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  • How can HTML5 "replace" Flash?

    - by Kassini
    A topic of debate that's seen a resurgence since the unveiling of the iPad is the issue of Flash versus HTML5. There are those that suggest that HTML5 will one day supplant/replace Adobe Flash. I do not develop software that runs in a browser, so my (limited) understanding is: HTML is a pure-text markup language that is delivered over HTTP to a client browser. The client browser interprets the markup and renders (with varying degrees of success) the page according to an standard specification. Adobe Flash is a propriety framework for working with audio, video, sound and raster/vector graphics. It requires special authoring tools (a compiler perhaps?) and a custom player that's available as a plug-in to most common browsers. Could someone please explain (to this C/C++ developer) how it is possible from a technical/coding point-of-view that a text-based markup language (HTML5) could be considered a replacement to a multimedia framework (Flash)? Please no opinionated arguments - just technical facts.

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  • Which metadata I should save when downloading web-pages?

    - by Vojtech R.
    Hi, I'm going to download (for future purposes of language processing) some thousands webpages. Now I'm thinking, which metadata I should save. I explore this, but I do not wont to neglect something important. <title> <link> <publish_date> <date_downloaded> <source> // to this page <keyword> // for Solr indexing <text> // cleaned body of page Is there something important what I could miss in future?

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  • Are colons allowed URIs?

    - by Emanuil
    I thought using colons in URIs was "illegal". Then I saw that vimeo.com is using URIs like http://www.vimeo.com/tag:sample. What do you feel about the usage of colons in URIs? How do I make my Apache server work with the "colon" syntax because now it's throwing the "Access forbidden!" error when there is a colon in the first segment of the URI?

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  • When does invoking a member function on a null instance result in undefined behavior?

    - by GMan
    This question arose in the comments of a now-deleted answer to this other question. Our question was asked in the comments by STingRaySC as: Where exactly do we invoke UB? Is it calling a member function through an invalid pointer? Or is it calling a member function that accesses member data through an invalid pointer? With the answer deleted I figured we might as well make it it's own question. Consider the following code: #include <iostream> struct foo { void bar(void) { std::cout << "gman was here" << std::endl; } void baz(void) { x = 5; } int x; }; int main(void) { foo* f = 0; f->bar(); // (a) f->baz(); // (b) } We expect (b) to crash, because there is no corresponding member x for the null pointer. In practice, (a) doesn't crash because the this pointer is never used. Because (b) dereferences the this pointer (this->x = 5;), and this is null, the program enters undefined behavior. Does (a) result in undefined behavior? What about if both functions are static?

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  • What is the proper way to URL encode Unicode characters?

    - by Josh Gibson
    I know of the non-standard %uxxxx scheme but that doesn't seem like a wise choice since the scheme has been rejected by the W3C. Some interesting examples: The heart character. If I type this into my browser: http://www.google.com/search?q=? Then copy and paste it, I see this URL http://www.google.com/search?q=%E2%99%A5 which makes it seem like Firefox (or Safari) is doing this. urllib.quote_plus(x.encode("latin-1")) '%E2%99%A5' which makes sense, except for things that can't be encoded in Latin-1, like the triple dot character. … If I type the URL http://www.google.com/search?q=… into my browser then copy and paste, I get http://www.google.com/search?q=%E2%80%A6 back. Which seems to be the result of doing urllib.quote_plus(x.encode("utf-8")) which makes sense since … can't be encoded with Latin-1. But then its not clear to me how the browser knows whether to decode with UTF-8 or Latin-1. Since this seems to be ambiguous: In [67]: u"…".encode('utf-8').decode('latin-1') Out[67]: u'\xc3\xa2\xc2\x80\xc2\xa6' works, so I don't know how the browser figures out whether to decode that with UTF-8 or Latin-1. What's the right thing to be doing with the special characters I need to deal with?

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  • Global qualification in a class declarations class-head

    - by gf
    We found something similar to the following (don't ask ...): namespace N { struct A { struct B; }; } struct A { struct B; }; using namespace N; struct ::A::B {}; // <- point of interest Interestingly, this compiles fine with VS2005, icc 11.1 and Comeau (online), but fails with GCC: global qualification of class name is invalid before '{' token From C++03, Annex A, it seems to me like GCC is right: the class-head can consist of nested-name-specifier and identifier nested-name-specifier can't begin with a global qualification (::) obviously, neither can identifier ... or am i overlooking something?

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  • Why does std::cout convert volatile pointers to bool?

