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  • fastest way to crawl recursive ntfs directories in C++

    - by Peter Parker
    I have written a small crawler to scan and resort directory structures. It based on dirent(which is a small wrapper around FindNextFileA) In my first benchmarks it is surprisingy slow: around 123473ms for 4500 files(thinkpad t60p local samsung 320 GB 2.5" HD). 121481 files found in 123473 milliseconds Is this speed normal? This is my code: int testPrintDir(std::string strDir, std::string strPattern="*", bool recurse=true){ struct dirent *ent; DIR *dir; dir = opendir (strDir.c_str()); int retVal = 0; if (dir != NULL) { while ((ent = readdir (dir)) != NULL) { if (strcmp(ent->d_name, ".") !=0 && strcmp(ent->d_name, "..") !=0){ std::string strFullName = strDir +"\\"+std::string(ent->d_name); std::string strType = "N/A"; bool isDir = (ent->data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) !=0; strType = (isDir)?"DIR":"FILE"; if ((!isDir)){ //printf ("%s <%s>\n", strFullName.c_str(),strType.c_str());//ent->d_name); retVal++; } if (isDir && recurse){ retVal += testPrintDir(strFullName, strPattern, recurse); } } } closedir (dir); return retVal; } else { /* could not open directory */ perror ("DIR NOT FOUND!"); return -1; } }

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  • Problem with linking in gcc

    - by chitra
    I am compiling a program in which a header file is defined in multiple places. Contents of each of the header file is different, though the variable names are the same internal members within the structures are different . Now at the linking time it is picking up from a library file which belongs to a different header not the one which is used during compilation. Due to this I get an error at link time. Since there are so many libraries with the same name I don't know which library is being picked up. I have lot of oems and other customized libraries which are part of this build. I checked out the options in gcc which talks about selecting different library files to be included. But no where I am able to see an option which talks about which libraries are being picked up the linker. If the linker is able to find more than one library file name, then which does the linker pick up is something which I am not able to understand. I don't want to specify any path, rather I want to understand how the linker is resolving the multiple libraries that it is able to locate. I tried putting -v option, but that doesn't list out the path from which the gcc picks up the library. I am using gcc on linux. Any help in this regard is highly appreciated. Regards, Chitra

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  • forcing stack w/i 32bit when -m64 -mcmodel=small

    - by chaosless
    have C sources that must compile in 32bit and 64bit for multiple platforms. structure that takes the address of a buffer - need to fit address in a 32bit value. obviously where possible these structures will use natural sized void * or char * pointers. however for some parts an api specifies the size of these pointers as 32bit. on x86_64 linux with -m64 -mcmodel=small tboth static data and malloc()'d data fit within the 2Gb range. data on the stack, however, still starts in high memory. so given a small utility _to_32() such as: int _to_32( long l ) { int i = l & 0xffffffff; assert( i == l ); return i; } then: char *cp = malloc( 100 ); int a = _to_32( cp ); will work reliably, as would: static char buff[ 100 ]; int a = _to_32( buff ); but: char buff[ 100 ]; int a = _to_32( buff ); will fail the assert(). anyone have a solution for this without writing custom linker scripts? or any ideas how to arrange the linker section for stack data, would appear it is being put in this section in the linker script: .lbss : { *(.dynlbss) *(.lbss .lbss.* .gnu.linkonce.lb.*) *(LARGE_COMMON) } thanks!

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  • Hashtable resizing leaks memory

    - by thpetrus
    I wrote a hashtable and it basically consists of these two structures: typedef struct dictEntry { void *key; void *value; struct dictEntry *next; } dictEntry; typedef struct dict { dictEntry **table; unsigned long size; unsigned long items; } dict; dict.table is a multidimensional array, which contains all the stored key/value pair, which again are a linked list. If half of the hashtable is full, I expand it by doubling the size and rehashing it: dict *_dictRehash(dict *d) { int i; dict *_d; dictEntry *dit; _d = dictCreate(d->size * 2); for (i = 0; i < d->size; i++) { for (dit = d->table[i]; dit != NULL; dit = dit->next) { _dictAddRaw(_d, dit); } } /* FIXME memory leak because the old dict can never be freed */ free(d); // seg fault return _d; } The function above uses the pointers from the old hash table and stores it in the newly created one. When freeing the old dict d a Segmentation Fault occurs. How am I able to free the old hashtable struct without having to allocate the memory for the key/value pairs again?

