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  • c++ class member functions instatiated by traits

    - by Jive Dadson
    I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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  • Python - calendar.timegm() vs. time.mktime()

    - by ibz
    I seem to have a hard time getting my head around this. What's the difference between calendar.timegm() and time.mktime()? Say I have a datetime.datetime with no tzinfo attached, shouldn't the two give the same output? Don't they both give the number of seconds between epoch and the date passed as a parameter? And since the date passed has no tzinfo, isn't that number of seconds the same? >>> import calendar >>> import time >>> import datetime >>> d = datetime.datetime(2010, 10, 10) >>> calendar.timegm(d.timetuple()) 1286668800 >>> time.mktime(d.timetuple()) 1286640000.0 >>>

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  • Php efficiency question --> Database call vs. File Write vs. Calling C++ executable

    - by JP19
    Hi, What I wish to achieve is - log all information about each and every visit to every page ofmy website (like ip address, browser, referring page, etc). Now this is easy to do. What I am interested is doing this in a way so as to cause minimum overhead (runtime) in the php scripts. What is the best approach for this efficiency-wise: 1) Log all information to a database table 2) Write to a file (from php directly) 3) Call a C++ executable, that will write this info to a file in parallel [so the script can continue execution without waiting for the file write to occur ...... is this even possible] I may be trying to optimize unnecessarily/prematurely, but still - any thoughts / ideas on this would be appreciated. (I think efficiency of file write/logging can really be a concern if I have say 100 visits per minute...) Thanks & Regards, JP

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  • Memory issues - Living vs. overall -> app is killed

    - by D33
    I'm trying to check my applications memory issues in Instruments. When I load the application I play some sounds and show some animations in UIImageViews. To save some memory I load the sounds only when I need it and when I stop playing it I free it from the memory. problem 1: My application is using about 5.5MB of Living memory. BUT The Overall section is growing after start to 20MB and then it's slowly growing (about 100kB/sec). But responsible Library is OpenAL (OAL::Buffer), dyld (_dyld_start)-I am not sure what this really is, and some other stuff like ft_mem_qrealloc, CGFontStrikeSetValue, … problem 2: When the overall section breaks about 30MB, application crashes (is killed). According to the facts I already read about overall memory, it means then my all allocations and deallocation is about 30MB. But I don't really see the problem. When I need some sound for example I load it to the memory and when I don't need it anymore I release it. But that means when I load 1MB sound, this operation increase overall memory usage with 2MB. Am I right? And when I load 10 sounds my app crashes just because the fact my overall is too high even living is still low??? I am very confused about it. Could someone please help me clear it up? (I am on iOS 5 and using ARC) SOME CODE: creating the sound OpenAL: MYOpenALSound *sound = [[MyOpenALSound alloc] initWithSoundFile:filename willRepeat:NO]; if(!sound) return; [soundDictionary addObject:sound]; playing: [sound play]; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, ((sound.duration * sound.pitch) + 0.1) * NSEC_PER_SEC), dispatch_get_current_queue(), ^{ [soundDictionary removeObjectForKey:[NSNumber numberWithInt:soundID]]; }); } creating the sound with AVAudioPlayer: [musics replaceObjectAtIndex:ID_MUSIC_MAP withObject:[[Music alloc] initWithFilename:@"mapMusic.mp3" andWillRepeat:YES]]; pom = [musics objectAtIndex:musicID]; [pom playMusic]; and stop and free it: [musics replaceObjectAtIndex:ID_MUSIC_MAP withObject:[NSNull null]]; AND IMAGE ANIMATIONS: I load images from big PNG file (this is realated also to my other topic : Memory warning - UIImageView and its animations) I have few UIImageViews and by time I'm setting animation arrays to play Animations... UIImage *source = [[UIImage alloc] initWithCGImage:[[UIImage imageNamed:@"imageSource.png"] CGImage]]; cutRect = CGRectMake(0*dimForImg.width,1*dimForImg.height,dimForImg.width,dimForImg.height); image1 = [[UIImage alloc] initWithCGImage:CGImageCreateWithImageInRect([source CGImage], cutRect)]; cutRect = CGRectMake(1*dimForImg.width,1*dimForImg.height,dimForImg.width,dimForImg.height); ... image12 = [[UIImage alloc] initWithCGImage:CGImageCreateWithImageInRect([source CGImage], cutRect)]; NSArray *images = [[NSArray alloc] initWithObjects:image1, image2, image3, image4, image5, image6, image7, image8, image9, image10, image11, image12, image12, image12, nil]; and this array I just use simply like : myUIImageView.animationImages = images, ... duration -> startAnimating

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  • Receiving broadcast packets using packet socket

