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• Warning: cast increases required alignment

  - by dash-tom-bang

  I'm recently working on this platform for which a legacy codebase issues a large number of "cast increases required alignment to N" warnings, where N is the size of the target of the cast. struct Message { int32_t id; int32_t type; int8_t data[16]; }; int32_t GetMessageInt(const Message& m) { return *reinterpret_cast<int32_t*>(&data[0]); } Hopefully it's obvious that a "real" implementation would be a bit more complex, but the basic point is that I've got data coming from somewhere, I know that it's aligned (because I need the id and type to be aligned), and yet I get the message that the cast is increasing the alignment, in the example case, to 4. Now I know that I can suppress the warning with an argument to the compiler, and I know that I can cast the bit inside the parentheses to void* first, but I don't really want to go through every bit of code that needs this sort of manipulation (there's a lot because we load a lot of data off of disk, and that data comes in as char buffers so that we can easily pointer-advance), but can anyone give me any other thoughts on this problem? I mean, to me it seems like such an important and common option that you wouldn't want to warn, and if there is actually the possibility of doing it wrong then suppressing the warning isn't going to help. Finally, can't the compiler know as I do how the object in question is actually aligned in the structure, so it should be able to not worry about the alignment on that particular object unless it got bumped a byte or two?

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• c++ File input/output

  - by Myx

  Hi: I am trying to read from a file using fgets and sscanf. In my file, I have characters on each line of the while which I wish to put into a vector. So far, I have the following: FILE *fp; fp = fopen(filename, "r"); if(!fp) { fprintf(stderr, "Unable to open file %s\n", filename); return 0; } // Read file int line_count = 0; char buffer[1024]; while(fgets(buffer, 1023, fp)) { // Increment line counter line_count++; char *bufferp = buffer; ... while(*bufferp != '\n') { char *tmp; if(sscanf(bufferp, "%c", tmp) != 1) { fprintf(stderr, "Syntax error reading axiom on " "line %d in file %s\n", line_count, filename); return 0; } axiom.push_back(tmp); printf("put %s in axiom vector\n", axiom[axiom.size()-1]); // increment buffer pointer bufferp++; } } my axiom vector is defined as vector<char *> axiom;. When I run my program, I get a seg fault. It happens when I do the sscanf. Any suggestions on what I'm doing wrong?

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• JQuery drag, drop and save via cookie - how to?

  - by RussP

  Sorry to be back folks, but you guys & girls seem to know much more about this than I do ... anyhow, here is my question/problem I want to use drag, drop, sort (the interface plugin does me even though I have read it's out of date? but have looked at UI and to be honest is not clear and to me appears heavier than interface?) Anyhow, how do I set a cookie to save positions from this: $(document).ready( function () { $('a.closeEl').bind('click', toggleContent); $('div.groupWrapper').Sortable( { accept: 'groupItem', helperclass: 'sortHelper', activeclass : 'sortableactive', hoverclass : 'sortablehover', handle: 'div.itemHeader', tolerance: 'pointer', onChange : function(ser) { }, onStart : function() { $.iAutoscroller.start(this, document.getElementsByTagName('body')); }, onStop : function() { $.iAutoscroller.stop(); } } ); } ); var toggleContent = function(e) { var targetContent = $('div.itemContent', this.parentNode.parentNode); if (targetContent.css('display') == 'none') { targetContent.slideDown(300); $(this).html('[-]'); } else { targetContent.slideUp(300); $(this).html('[+]'); } return false; }; var ser = function (s) { serial = $.SortSerialize(s); alert(serial.hash); }; which is the "standard" interface demo, PLUS How do I then get to read that cookie so that when I next visit the page the order is as I set it in the cookie? Hopefully from that I can work out the rest .......? Thanks for help in advance.

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• Who's setting TCP window size down to 0, Indy or Windows?

  - by François

  We have an application server which have been observed sending headers with TCP window size 0 at times when the network had congestion (at a client's site). We would like to know if it is Indy or the underlying Windows layer that is responsible for adjusting the TCP window size down from the nominal 64K in adaptation to the available throughput. And we would be able to act upon it becoming 0 (nothing gets send, users wait = no good). So, any info, link, pointer to Indy code are welcome... Disclaimer: I'm not a network specialist. Please keep the answer understandable for the average me ;-) Note: it's Indy9/D2007 on Windows Server 2003 SP2. More gory details: The TCP zero window cases happen on the middle tier talking to the DB server. It happens at the same moments when end users complain of slowdowns in the client application (that's what triggered the network investigation). 2 major Network issues causing bottlenecks have been identified. The TCP zero window happened when there was network congestion, but may or may not be caused by it. We want to know when that happen and have a way to do something (logging at least) in our code. So where to hook (in Indy?) to know when that condition occurs?