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  • What should be taught in a "Fundamentals of programming" course at university?

    - by Dervin Thunk
    I have started a new question (see here), because I think the topic is of importance in a more general form. The question is now: If you were a professor at a Computer Science Dept. in some university, what would make it into your course? This is a programming course, second term, first year computer science/computer engineering. Remember you have a limited amount of time, and students are of different levels of competence, and some may be scientists, but some will also go on to be programmers in companies of different kinds. You have to cater to all. Bonus: What language? (Although see this question for my current thoughts about this...) Maybe you want to attach a course outline from some university? See here for an even more general question about this. Answer: I can't really summarize this post... I guess it was too subjective. However, it looks like we have to cover the history of computing up to a certain extent, computer architecture (memory, registers, whatever), C, and finally some basic algos and data structures in a problem solving fashion. This will be the bare bones of the course. Thanks all. I will accept the most voted up answer to close the thread, as it should be done.

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  • How to scale a PHP application (servers, mysql, memcache)

    - by Stéphane Goetz
    Hi, I'm currently creating a website for a social project in switzerland. And before there is an overflow of user, I want to prepare the application to scale. I answered by myself many questions but some are left. I explain what I want to do. First at the beginnning, the Application will have only one server (short time) with DNS, PHP, Mysql, Data, and memcache. Second Then I will split them in two DNS, Mysql, memcache Data, PHP Third Here is the problem, I don't know how to do it exactly here to keep the application running well. I could do : Front : Load Balancer, memcache, DNS Web 1 : PHP, DATA Web 2 : PHP, DATA Mysql This would be the scheme, all PHP sessions are kept in the DB. BUT, how do I sync the data? do I run a Rsync to keep them up to date. do I put them on a separate disk (network disk) to be sure ? but in this case, how can I do in case of user uploads ? and if the website gets more success and we have to go on greater structures, would'nt it create some latency on updates ? or would it be a good thing to go directly to amazon's web services ? some infos I use codeigniter as Framework. I use linux as webserver (distribution not chosen now, but should be Debian) Thanks in advance for your answers.

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  • C/C++ Control Structure Limitations?

    - by STingRaySC
    I have heard of a limitation in VC++ (not sure which version) on the number of nested if statements (somewhere in the ballpark of 300). The code was of the form: if (a) ... else if (b) ... else if (c) ... ... I was surprised to find out there is a limit to this sort of thing, and that the limit is so small. I'm not looking for comments about coding practice and why to avoid this sort of thing altogether. Here's a list of things that I'd imagine could have some limitation: Number of functions in a scope (global, class, or namespace). Number of expressions in a single statement (e.g., compound conditionals). Number of cases in a switch. Number of parameters to a function. Number of classes in a single hierarchy (either inheritance or containment). What other control structures/language features have limits such as this? Do the language standards say anything about these limits (perhaps minimum requirements for an implementation)? Has anyone run into a particular language limitation like this with a particular compiler/implementation? EDIT: Please note that the above form of if statements is indeed "nested." It is equivalent to: if (a) { //... } else { if (b) { //... } else { if (c) { //... } else { //... } } }

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  • how to elegantly duplicate a graph (neural network)