    - by Joseph Garvin
    If you try to cout a volatile pointer, even a volatile char pointer where you would normally expect cout to print the string, you will instead simply get '1' (assuming the pointer is not null I think). I assume output stream operator<< is template specialized for volatile pointers, but my question is, why? What use case motivates this behavior? Example code: #include <iostream> #include <cstring> int main() { char x[500]; std::strcpy(x, "Hello world"); int y; int *z = &y; std::cout << x << std::endl; std::cout << (char volatile*)x << std::endl; std::cout << z << std::endl; std::cout << (int volatile*)z << std::endl; return 0; } Output: Hello world 1 0x8046b6c 1

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  • ActiveMQ AJax Client

    - by Lily
    I try to write a simple Ajax client to send and receive messages. It's successfully deployed but I have never received msg from the client. I am beating myself to think out what I am missing, but still can't make it work. Here is my code: I creat a dynamic web application named: ActiveMQAjaxService and put activemq-web.jar and all neccessary dependencies in the WEB-INF/lib folder. In this way, AjaxServlet and MessageServlet will be deployed I start activemq server in command line: ./activemq = activemq successfully created and display: Listening for connections at: tcp://lilyubuntu:61616 INFO | Connector openwire Started INFO | ActiveMQ JMS Message Broker (localhost, ID:lilyubuntu-56855-1272317001405-0:0) started INFO | Logging to org.slf4j.impl.JCLLoggerAdapter(org.mortbay.log) via org.mortbay.log.Slf4jLog INFO | jetty-6.1.9 INFO | ActiveMQ WebConsole initialized. INFO | Initializing Spring FrameworkServlet 'dispatcher' INFO | ActiveMQ Console at http://0.0.0.0:8161/admin INFO | Initializing Spring root WebApplicationContext INFO | Connector vm://localhost Started INFO | Camel Console at http://0.0.0.0:8161/camel INFO | ActiveMQ Web Demos at http://0.0.0.0:8161/demo INFO | RESTful file access application at http://0.0.0.0:8161/fileserver INFO | Started [email protected]:8161 3) index.xml, which is the html to test the client: <?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <script type="text/javascript" src="amq/amq.js"></script> <script type="text/javascript">amq.uri='amq';</script> <title>Hello Ajax ActiveMQ</title> </head> <body> <p>Hello World!</p> <script type="text/javascript"> amq.sendMessage("topic://myDetector", "message"); var myHandler = { rcvMessage: function(message) { alert("received "+message); } }; function myPoll(first) { if (first) { amq.addListener('myDetector', 'topic://myDetector', myHandler.rcvMessage); } } amq.addPollHandler(myPoll); 4) Web.xml: ActiveMQ Web Demos Apache ActiveMQ Web Demos org.apache.activemq.brokerURL vm://localhost (I also tried tcp://localhost:61616) The URL of the Message Broker to connect to org.apache.activemq.embeddedBroker true Whether we should include an embedded broker or not <!-- the subscription REST servlet --> <servlet> <servlet-name>AjaxServlet</servlet-name> <servlet-class>org.apache.activemq.web.AjaxServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet> <servlet-name>MessageServlet</servlet-name> <servlet-class>org.apache.activemq.web.MessageServlet</servlet-class> <load-on-startup>1</load-on-startup> <!-- Uncomment this parameter if you plan to use multiple consumers over REST <init-param> <param-name>destinationOptions</param-name> <param-value>consumer.prefetchSize=1</param-value> </init-param> --> </servlet> <!-- the queue browse servlet --> <filter> <filter-name>session</filter-name> <filter-class>org.apache.activemq.web.SessionFilter</filter-class> </filter> <filter-mapping> <filter-name>session</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> After all of these, I deploy the web-app, and it's successfully deployed, but when I try it out in http://localhost:8080/ActiveMQAjaxService/index.html , nothing happens. I can run the demo portfolioPublisher demo successfully at http://localhost:8161/demo/portfolio/portfolio.html, and see the numbers updated all the time. But for my simple web-app, nothing really works. Any suggestion/hint is welcomed. Thanks so much Lily

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  • Why would you use "AS" when aliasing a SQL table?

    - by froadie
    I just came across a SQL statement that uses AS to alias tables, like this: SELECT all, my, stuff FROM someTableName AS a INNER JOIN someOtherTableName AS b ON a.id = b.id What I'm used to seeing is: SELECT all, my, stuff FROM someTableName a INNER JOIN someOtherTableName b ON a.id = b.id I'm assuming there's no difference and it's just syntactic sugar, but which of these is more prevalent/wide-spread? Is there any reason to prefer one over the other?