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• OSMF seek with Amazon Cloudfront

  - by giorrrgio

  I've written a little OSMF player that streams via RTMP from Amazon Cloudfront. There's a known issue, the mp3 duration is not correctly readed from metadata and thus the seek function is not working. I know there's a workaround implying the use of getStreamLength function of NetConnection, which I successfully implemented in a previous non-OSMF player, but now I don't know how and when to call it, in terms of OSMF Events and Traits. This code is not working: protected function initApp():void { //the pointer to the media var resource:URLResource = new URLResource( STREAMING_PATH ); // Create a mediafactory instance mediaFactory = new DefaultMediaFactory(); //creates and sets the MediaElement (generic) with a resource and path element = mediaFactory.createMediaElement( resource ); var loadTrait:NetStreamLoadTrait = element.getTrait(MediaTraitType.LOAD) as NetStreamLoadTrait; loadTrait.addEventListener(LoaderEvent.LOAD_STATE_CHANGE, _onLoaded); player = new MediaPlayer( element ); //Marker 5: Add MediaPlayer listeners for media size and current time change player.addEventListener( DisplayObjectEvent.MEDIA_SIZE_CHANGE, _onSizeChange ); player.addEventListener( TimeEvent.CURRENT_TIME_CHANGE, _onProgress ); initControlBar(); } private function onGetStreamLength(result:Object):void { Alert.show("The stream length is " + result + " seconds"); duration = Number(result); } private function _onLoaded(e:LoaderEvent):void { if (e.newState == LoadState.READY) { var loadTrait:NetStreamLoadTrait = player.media.getTrait(MediaTraitType.LOAD) as NetStreamLoadTrait; if (loadTrait && loadTrait.netStream) { var responder:Responder = new Responder(onGetStreamLength); loadTrait.connection.call("getStreamLength", responder, STREAMING_PATH); } } }

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• Question about Virtual Inheritance hierarchy

  - by Summer_More_More_Tea

  Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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• How can I modified the value of a string defined in a struc?

  - by Eric

  Hi, I have the following code in c++: define TAM 4000 define NUMPAGS 512 struct pagina { bitset<12 direccion; char operacion; char permiso; string *dato; int numero; }; void crearPagina(pagina* pag[], int pos, int dir) { pagina * paginas = (pagina*)malloc(sizeof(char) * TAM); paginas - direccion = bitset<12 (dir); paginas - operacion = 'n'; paginas - permiso = 'n'; string **tempDato = &paginas - dato; char *temp = " "; **tempDato = temp; paginas - numero = 0; pag[pos] = paginas; } I want to modify the value of the variable called "string *dato" in the struct pagina but, everytime I want to assing a new value, the compiler throws a segmentation fault. In this case I'm using a pointer to string, but I have also tried with a string. In a few words I want to do the following: pagina - dato = "test"; Any idea? Thanks in advance!!!

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• Implementing list position locator in C++?

  - by jfrazier

  I am writing a basic Graph API in C++ (I know libraries already exist, but I am doing it for the practice/experience). The structure is basically that of an adjacency list representation. So there are Vertex objects and Edge objects, and the Graph class contains: list<Vertex *> vertexList list<Edge *> edgeList Each Edge object has two Vertex* members representing its endpoints, and each Vertex object has a list of Edge* members representing the edges incident to the Vertex. All this is quite standard, but here is my problem. I want to be able to implement deletion of Edges and Vertices in constant time, so for example each Vertex object should have a Locator member that points to the position of its Vertex* in the vertexList. The way I first implemented this was by saving a list::iterator, as follows: vertexList.push_back(v); v->locator = --vertexList.end(); Then if I need to delete this vertex later, then rather than searching the whole vertexList for its pointer, I can call: vertexList.erase(v->locator); This works fine at first, but it seems that if enough changes (deletions) are made to the list, the iterators will become out-of-date and I get all sorts of iterator errors at runtime. This seems strange for a linked list, because it doesn't seem like you should ever need to re-allocate the remaining members of the list after deletions, but maybe the STL does this to optimize by keeping memory somewhat contiguous? In any case, I would appreciate it if anyone has any insight as to why this happens. Is there a standard way in C++ to implement a locator that will keep track of an element's position in a list without becoming obsolete? Much thanks, Jeff