    - by macias
    I have a graph (network) which consists of layers, which contains nodes (neurons). I would like to write a procedure to duplicate entire graph in most elegant way possible -- i.e. with minimal or no overhead added to the structure of the node or layer. Or yet in other words -- the procedure could be complex, but the complexity should not "leak" to structures. They should be no complex just because they are copyable. I wrote the code in C#, so far it looks like this: neuron has additional field -- copy_of which is pointer the the neuron which base copied from, this is my additional overhead neuron has parameterless method Clone() neuron has method Reconnect() -- which exchanges connection from "source" neuron (parameter) to "target" neuron (parameter) layer has parameterless method Clone() -- it simply call Clone() for all neurons network has parameterless method Clone() -- it calls Clone() for every layer and then it iterates over all neurons and creates mappings neuron=copy_of and then calls Reconnect to exchange all the "wiring" I hope my approach is clear. The question is -- is there more elegant method, I particularly don't like keeping extra pointer in neuron class just in case of being copied! I would like to gather the data in one point (network's Clone) and then dispose it completely (Clone method cannot have an argument though).

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  • Why is debugging better in an IDE?

    - by Bill Karwin
    I've been a software developer for over twenty years, programming in C, Perl, SQL, Java, PHP, JavaScript, and recently Python. I've never had a problem I could not debug using some careful thought, and well-placed debugging print statements. I respect that many people say that my techniques are primitive, and using a real debugger in an IDE is much better. Yet from my observation, IDE users don't appear to debug faster or more successfully than I can, using my stone knives and bear skins. I'm sincerely open to learning the right tools, I've just never been shown a compelling advantage to using visual debuggers. Moreover, I have never read a tutorial or book that showed how to debug effectively using an IDE, beyond the basics of how to set breakpoints and display the contents of variables. What am I missing? What makes IDE debugging tools so much more effective than thoughtful use of diagnostic print statements? Can you suggest resources (tutorials, books, screencasts) that show the finer techniques of IDE debugging? Sweet answers! Thanks much to everyone for taking the time. Very illuminating. I voted up many, and voted none down. Some notable points: Debuggers can help me do ad hoc inspection or alteration of variables, code, or any other aspect of the runtime environment, whereas manual debugging requires me to stop, edit, and re-execute the application (possibly requiring recompilation). Debuggers can attach to a running process or use a crash dump, whereas with manual debugging, "steps to reproduce" a defect are necessary. Debuggers can display complex data structures, multi-threaded environments, or full runtime stacks easily and in a more readable manner. Debuggers offer many ways to reduce the time and repetitive work to do almost any debugging tasks. Visual debuggers and console debuggers are both useful, and have many features in common. A visual debugger integrated into an IDE also gives you convenient access to smart editing and all the other features of the IDE, in a single integrated development environment (hence the name).

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  • How would you implement a hashtable in language x?

    - by mk
    The point of this question is to collect a list of examples of hashtable implementations using arrays in different languages. It would also be nice if someone could throw in a pretty detailed overview of how they work, and what is happening with each example. Edit: Why not just use the built in hash functions in your specific language? Because we should know how hash tables work and be able to implement them. This may not seem like a super important topic, but knowing how one of the most used data structures works seems pretty important to me. If this is to become the wikipedia of programming, then these are some of the types of questions that I will come here for. I'm not looking for a CS book to be written here. I could go pull Intro to Algorithms off the shelf and read up on the chapter on hash tables and get that type of info. More specifically what I am looking for are code examples. Not only for me in particular, but also for others who would maybe one day be searching for similar info and stumble across this page. To be more specific: If you had to implement them, and could not use built-in functions, how would you do it? You don't need to put the code here. Put it in pastebin and just link it.