    - by user314336
    Hello I try to send DHCP RENEW packets to the network and receive the responses. I broadcast the packet and I can see that it's successfully sent using Wireshark. But I have difficulties receiving the responses.I use packet sockets to catch the packets. I can see that there are responses to my RENEW packet using Wireshark, but my function 'packet_receive_renew' sometimes catch the packets but sometimes it can not catch the packets. I set the file descriptor using FDSET but the 'select' in my code can not realize that there are new packets for that file descriptor and timeout occurs. I couldn't make it clear that why it sometimes catches the packets and sometimes doesn't. Anybody have an idea? Thanks in advance. Here's the receive function. int packet_receive_renew(struct client_info* info) { int fd; struct sockaddr_ll sock, si_other; struct sockaddr_in si_me; fd_set rfds; struct timeval tv; time_t start, end; int bcast = 1; int ret = 0, try = 0; char buf[1500] = {'\0'}; uint8_t tmp[BUFLEN] = {'\0'}; struct dhcp_packet pkt; socklen_t slen = sizeof(si_other); struct dhcps* new_dhcps; memset((char *) &si_me, 0, sizeof(si_me)); memset((char *) &si_other, 0, sizeof(si_other)); memset(&pkt, 0, sizeof(struct dhcp_packet)); define SERVER_AND_CLIENT_PORTS ((67 << 16) + 68) static const struct sock_filter filter_instr[] = { /* check for udp */ BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9), BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 0, 4), /* L5, L1, is UDP? */ /* skip IP header */ BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0), /* L5: */ /* check udp source and destination ports */ BPF_STMT(BPF_LD|BPF_W|BPF_IND, 0), BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, SERVER_AND_CLIENT_PORTS, 0, 1), /* L3, L4 */ /* returns */ BPF_STMT(BPF_RET|BPF_K, 0x0fffffff ), /* L3: pass */ BPF_STMT(BPF_RET|BPF_K, 0), /* L4: reject */ }; static const struct sock_fprog filter_prog = { .len = sizeof(filter_instr) / sizeof(filter_instr[0]), /* casting const away: */ .filter = (struct sock_filter *) filter_instr, }; printf("opening raw socket on ifindex %d\n", info->interf.if_index); if (-1==(fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP)))) { perror("packet_receive_renew::socket"); return -1; } printf("got raw socket fd %d\n", fd); /* Use only if standard ports are in use */ /* Ignoring error (kernel may lack support for this) */ if (-1==setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog, sizeof(filter_prog))) perror("packet_receive_renew::setsockopt"); sock.sll_family = AF_PACKET; sock.sll_protocol = htons(ETH_P_IP); //sock.sll_pkttype = PACKET_BROADCAST; sock.sll_ifindex = info->interf.if_index; if (-1 == bind(fd, (struct sockaddr *) &sock, sizeof(sock))) { perror("packet_receive_renew::bind"); close(fd); return -3; } if (-1 == setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &bcast, sizeof(bcast))) { perror("packet_receive_renew::setsockopt"); close(fd); return -1; } FD_ZERO(&rfds); FD_SET(fd, &rfds); tv.tv_sec = TIMEOUT; tv.tv_usec = 0; ret = time(&start); if (-1 == ret) { perror("packet_receive_renew::time"); close(fd); return -1; } while(1) { ret = select(fd + 1, &rfds, NULL, NULL, &tv); time(&end); if (TOTAL_PENDING <= (end - start)) { fprintf(stderr, "End receiving\n"); break; } if (-1 == ret) { perror("packet_receive_renew::select"); close(fd); return -4; } else if (ret) { new_dhcps = (struct dhcps*)calloc(1, sizeof(struct dhcps)); if (-1 == recvfrom(fd, buf, 1500, 0, (struct sockaddr*)&si_other, &slen)) { perror("packet_receive_renew::recvfrom"); close(fd); return -4; } deref_packet((unsigned char*)buf, &pkt, info); if (-1!=(ret=get_option_val(pkt.options, DHO_DHCP_SERVER_IDENTIFIER, tmp))) { sprintf((char*)tmp, "%d.%d.%d.%d", tmp[0],tmp[1],tmp[2],tmp[3]); fprintf(stderr, "Received renew from %s\n", tmp); } else { fprintf(stderr, "Couldnt get DHO_DHCP_SERVER_IDENTIFIER%s\n", tmp); close(fd); return -5; } new_dhcps->dhcps_addr = strdup((char*)tmp); //add to list if (info->dhcps_list) info->dhcps_list->next = new_dhcps; else info->dhcps_list = new_dhcps; new_dhcps->next = NULL; } else { try++; tv.tv_sec = TOTAL_PENDING - try * TIMEOUT; tv.tv_usec = 0; fprintf(stderr, "Timeout occured\n"); } } close(fd); printf("close fd:%d\n", fd); return 0; }

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  • Programming for a 32-bit environment vs programming for a 64-bit environment / Build configurations