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• Invoking a function (main()) from a binary file in C

  - by Dhara Darji

  I have simple c program like, my_bin.c: #include <stdio.h> int main() { printf("Success!\n"); return 0; } I compile it with gcc and got executable: my_bin. Now I want to invoke main (or run this my_bin) using another C program. That I did with mmap and function pointer like this: #include <stdio.h> #include <fcntl.h> #include <sys/mman.h> int main() { void (*fun)(); int fd; int *map; fd = open("./my_bin", O_RDONLY); map = mmap(0, 8378, PROT_READ, MAP_SHARED, fd, 0); fun = map; fun(); return 0; } PS: I went through some tutorial, for how to read binary file and execute. But this gives Seg fault, any help appreciated! Thanks!

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• Do ORMs normally allow circular relations? If so, how would they handle it?

  - by SeanJA

  I was hacking around trying to make a basic orm that has support for the one => one and one => many relationships. I think I succeeded somewhat, but I am curious about how to handle circular relationships. Say you had something like this: user::hasOne('car'); car::hasMany('wheels'); car::property('type'); wheel::hasOne('car'); You could then do this (theoretically): $u = new user(); echo $u->car->wheels[0]->car->wheels[1]->car->wheels[2]->car->wheels[3]->type; #=> "monster truck" Now, I am not sure why you would want to do this. It seems like it wastes a whole pile of memory and time just to get to something that could have been done in a much shorter way. In my small ORM, I now have 4 copies of the wheel class, and 4 copies of the car class in memory, which causes a problem if I update one of them and save it back to the database, the rest get out of date, and could overwrite the changes that were already made. How do other ORMs handle circular references? Do they even allow it? Do they go back up the tree and create a pointer to one of the parents? DO they let the coder shoot themselves in the foot if they are silly enough to go around in circles?

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• How to partition bits in a bit array with less than linear time

  - by SiLent SoNG

  This is an interview question I faced recently. Given an array of 1 and 0, find a way to partition the bits in place so that 0's are grouped together, and 1's are grouped together. It does not matter whether 1's are ahead of 0's or 0's are ahead of 1's. An example input is 101010101, and output is either 111110000 or 000011111. Solve the problem in less than linear time. Make the problem simpler. The input is an integer array, with each element either 1 or 0. Output is the same integer array with integers partitioned well. To me, this is an easy question if it can be solved in O(N). My approach is to use two pointers, starting from both ends of the array. Increases and decreases each pointer; if it does not point to the correct integer, swap the two. int * start = array; int * end = array + length - 1; while (start < end) { // Assume 0 always at the end if (*end == 0) { --end; continue; } // Assume 1 always at the beginning if (*start == 1) { ++start; continue; } swap(*start, *end); } However, the interview insists there is a sub-linear solution. This makes me thinking hard but still not get an answer. Can anyone help on this interview question?

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• How can I get type information at runtime from a DMP file in a Windbg extension?

  - by pj4533

  This is related to my previous question, regarding pulling objects from a dmp file. As I mentioned in the previous question, I can successfully pull object out of the dmp file by creating wrapper 'remote' objects. I have implemented several of these so far, and it seems to be working well. However I have run into a snag. In one case, a pointer is stored in a class, say of type 'SomeBaseClass', but that object is actually of the type 'SomeDerivedClass' which derives from 'SomeBaseClass'. For example it would be something like this: MyApplication!SomeObject +0x000 field1 : Ptr32 SomeBaseClass +0x004 field2 : Ptr32 SomeOtherClass +0x008 field3 : Ptr32 SomeOtherClass I need someway to find out what the ACTUAL type of 'field1' is. To be more specific, using example addresses: MyApplication!SomeObject +0x000 field1 : 0cae2e24 SomeBaseClass +0x004 field2 : 0x262c8d3c SomeOtherClass +0x008 field3 : 0x262c8d3c SomeOtherClass 0:000> dt SomeBaseClass 0cae2e24 MyApplication!SomeBaseClass +0x000 __VFN_table : 0x02de89e4 +0x038 basefield1 : (null) +0x03c basefield2 : 3 0:000> dt SomeDerivedClass 0cae2e24 MyApplication!SomeDerivedClass +0x000 __VFN_table : 0x02de89e4 +0x038 basefield1 : (null) +0x03c basefield2 : 3 +0x040 derivedfield1 : 357 +0x044 derivedfield2 : timecode_t When I am in WinDbg, I can do this: dt 0x02de89e4 And it will show the type: 0:000> dt 0x02de89e4 SomeDerivedClass::`vftable' Symbol not found. But how do get that inside an extension? Can I use SearchMemory() to look for 'SomeDerivedClass::`vftable'? If you follow my other question, I need this type information so I know what type of wrapper remote classes to create. I figure it might end up being some sort of case-statement, where I have to match a string to a type? I am ok with that, but I still don't know where I can get that string that represents the type of the object in question (ie SomeObject-field1 in the above example).