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  • table subtraction challenge

    - by Valentin
    I have a challenge that I haven’t overcome in the last two days using Stored Procedures and SQL 2008. I took several approaches but must fell short. One appraoch very interesting was using a table substraction. It’s really all about table subtraction. I was wondering if you could help me crack this one. Here is the challenge: Two tables 1Testdb y 2Testdb. My first step was to select ID relationships ([2Testdb].Acc_id) on table 2Testdb for one given individual ([2Testdb].Bus_id). Then query table 1Testdb for records not mathcing my original selection from 2Testdb. But other approaches are welcome. Data and Structures: USE [Challengedb] GO SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[1Testdb]( [Acc_id] [uniqueidentifier] NULL [Name] [Varchar(10)] NULL ) ON [PRIMARY] GO CREATE TABLE [dbo].[2Testdb]( [Acc_id] [uniqueidentifier] NULL, [Bus_id] [uniqueidentifier] NULL ) ON [PRIMARY] GO Records on 1Testdb: 34455F60-9474-4521-804E-66DB39A579F3, John C23523F6-2309-4F58-BB3F-EF7486C7AF8B, Pete DC711615-3BE4-4B31-9EF2-B1314185CA62, Dave E3AAB073-2398-476D-828B-92829F686A4C, Adam Records on 2Testdb: (Relationship table, ex. Friend relationships) Record #1: DC711615-3BE4-4B31-9EF2-B1314185CA62, 34455F60-9474-4521-804E-66DB39A579F3 Record #2: E3AAB073-2398-476D-828B-92829F686A4C, 34455F60-9474-4521-804E-66DB39A579F3 Record # 3: DC711615-3BE4-4B31-9EF2-B1314185CA62, E3AAB073-2398-476D-828B-92829F686A4C Record # 4: E3AAB073-2398-476D-828B-92829F686A4C, DC711615-3BE4-4B31-9EF2-B1314185CA62 Challenge: Select from table 1Testdb only those records distinct that may not have a relationship with John [34455F60-9474-4521-804E-66DB39A579F3] on table 2Testdb. Expected result should be (Who does John doesn’t have relationship with?): C23523F6-2309-4F58-BB3F-EF7486C7AF8B, Pete Thank you, Valentin

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  • Indices instead of pointers in STL containers?

    - by zvrba
    Due to specific requirements [*], I need a singly-linked list implementation that uses integer indices instead of pointers to link nodes. The indices are always interpreted with respect to a vector containing the list nodes. I thought I might achieve this by defining my own allocator, but looking into the gcc's implementation of , they explicitly use pointers for the link fields in the list nodes (i.e., they do not use the pointer type provided by the allocator): struct _List_node_base { _List_node_base* _M_next; ///< Self-explanatory _List_node_base* _M_prev; ///< Self-explanatory ... } (For this purpose, the allocator interface is also deficient in that it does not define a dereference function; "dereferencing" an integer index always needs a pointer to the underlying storage.) Do you know a library of STL-like data structures (i am mostly in need of singly- and doubly-linked list) that use indices (wrt. a base vector) instead of pointers to link nodes? [*] Saving space: the lists will contain many 32-bit integers. With two pointers per node (STL list is doubly-linked), the overhead is 200%, or 400% on 64-bit platform, not counting the overhead of the default allocator.

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  • how to change ASP.NET Configuration tool connection string

    - by Zviadi
    Hello, how can I change ASP.NET Configuration tool-s connection string name? (Which connection string will ASP.NET Configuration tool will use) I'm learning ASP.NET and everywhere and in book that I'm reading now theres connection string named: LocalSqlServer. I want to use my local sql server database instead of sql express to store Roles, Membership and other data. I have used aspnet_regsql.exe to create needed data structures in my database. after that I changed my web.config to look like: <connectionStrings> <remove name="LocalSqlServer"/> <add name="LocalSqlServer" connectionString="Server=(LOCAL); Database=MyDatabase;Integrated Security=True" providerName="System.Data.SqlClient" /> </connectionStrings> but when I run ASP.NET Configuration tool it says that: "The connection name 'ApplicationServices' was not found in the applications configuration or the connection string is empty." ASP.NET Configuration tool uses connection string named: ApplicationServices not LocalSqlServer. cause of that I have to modify web.config to: <connectionStrings> <add name="ApplicationServices" connectionString="Server=(LOCAL); Database=MyDatabase;Integrated Security=True" providerName="System.Data.SqlClient" /> </connectionStrings> and everything works fine. I wish to know why the hell my web site uses connection string named: ApplicationServices and all books and online documentations uses LocalSqlServer? and how to change it to LocalSqlServer? I have: Windows 7 Sql Server 2008 R2 Visual Studio 2010 Premium Project type is website

