produce a function. Which just looks like defmacro to me. Is eval the defmacro of javascript? Could it be used as such?

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• Messaging technologies between applications ?

  - by Samuel

  Recently, I had to create a program to send messages between two winforms executable. I used a tool with simple built-in functionalities to prevent having to figure out all the ins and outs of this vast quantity of protocols that exist. But now, I'm ready to learn more about the internals difference between each of theses protocols. I googled a couple of them but it would be greatly appreciate to have a good reference book that gives me a clean idea of how each protocol works and what are the pros and cons in a couple of context. Here is a list of nice protocols that I found: Shared memory TCP List item Named Pipe File Mapping Mailslots MSMQ (Microsoft Queue Solution) WCF I know that all of these protocols are not specific to a language, it would be nice if example could be in .net. Thank you very much.

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• Merge sort versus quick sort performance

  - by Giorgio

  I have implemented merge sort and quick sort using C (GCC 4.4.3 on Ubuntu 10.04 running on a 4 GB RAM laptop with an Intel DUO CPU at 2GHz) and I wanted to compare the performance of the two algorithms. The prototypes of the sorting functions are: void merge_sort(const char **lines, int start, int end); void quick_sort(const char **lines, int start, int end); i.e. both take an array of pointers to strings and sort the elements with index i : start <= i <= end. I have produced some files containing random strings with length on average 4.5 characters. The test files range from 100 lines to 10000000 lines. I was a bit surprised by the results because, even though I know that merge sort has complexity O(n log(n)) while quick sort is O(n^2), I have often read that on average quick sort should be as fast as merge sort. However, my results are the following. Up to 10000 strings, both algorithms perform equally well. For 10000 strings, both require about 0.007 seconds. For 100000 strings, merge sort is slightly faster with 0.095 s against 0.121 s. For 1000000 strings merge sort takes 1.287 s against 5.233 s of quick sort. For 5000000 strings merge sort takes 7.582 s against 118.240 s of quick sort. For 10000000 strings merge sort takes 16.305 s against 1202.918 s of quick sort. So my question is: are my results as expected, meaning that quick sort is comparable in speed to merge sort for small inputs but, as the size of the input data grows, the fact that its complexity is quadratic will become evident? Here is a sketch of what I did. In the merge sort implementation, the partitioning consists in calling merge sort recursively, i.e. merge_sort(lines, start, (start + end) / 2); merge_sort(lines, 1 + (start + end) / 2, end); Merging of the two sorted sub-array is performed by reading the data from the array lines and writing it to a global temporary array of pointers (this global array is allocate only once). After each merge the pointers are copied back to the original array. So the strings are stored once but I need twice as much memory for the pointers. For quick sort, the partition function chooses the last element of the array to sort as the pivot and scans the previous elements in one loop. After it has produced a partition of the type start ... {elements <= pivot} ... pivotIndex ... {elements > pivot} ... end it calls itself recursively: quick_sort(lines, start, pivotIndex - 1); quick_sort(lines, pivotIndex + 1, end); Note that this quick sort implementation sorts the array in-place and does not require additional memory, therefore it is more memory efficient than the merge sort implementation. So my question is: is there a better way to implement quick sort that is worthwhile trying out? If I improve the quick sort implementation and perform more tests on different data sets (computing the average of the running times on different data sets) can I expect a better performance of quick sort wrt merge sort? EDIT Thank you for your answers. My implementation is in-place and is based on the pseudo-code I have found on wikipedia in Section In-place version: function partition(array, 'left', 'right', 'pivotIndex') where I choose the last element in the range to be sorted as a pivot, i.e. pivotIndex := right. I have checked the code over and over again and it seems correct to me. In order to rule out the case that I am using the wrong implementation I have uploaded the source code on github (in case you would like to take a look at it). Your answers seem to suggest that I am using the wrong test data. I will look into it and try out different test data sets. I will report as soon as I have some results.

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• scrapy cannot find div on this website [on hold]

  - by Jaspal Singh Rathour

  I am very new at this and have been trying to get my head around my first selector can somebody help? i am trying to extract data from page http://groceries.asda.com/asda-webstore/landing/home.shtml?cmpid=ahc--ghs-d1--asdacom-dsk-_-hp#/shelf/1215337195041/1/so_false all the info under div class = listing clearfix shelfListing but i cant seem to figure out how to format response.xpath(). I have managed to launch scrapy console but no matter what I type in response.xpath() i cant seem to select the right node. I know it works because when I type response.xpath('//div[@class="container"]') I get a response but don't know how to navigate to the listsing cleardix shelflisting. I am hoping that once i get this bit I can continue working my way through the spider. Thank you in advance! PS I wonder if it is not possible to scan this site - is it possible for the owners to block spiders?

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