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• Can some tell me why I am seg faulting in this simple C program?

  - by user299648

  I keep on getting seg faulted after I end my first for loop, and for the life of me I don't why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I don't know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( 15*sizeof(char) ); char** picks = malloc(15*sizeof(char*)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { scanf( "%s", picks+num_picks ); } //this is where i seg fault int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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• Can someone tell me why I'm seg faulting in this simple C program?

  - by user299648

  I keep on getting seg faulted, and for the life of me I dont why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I dont know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( sizeof(char) ); char** picks = malloc(15*sizeof(char)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { printf("pick a/an %s ", string ); scanf( "%s", picks+num_picks ); } int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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• How do I build a filtered_streambuf based on basic_streambuf?

  - by swestrup

  I have a project that requires me to insert a filter into a stream so that outgoing data will be modified according to the filter. After some research, it seems that what I want to do is create a filtered_streambuf like this: template <class StreamBuf class filtered_streambuf: public StreamBuf { ... } And then insert a filtered_streambuf<> into whichever stream I need to be filtered. My problem is that I don't know what invariants I need to maintain while filtering a stream, in order to ensure that Derived classes can work as expected. In particular, I may find I have filtered_streambufs built over other filtered_streambufs. All the various stream inserters, extractors and manipulators work as expected. The trouble is that I just can't seem to work out what the minimal interface is that I need to supply in order to guarantee that an iostream will have what it needs to work correctly. In particular, do I need to fake the movement of the protected pointer variables, or not? Do I need a fake data buffer, or not? Can I just override the public functions, rewriting them in terms of the base streambuf, or is that too simplistic?

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• How is external memory, internal memory, and cache organized?

  - by goldenmean

  Consider a system as follows:= A hardware board having say ARM Cortex-A8 and Neon Vector coprocessor, and Embedded Linux OS running on Cortex-A8. On this environment, if there is some application - say, a video decoder is executing - then: How is it decided that which buffers would be in external memory, which ones would be allocated in internal SRAM, etc. When one says calloc/malloc on such system/code, the pointer returned is from which memory: internal or external? Can a user make buffers to be allocated to the memories of his choice (internal/external)? In ARM architectures, there is another memory called as Tightly coupled memory (TCM). What is that and how can user enable and use it? Can I declare buffers in this memory? Do I need to see the memory map (if any) of the hardware board to understand about all these different physical memories present in a typical hardware board? How much of a role does the OS play in distinguishing these different memories? Sorry for multiple questions, but i think they all are interlinked.

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• Static Vs Non-Static Method Performance C#

  - by dotnetguts

  Hello All, I have few global methods declared in public class in my asp.net web application. I have habbit of declaring all global methods in public class in following format public static string MethodName(parameters) { } I want to know how it would impact on performance point of view? 1) Which one is Better? Static Method or Non-Static Method? 2) Reason why it is better? Following link shows Non-Static methods are good because, static methods are using locks to be Thread-safe. The always do internally a Monitor.Enter() and Monitor.exit() to ensure Thread-safety. http://bytes.com/topic/c-sharp/answers/231701-static-vs-non-static-function-performance And Following link shows Static Methods are good static methods are normally faster to invoke on the call stack than instance methods. There are several reasons for this in the C# programming language. Instance methods actually use the 'this' instance pointer as the first parameter, so an instance method will always have that overhead. Instance methods are also implemented with the callvirt instruction in the intermediate language, which imposes a slight overhead. Please note that changing your methods to static methods is unlikely to help much on ambitious performance goals, but it can help a tiny bit and possibly lead to further reductions. http://dotnetperls.com/static-method I am little confuse which one to use? Thanks

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• Write to memory buffer instead of file with libjpeg?