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  • Fastest inline-assembly spinlock

    - by sigvardsen
    I'm writing a multithreaded application in c++, where performance is critical. I need to use a lot of locking while copying small structures between threads, for this I have chosen to use spinlocks. I have done some research and speed testing on this and I found that most implementations are roughly equally fast: Microsofts CRITICAL_SECTION, with SpinCount set to 1000, scores about 140 time units Implementing this algorithm with Microsofts InterlockedCompareExchange scores about 95 time units Ive also tried to use some inline assembly with __asm {} using something like this code and it scores about 70 time units, but I am not sure that a proper memory barrier has been created. Edit: The times given here are the time it takes for 2 threads to lock and unlock the spinlock 1,000,000 times. I know this isn't a lot of difference but as a spinlock is a heavily used object, one would think that programmers would have agreed on the fastest possible way to make a spinlock. Googling it leads to many different approaches however. I would think this aforementioned method would be the fastest if implemented using inline assembly and using the instruction CMPXCHG8B instead of comparing 32bit registers. Furthermore memory barriers must be taken into account, this could be done by LOCK CMPXHG8B (I think?), which guarantees "exclusive rights" to the shared memory between cores. At last [some suggests] that for busy waits should be accompanied by NOP:REP that would enable Hyper-threading processors to switch to another thread, but I am not sure whether this is true or not? From my performance-test of different spinlocks, it is seen that there is not much difference, but for purely academic purpose I would like to know which one is fastest. However as I have extremely limited experience in the assembly-language and with memory barriers, I would be happy if someone could write the assembly code for the last example I provided with LOCK CMPXCHG8B and proper memory barriers in the following template: __asm { spin_lock: ;locking code. spin_unlock: ;unlocking code. }

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  • Dynamically invoke web service at runtime

    - by Ulrik Rasmussen
    So, our application needs support for dynamically calling web services which are unknown at compile time. The user should therefore be able to specify a URL to a WSDL, and specify some data bindings for the request and reply parameters. When Googling for answers, it seems like the way to do this is by actually compiling a web service proxy class at runtime, loading it, and invoking the methods using reflection. I think this seems like a rather clunky approach, given that I don't really need a strongly typed set of classes when I'm going to cast my data dynamically anyway. Dynamically compiling code for doing something that simple also just seems like The Wrong Way To Do It. Restricting ourself to the SOAP protocol, is there any library for C# that implements this protocol for dynamic use? I can imagine that it would be possible to generate runtime key/value data structures from the WSDL, which could be used to specify the request messages, as well as reading the replies. The library should then be able to send well-formed SOAP messages to the server, and parse the replies, without the programmer having to generate the XML manually (at least not the headers and other plumbing). I can't seem to find any library that actually does this. Is what I want to do really that esoteric, or have I just searched the wrong places? Thanks, Ulrik

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  • Where do objects merge/join data in a 3-tier model?