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  • Why is it assumed that send may return with less than requested data transmitted on a blocking socke

    - by Ernelli
    The standard method to send data on a stream socket has always been to call send with a chunk of data to write, check the return value to see if all data was sent and then keep calling send again until the whole message has been accepted. For example this is a simple example of a common scheme: int send_all(int sock, unsigned char *buffer, int len) { int nsent; while(len 0) { nsent = send(sock, buffer, len, 0); if(nsent == -1) // error return -1; buffer += nsent; len -= nsent; } return 0; // ok, all data sent } Even the BSD manpage mentions that ...If no messages space is available at the socket to hold the message to be transmitted, then send() normally blocks... Which indicates that we should assume that send may return without sending all data. Now I find this rather broken but even W. Richard Stevens assumes this in his standard reference book about network programming, not in the beginning chapters, but the more advanced examples uses his own writen (write all data) function instead of calling write. Now I consider this still to be more or less broken, since if send is not able to transmit all data or accept the data in the underlying buffer and the socket is blocking, then send should block and return when the whole send request has been accepted. I mean, in the code example above, what will happen if send returns with less data sent is that it will be called right again with a new request. What has changed since last call? At max a few hundred CPU cycles have passed so the buffer is still full. If send now accepts the data why could'nt it accept it before? Otherwise we will end upp with an inefficient loop where we are trying to send data on a socket that cannot accept data and keep trying, or else? So it seems like the workaround, if needed, results in heavily inefficient code and in those circumstances blocking sockets should be avoided at all an non blocking sockets together with select should be used instead.

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  • Can a destructor be recursive?

    - by Cubbi
    Is this program well-defined, and if not, why exactly? #include <iostream> #include <new> struct X { int cnt; X (int i) : cnt(i) {} ~X() { std::cout << "destructor called, cnt=" << cnt << std::endl; if ( cnt-- > 0 ) this->X::~X(); // explicit recursive call to dtor } }; int main() { char* buf = new char[sizeof(X)]; X* p = new(buf) X(7); p->X::~X(); // explicit call to dtor delete[] buf; } My reasoning: although invoking a destructor twice is undefined behavior, per 12.4/14, what it says exactly is this: the behavior is undefined if the destructor is invoked for an object whose lifetime has ended Which does not seem to prohibit recursive calls. While the destructor for an object is executing, the object's lifetime has not yet ended, thus it's not UB to invoke the destructor again. On the other hand, 12.4/6 says: After executing the body [...] a destructor for class X calls the destructors for X's direct members, the destructors for X's direct base classes [...] which means that after the return from a recursive invocation of a destructor, all member and base class destructors will have been called, and calling them again when returning to the previous level of recursion would be UB. Therefore, a class with no base and only POD members can have a recursive destructor without UB. Am I right?

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  • When is a C++ terminate handler the Right Thing(TM)?

    - by Joseph Garvin
    The C++ standard provides the std::set_terminate function which lets you specify what function std::terminate should actually call. std::terminate should only get called in dire circumstances, and sure enough the situations the standard describes for when it's called are dire (e.g. an uncaught exception). When std::terminate does get called the situation seems analagous to being out of memory -- there's not really much you can sensically do. I've read that it can be used to make sure resources are freed -- but for the majority of resources this should be handled automatically by the OS when the process exits (e.g. file handles). Theoretically I can see a case for if say, you needed to send a server a specific message when exiting due to a crash. But the majority of the time the OS handling should be sufficient. When is using a terminate handler the Right Thing(TM)? Update: People interested in what can be done with custom terminate handlers might find this non-portable trick useful.

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  • How does the last integer promotion rule ever get applied in C?

    - by SiegeX
    6.3.1.8p1: Otherwise, the integer promotions are performed on both operands. Then the following rules are applied to the promoted operands: If both operands have the same type, then no further conversion is needed. Otherwise, if both operands have signed integer types or both have unsigned integer types, the operand with the type of lesser integer conversion rank is converted to the type of the operand with greater rank. Otherwise, if the operand that has unsigned integer type has rank greater or equal to the rank of the type of the other operand, then the operand with signed integer type is converted to the type of the operand with unsigned integer type. Otherwise, if the type of the operand with signed integer type can represent all of the values of the type of the operand with unsigned integer type, then the operand with unsigned integer type is converted to the type of the operand with signed integer type. Otherwise, both operands are converted to the unsigned integer type corresponding to the type of the operand with signed integer type. For the bolded rule to be applied it would seem to imply you need to have have an unsigned interger type who's rank is less than the signed integer type and the signed integer type cannot hold all the values of the unsigned integer type. Is there a real world example of such a case or is this statement serving as a catch-all to cover all possible permutations?