  - by Richard Knop

  I have found this function which uses libjpeg to write to a file: int write_jpeg_file( char *filename ) { struct jpeg_compress_struct cinfo; struct jpeg_error_mgr jerr; /* this is a pointer to one row of image data */ JSAMPROW row_pointer[1]; FILE *outfile = fopen( filename, "wb" ); if ( !outfile ) { printf("Error opening output jpeg file %s\n!", filename ); return -1; } cinfo.err = jpeg_std_error( &jerr ); jpeg_create_compress(&cinfo); jpeg_stdio_dest(&cinfo, outfile); /* Setting the parameters of the output file here */ cinfo.image_width = width; cinfo.image_height = height; cinfo.input_components = bytes_per_pixel; cinfo.in_color_space = color_space; /* default compression parameters, we shouldn't be worried about these */ jpeg_set_defaults( &cinfo ); /* Now do the compression .. */ jpeg_start_compress( &cinfo, TRUE ); /* like reading a file, this time write one row at a time */ while( cinfo.next_scanline < cinfo.image_height ) { row_pointer[0] = &raw_image[ cinfo.next_scanline * cinfo.image_width * cinfo.input_components]; jpeg_write_scanlines( &cinfo, row_pointer, 1 ); } /* similar to read file, clean up after we're done compressing */ jpeg_finish_compress( &cinfo ); jpeg_destroy_compress( &cinfo ); fclose( outfile ); /* success code is 1! */ return 1; } I would actually need to write the jpeg compressed image just to memory buffer, without saving it to a file, to save time. Could somebody give me an example how to do it? I have been searching the web for a while but the documentation is very rare if any and examples are also difficult to come by.

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• Java abstract visitor - guarantueed to succeed? If so, why?

  - by disown

  I was dealing with hibernate, trying to figure out the run-time class behind proxied instances by using the visitor pattern. I then came up with an AbstractVisitable approach, but I wonder if it will always produce correct results. Consider the following code: interface Visitable { public void accept(Visitor v); } interface Visitor { public void visit(Visitable visitorHost); } abstract class AbstractVisitable implements Visitable { @Override public void accept(Visitor v) { v.visit(this); } } class ConcreteVisitable extends AbstractVisitable { public static void main(String[] args) { final Visitable visitable = new ConcreteVisitable(); final Visitable proxyVisitable = (Visitable) Proxy.newProxyInstance( Thread.currentThread().getContextClassLoader(), new Class<?>[] { Visitable.class }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(visitable, args); } }); proxyVisitable.accept(new Visitor() { @Override public void visit(Visitable visitorHost) { System.out.println(visitorHost.getClass()); } }); } } This makes a ConcreteVisitable which inherits the accept method from AbstractVisitable. In c++, I would consider this risky, since this in AbstractVisitable could be referencing to AbstractVisitable::this, and not ConcreteVisitable::this. I was worried that the code under certain circumstances would print class AbstractVisible. Yet the code above outputs class ConcreteVisitable, even though I hid the real type behind a dynamic proxy (the most difficult case I could come up with). Is the abstract visitor approach above guaranteed to work, or are there some pitfalls with this approach? What guarantees are given in Java with respect to the this pointer?

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• error in C++, what to do ?: could not find an match for ostream::write(long *, unsigned int)

  - by Shantanu Gupta

  I am trying to write data stored in a binary file using turbo C++. But it shows me an error could not find an match for ostream::write(long *, unsigned int) I want to write a 4 byte long data into that file. When i tries to write data using char pointer. It runs successfully. But i want to store large value i.e. eg. 2454545454 Which can be stored in long only. I dont know how to convert 1 byte into bit. I have 1 byte of data as a character. Moreover what i m trying to do is to convert 4 chars into long and store data into it. And at the other side i want to reverse this so as to retrieve how many bytes of data i have written. long *lmem; lmem=new long; *lmem=Tsize; fo.write(lmem,sizeof(long));// error occurs here delete lmem; I am implementing steganography and i have successfully stored txt file into image but trying to retrieve that file data now.

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• How to get address of va_arg?

  - by lionbest

  I hack some old C API and i got a compile error with the following code: void OP_Exec( OP* op , ... ) { int i; va_list vl; va_start(vl,op); for( i = 0; i < op->param_count; ++i ) { switch( op->param_type[i] ) { case OP_PCHAR: op->param_buffer[i] = va_arg(vl,char*); // ok it works break; case OP_INT: op->param_buffer[i] = &va_arg(vl,int); // error here break; // ... more here } } op->pexec(op); va_end(vl); } The error with gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu9) was: main.c|55|error: lvalue required as unary ‘&’ operand So why exactly it's not possible here to get a pointer to argument? How to fix it? This code is executed very often with different OP*, so i prefer to not allocate extra memory. Is it possible to iterate over va_list knowing only the size of arguments?