    - by BerggreenDK
    Its probarbly a simple 3-tier problem. I just want to make sure we use the best practice for this and I am not that familiary with the structures yet. We have the 3 tiers: GUI: ASP.NET for Presentation-layer (first platform) BAL: Business-layer will be handling the logic on a webserver in C#, so we both can use it for webforms/MVC + webservices DAL: LINQ to SQL in the Data-layer, returning BusinessObjects not LINQ. DB: The SQL will be Microsoft SQL-server/Express (havent decided yet). Lets think of setup where we have a database of [Persons]. They can all have multiple [Address]es and we have a complete list of all [PostalCode] and corresponding citynames etc. The deal is that we have joined a lot of details from other tables. {Relations}/[tables] [Person]:1 --- N:{PersonAddress}:M --- 1:[Address] [Address]:N --- 1:[PostalCode] Now we want to build the DAL for Person. How should the PersonBO look and when does the joins occure? Is it a business-layer problem to fetch all citynames and possible addressses pr. Person? or should the DAL complete all this before returning the PersonBO to the BAL ? Class PersonBO { public int ID {get;set;} public string Name {get;set;} public List<AddressBO> {get;set;} // Question #1 } // Q1: do we retrieve the objects before returning the PersonBO and should it be an Array instead? or is this totally wrong for n-tier/3-tier?? Class AddressBO { public int ID {get;set;} public string StreetName {get;set;} public int PostalCode {get;set;} // Question #2 } // Q2: do we make the lookup or just leave the PostalCode for later lookup? Can anyone explain in what order to pull which objects? Constructive criticism is very welcome. :o)

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  • New record may be written twice in clusterd index structure

    - by Cupidvogel
    As per the article at Microsoft, under the Test 1: INSERT Performance section, it is written that For the table with the clustered index, only a single write operation is required since the leaf nodes of the clustered index are data pages (as explained in the section Clustered Indexes and Heaps), whereas for the table with the nonclustered index, two write operations are required—one for the entry into the index B-tree and another for the insert of the data itself. I don't think that is necessarily true. Clustered Indexes are implemented through B+ tree structures, right? If you look at at this article, which gives a simple example of inserting into a B+ tree, we can see that when 8 is initially inserted, it is written only once, but then when 5 comes in, it is written to the root node as well (thus written twice, albeit not initially at the time of insertion). Also when 8 comes in next, it is written twice, once at the root and then at the leaf. So won't it be correct to say, that the number of rewrites in case of a clustered index is much less compared to a NIC structure (where it must occur every time), instead of saying that rewrite doesn't occur in CI at all?

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  • Splitting a set of object into several subsets of 'similar' objects

    - by doublep
    Suppose I have a set of objects, S. There is an algorithm f that, given a set S builds certain data structure D on it: f(S) = D. If S is large and/or contains vastly different objects, D becomes large, to the point of being unusable (i.e. not fitting in allotted memory). To overcome this, I split S into several non-intersecting subsets: S = S1 + S2 + ... + Sn and build Di for each subset. Using n structures is less efficient than using one, but at least this way I can fit into memory constraints. Since size of f(S) grows faster than S itself, combined size of Di is much less than size of D. However, it is still desirable to reduce n, i.e. the number of subsets; or reduce the combined size of Di. For this, I need to split S in such a way that each Si contains "similar" objects, because then f will produce a smaller output structure if input objects are "similar enough" to each other. The problems is that while "similarity" of objects in S and size of f(S) do correlate, there is no way to compute the latter other than just evaluating f(S), and f is not quite fast. Algorithm I have currently is to iteratively add each next object from S into one of Si, so that this results in the least possible (at this stage) increase in combined Di size: for x in S: i = such i that size(f(Si + {x})) - size(f(Si)) is min Si = Si + {x} This gives practically useful results, but certainly pretty far from optimum (i.e. the minimal possible combined size). Also, this is slow. To speed up somewhat, I compute size(f(Si + {x})) - size(f(Si)) only for those i where x is "similar enough" to objects already in Si. Is there any standard approach to such kinds of problems? I know of branch and bounds algorithm family, but it cannot be applied here because it would be prohibitively slow. My guess is that it is simply not possible to compute optimal distribution of S into Si in reasonable time. But is there some common iteratively improving algorithm?