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  • How do you do A/B switching in a web app? (for deploying updates)

    - by stagas
    I currently have a mysite.com (A) which points to /public_html/ and a dev.mysite.com (B) which I created a /dev_html/ for that. I cloned the site but now I need a way of switching between them without having to copy all the files from one dir to another and without bringing the site down. I just want to switch the live site to B and then work on A, and when I finish, switch the live site to A and work on B. Is there a simple way? I'm using cPanel X and cPanel 11 (WHM VPS). Also, both can interact with the same database so that's not an issue as I'm not changing any database structure. Only the php/js/img files need to switch.

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  • Can a conforming C implementation #define NULL to be something wacky

    - by janks
    I'm asking because of the discussion that's been provoked in this thread: http://stackoverflow.com/questions/2597142/when-was-the-null-macro-not-0/2597232 Trying to have a serious back-and-forth discussion using comments under other people's replies is not easy or fun. So I'd like to hear what our C experts think without being restricted to 500 characters at a time. The C standard has precious few words to say about NULL and null pointer constants. There's only two relevant sections that I can find. First: 3.2.2.3 Pointers An integral constant expression with the value 0, or such an expression cast to type void * , is called a null pointer constant. If a null pointer constant is assigned to or compared for equality to a pointer, the constant is converted to a pointer of that type. Such a pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function. and second: 4.1.5 Common definitions <stddef.h> The macros are NULL which expands to an implementation-defined null pointer constant; The question is, can NULL expand to an implementation-defined null pointer constant that is different from the ones enumerated in 3.2.2.3? In particular, could it be defined as: #define NULL __builtin_magic_null_pointer Or even: #define NULL ((void*)-1) My reading of 3.2.2.3 is that it specifies that an integral constant expression of 0, and an integral constant expression of 0 cast to type void* must be among the forms of null pointer constant that the implementation recognizes, but that it isn't meant to be an exhaustive list. I believe that the implementation is free to recognize other source constructs as null pointer constants, so long as no other rules are broken. So for example, it is provable that #define NULL (-1) is not a legal definition, because in if (NULL) do_stuff(); do_stuff() must not be called, whereas with if (-1) do_stuff(); do_stuff() must be called; since they are equivalent, this cannot be a legal definition of NULL. But the standard says that integer-to-pointer conversions (and vice-versa) are implementation-defined, therefore it could define the conversion of -1 to a pointer as a conversion that produces a null pointer. In which case if ((void*)-1) would evaluate to false, and all would be well. So what do other people think? I'd ask for everybody to especially keep in mind the "as-if" rule described in 2.1.2.3 Program execution. It's huge and somewhat roundabout, so I won't paste it here, but it essentially says that an implementation merely has to produce the same observable side-effects as are required of the abstract machine described by the standard. It says that any optimizations, transformations, or whatever else the compiler wants to do to your program are perfectly legal so long as the observable side-effects of the program aren't changed by them. So if you are looking to prove that a particular definition of NULL cannot be legal, you'll need to come up with a program that can prove it. Either one like mine that blatantly breaks other clauses in the standard, or one that can legally detect whatever magic the compiler has to do to make the strange NULL definition work. Steve Jessop found an example of way for a program to detect that NULL isn't defined to be one of the two forms of null pointer constants in 3.2.2.3, which is to stringize the constant: #define stringize_helper(x) #x #define stringize(x) stringize_helper(x) Using this macro, one could puts(stringize(NULL)); and "detect" that NULL does not expand to one of the forms in 3.2.2.3. Is that enough to render other definitions illegal? I just don't know. Thanks!

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  • How to build a web site which gives a sub-domain dynamically to every registered user?

    - by coderex
    Suppose i have a site and i wish to give a sub-domain for each registered users. like my site http://site.com/ and the test-user is a user registered on my site and site want to make sub-domain for that user. Like http://test-user.site.com Like http://test-user1.site.com for test-user1. Hop you understood the requirement. How can i create a sub-domain using my sites back-end. or dynamically while register

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