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• Jquery drag /drop and clone

  - by Sajeev

  Hi I need to achive this .. I have a set of droppable items ( basically I am droping designs on a apparel ) and I am dropping a clone.. If I don't like the dropped object (designs) - I want to delete that by doing something like hidden . But I am unable to do that. Please help me.. here is the code var clone; $(document).ready(function(){ $(".items").draggable({helper: 'clone',cursor: 'hand'}); $(".droparea").droppable({ accept: ".items", hoverClass: 'dropareahover', tolerance: 'pointer', drop: function(ev, ui) { var dropElemId = ui.draggable.attr("id"); var dropElem = ui.draggable.html(); clone = $(dropElem).clone(); // clone it and hold onto the jquery object clone.id="newId"; clone.css("position", "absolute"); clone.css("top", ui.absolutePosition.top); clone.css("left", ui.absolutePosition.left); clone.draggable({ containment: 'parent' ,cursor: 'crosshair'}); $(this).append(clone); alert("done dragging "); /lets assume I have a delete button when I click that clone should dissapear so that I can drop another design - but the following code has no effect //and the item is still visible , how to make it dissapear ? $('#newId').css("visibility","hidden"); } }); });

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• Multi-reader IPC solution?

  - by gct

  I'm working on a framework in C++ (just for fun for now), that lets the user write plugins that use a standard API to stream data between each other. There's going to be three basic transport mechanisms for the data: files, sockets, and some kind of IPC piping system. The system is set up so that for the non-file transport, each stream can have multiple readers. IE once a server socket it setup, multiple computers can connect and stream the data. I'm a little stuck at the multi-reader IPC system though. All my plugins run in threads so they live in the same address space, so some kind of shared memory system would work fine, I was thinking I'd write my own circular buffer with a write pointer and read pointers chassing it around the buffer, but I have my doubts that I can achieve the same performance as something like linux pipes. I'm curious what people would suggest for a multi-reader solution to something like this? Is the overhead for pipes or domain sockets low enough that I could just open a connection to each reader and issue separate writes to each reader? This is intended to be significant volumes of data (tens of mega-samples/sec), so performance is a must.

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• How to pass data to a C++0x lambda function that will run in a different thread?

  - by Dimitri C.

  In our company we've written a library function to call a function asynchronously in a separate thread. It works using a combination of inheritance and template magic. The client code looks as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, &DemoThread::SomeFunction, stringToPassByValue); Since the introduction of lambda functions I'd like to use it in combination with lambda functions. I'd like to write the following client code: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=]() { const std::string someCopy = stringToPassByValue; }); Now, with the Visual C++ 2010 this code doesn't work. What happens is that the stringToPassByValue is not copied. Instead the "capture by value" feature passes the data by reference. The result is that if the function is executed after stringToPassByValue has gone out of scope, the application crashes as its destructor is called already. So I wonder: is it possible to pass data to a lambda function as a copy? Note: One possible solution would be to modify our framework to pass the data in the lambda parameter declaration list, as follows: DemoThread thread; std::string stringToPassByValue = "The string to pass by value"; AsyncCall(thread, [=](const std::string stringPassedByValue) { const std::string someCopy = stringPassedByValue; } , stringToPassByValue); However, this solution is so verbose that our original function pointer solution is both shorter and easier to read. Update: The full implementation of AsyncCall is too big to post here. In short, what happens is that the AsyncCall template function instantiates a template class holding the lambda function. This class is derived from a base class that contains a virtual Execute() function, and upon an AsyncCall() call, the function call class is put on a call queue. A different thread then executes the queued calls by calling the virtual Execute() function, which is polymorphically dispatched to the template class which then executes the lambda function.

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• css Checkbox Label Selector

  - by HW90

  I'm developing a MVC3 application and need to select the checkboxes label. In ASP MVC3 you have helper methods which creat a part of the code. So the code for a checkbox looks like this: <input id="Jumping_successleicht" type="checkbox" value="true" name="Jumping_successleicht"> <input type="hidden" value="false" name="Jumping_successleicht"> <label for="Jumping_successleicht"> <span>leicht (4)</span> </label> Now I've thought I can use following code to select the label: input[type=checkbox] + label { background: url("../../Images/Controls/Checkbox.png") no-repeat scroll left center transparent; clear: none; cursor: pointer; margin: 0; padding: 5px 0 4px 24px; } But it does not work. It looks like label and input have to be next to each other. Does any ony have a solution how to solve this problem?

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