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  • How can I eliminate latency in quicktime streamed video

    - by JJFeiler
    I'm prototyping a client that displays streaming video from a HaiVision Barracuda through a quicktime client. I've been unable to reduce the buffer size below 3.0 seconds... for this application, we need as low a latency as the network allows, and prefer video dropouts to delay. I'm doing the following: - (void)applicationDidFinishLaunching:(NSNotification *)aNotification { NSString *path = [[NSBundle mainBundle] pathForResource:@"haivision" ofType:@"sdp"]; NSError *error = nil; QTMovie *qtmovie = [QTMovie movieWithFile:path error:&error]; if( error != nil ) { NSLog(@"error: %@", [error localizedDescription]); } Movie movie = [qtmovie quickTimeMovie]; long trackCount = GetMovieTrackCount(movie); Track theTrack = GetMovieTrack(movie,1); Media theMedia = GetTrackMedia(theTrack); MediaHandler theMediaHandler = GetMediaHandler(theMedia); QTSMediaPresentationParams myPres; ComponentResult c = QTSMediaGetIndStreamInfo(theMediaHandler, 1,kQTSMediaPresentationInfo, &myPres); Fixed shortdelay = 1<<15; OSErr theErr = QTSPresSetInfo (myPres.presentationID, kQTSAllStreams, kQTSTargetBufferDurationInfo, &shortdelay ); NSLog(@"OSErr %d", theErr); [movieView setMovie:qtmovie]; [movieView play:self]; } I seem to be getting valid objects/structures all the way down to the QTSPres, though the ComponentResult and OSErr are both returning -50. The streaming video plays fine, but the buffer is still 3.0seconds. Any help/insight appreciated. J

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  • Populating and Using Dynamic Classes in C#/.NET 4.0

    - by Bob
    In our application we're considering using dynamically generated classes to hold a lot of our data. The reason for doing this is that we have customers with tables that have different structures. So you could have a customer table called "DOG" (just making this up) that contains the columns "DOGID", "DOGNAME", "DOGTYPE", etc. Customer #2 could have the same table "DOG" with the columns "DOGID", "DOG_FIRST_NAME", "DOG_LAST_NAME", "DOG_BREED", and so on. We can't create classes for these at compile time as the customer can change the table schema at any time. At the moment I have code that can generate a "DOG" class at run-time using reflection. What I'm trying to figure out is how to populate this class from a DataTable (or some other .NET mechanism) without extreme performance penalties. We have one table that contains ~20 columns and ~50k rows. Doing a foreach over all of the rows and columns to create the collection take about 1 minute, which is a little too long. Am I trying to come up with a solution that's too complex or am I on the right track? Has anyone else experienced a problem like this? Create dynamic classes was the solution that a developer at Microsoft proposed. If we can just populate this collection and use it efficiently I think it could work.

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  • Building "isolated" and "automatically updated" caches (java.util.List) in Java.

    - by Aidos
    Hi Guys, I am trying to write a framework which contains a lot of short-lived caches created from a long-living cache. These short-lived caches need to be able to return their entier contents, which is a clone from the original long-living cache. Effectively what I am trying to build is a level of transaction isolation for the short-lived caches. The user should be able to modify the contents of the short-lived cache, but changes to the long-living cache should not be propogated through (there is also a case where the changes should be pushed through, depending on the Cache type). I will do my best to try and explain: master-cache contains: [A,B,C,D,E,F] temporary-cache created with state [A,B,C,D,E,F] 1) temporary-cache adds item G: [A,B,C,D,E,F] 2) temporary-cache removes item B: [A,C,D,E,F] master-cache contains: [A,B,C,D,E,F] 3) master-cache adds items [X,Y,Z]: [A,B,C,D,E,F,X,Y,Z] temporary-cache contains: [A,C,D,E,F] Things get even harder when the values in the items can change and shouldn't always be updated (so I can't even share the underlying object instances, I need to use clones). I have implemented the simple approach of just creating a new instance of the List using the standard Collection constructor on ArrayList, however when you get out to about 200,000 items the system just runs out of memory. I know the value of 200,000 is excessive to iterate, but I am trying to stress my code a bit. I had thought that it might be able to somehow "proxy" the list, so the temporary-cache uses the master-cache, and stores all of it's changes (effectively a Memento for the change), however that quickly becomes a nightmare when you want to iterate the temporary-cache, or retrieve an item at a specific index. Also given that I want some modifications to the contents of the list to come through (depending on the type of the temporary-cache, whether it is "auto-update" or not) and I get completly out of my depth. Any pointers to techniques or data-structures or just general concepts to try and research will be greatly appreciated. Cheers, Aidos

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  • Why doesn't the Java Collections API include a Graph implementation?

    - by dvanaria
    I’m currently learning the Java Collections API and feel I have a good understanding of the basics, but I’ve never understood why this standard API doesn’t include a Graph implementation. The three base classes are easily understandable (List, Set, and Map) and all their implementations in the API are mostly straightforward and consistent. Considering how often graphs come up as a potential way to model a given problem, this just doesn’t make sense to me (it’s possible it does exist in the API and I’m not looking in the right place of course). Steve Yegge suggests in one of his blog posts that a programmer should consider graphs first when attacking a problem, and if the problem domain doesn’t fit naturally into this data structure, only then consider the alternative structures. My first guess is that there is no universal way to represent graphs, or that their interfaces may not be generic enough for an API implementation to be useful? But if you strip down a graph to its basic components (vertices and a set of edges that connect some or all of the vertices) and consider the ways that graphs are commonly constructed (methods like addVertex(v) and insertEdge(v1, v2)) it seems that a generic Graph implementation would be possible and useful. Thanks for helping me understand this better.

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  • Is XSLT worth investing time in and are there any actual alternatives?

    - by Keeno
    I realize this has been a few other questions on this topic, and people are saying use your language of choice to manipulate the XML etc etc however, not quite fit my question exactly. Firstly, the scope of the project: We want to develop platform independent e-learning, currently, its a bunch of HTML pages but as they grow and develop they become hard to maintain. The idea: Generate up an XML file + Schema, then produce some XSLT files that process the XML into the eLearning modiles. XML to HTML via XSLT. Why: We would like the flexibilty to be able to easy reformat the content (I realize CSS is a viable alternative here) If we decide to alter the pages layout or functionality in anyway, im guessing altering the "shared" XSLT files would be easier than updating the HTML files. So far, we have about 30 modules, with up to 10-30 pages each Depending on some "parameters" we could output drastically different page layouts/structures, above and beyond what CSS can do Now, all this has to be platform independent, and to be able to run "offline" i.e. without a server powering the HTML Negatives I've read so far for XSLT: Overhead? Not exactly sure why...is it the compute power need to convert to HTML? Difficult to learn Better alternatives Now, what I would like to know exactly is: are there actually any viable alternatives for this "offline"? Am I going about it in the correct manner, do you guys have any advice or alternatives. Thanks!

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  • Avoid an "out of memory error" in Java(eclipse), when using large data structure?

    - by gnomed
    OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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  • Cant print contents of a custom file

    - by ZaZu
    Hello, Im trying to scan contents from a random file into an array in a structure. Then I want to print those contents on screen. (NOTE: The following code is from a bigger program, this is just a sample, but all structures and arrays used are needed as declared ) The contents of the file being tested are simply: 5 4 3 2 5 3 4 2 #include<stdio.h> #define first 500 #define sec 500 struct trial{ int f; int r; float what[first][sec]; }; int trialtest(trial *test); int trialdisplay(trial *test); main(){ trial test; trialtest(&test); trialdisplay(&test); } int trialtest(trial *test){ int z,x,i; FILE *inputf; inputf=fopen("randomfile.txt","r"); for(i=0;i<5;i++){ fscanf(inputf,"%f",&(*test).what[z][x]); } fclose(inputf); return 0; } int trialdisplay(trial *test){ int i,z,x; printf("printing\n\n\n"); for (i=0;i<10;i++){ printf("%f",(*test).what[z][x]); } return 0; } The problem is, I get this error whenever I run the code .. I cant really understand whats going on : Any suggestions ? Thanks alot !

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