    - by Russel
    I was looking at some same code (a sample MS Visual Studio C++ project) recently with multiple build configurations (Release/Debug, Win32/x64). My question: What is the difference? I guess I understand Release/Debug (Release = finalized version of project, Debug = version used to run in debugger), but what things need to be considered when building different versions for Win32/x64 platforms? Is there any coding differences, or does this just affect how that same code is ultimately built into machine code? I know there are different library files depending on whether you're using a 32-bit or 64-bit system as well... Are all of these differences again just machine code? Would a 32-bit library file and its corresponding 64-bit library file be two files with exactly the same functions build from the same source code originally, and only differing in their machine code implementation? Thanks! --Russel

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  • Cursors vs Procedures in SQL

    - by CogitoErgoSum
    So, I just learned about CURSORS but still don't exactly grasp them. What is the difference between a cursor and procedure or even a function? So far from the various examples (DECLARE CURSOR ... SELECT ... FROM ...) It seems at most its a variable to hold a query. Is the data real time, or a snapshot of when the cursor was declared? i.e. I have a table with one row and one col with a value of 2. I do DECLARE CURSOR ... SELECT * FROM table1 I then insert a new row with a value of 3. When I run the cursor, would I Just get the one row from before the cursor was declared, or both rows? Thanks

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  • Huge page buffer vs. multiple simultaneous processes

    - by Andrei K.
    One of our customer has a 35 Gb database with average active connections count about 70-80. Some tables in database have more than 10M records per table. Now they have bought new server: 4 * 6 Core = 24 Cores CPU, 48 Gb RAM, 2 RAID controllers 256 Mb cache, with 8 SAS 15K HDD on each. 64bit OS. I'm wondering, what would be a fastest configuration: 1) FB 2.5 SuperServer with huge buffer 8192 * 3500000 pages = 29 Gb or 2) FB 2.5 Classic with small buffer of 1000 pages. Maybe some one has tested such case before and will save me days of work :) Thanks in advance.

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  • Permission issue when webservice deployed as virtual directory.Works in VS IDE

    - by Shyju
    I have an ASP.NET web service which will create a text file in a path which is being passed as a parameter to the method. private void CreateFile(string path) { string strFileName = path; StreamWriter sw = new StreamWriter(strFileName, true); sw.WriteLine(""); sw.Write("Created at " + DateTime.Now.ToString()); sw.Close(); } Now I am passing a folder in the network as the parameter and calling the method CreateFile(@"\\192.168.0.40\\labels\\test.txt"); When running the code from the Visual studio IDE,the file is getting created in the path.But when i published this and deployed as a virtual directoty,Its throwing me some error like "System.UnauthorizedAccessException: Access to the path '\\192.168.0.40\labels\test.txt' is denied. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy) at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options) at System.IO.StreamWriter.CreateFile(String path, Boolean append) at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize) at System.IO.StreamWriter..ctor(String path, Boolean append) I have in my web.config.My machine is running in XP and the other is in Windows Server 2003 Any idea to solve this ?? Thanks in advance

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  • Interpreted vs. Compiled vs. Late-Binding

    - by zubin71
    Python is compiled into an intermediate bytecode(pyc) and then executed. So, there is a compilation followed by interpretation. However, long-time Python users say that Python is a "late-binding" language and that it should`nt be referred to as an interpreted language. How would Python be different from another interpreted language? Could you tell me what "late-binding" means, in the Python context? Java is another language which first has source code compiled into bytecode and then interpreted into bytecode. Is Java an interpreted/compiled language? How is it different from Python in terms of compilation/execution? Java is said to not have, "late-binding". Does this have anything to do with Java programs being slighly faster than Python? Itd be great if you could also give me links to places where people have already discussed this; id love to read more on this. Thank you.

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  • SEO Google - Navigation Title vs. Page Heading

    - by louism
    Hi, i was wondering if anyone knows if theres a connection between what a navigation item is named and the page heading it goes to - does this have an impact on SEO? so for example, if i had in my navigation menu an item called About Us, but when you click it you come to a page with the heading Learn Who We Are (i.e. wrapped in [h1] heading tags) because there isnt an exact one-to-one match, is that a bad thing in terms of SEO? thanks

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  • Script Speed vs Memory Usage

    - by Doug Neiner
    I am working on an image generation script in PHP and have gotten it working two ways. One way is slow but uses a limited amount of memory, the second is much faster, but uses 6x the memory . There is no leakage in either script (as far as I can tell). In a limited benchmark, here is how they performed: -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 65.626 | 540,036 | 200 Two | 20.207 | 3,269,600 | 200 -------------------------------------------- And here is the average of the previous numbers (if you don't want to do your own math): -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 0.328 | 540,036 | 1 Two | 0.101 | 3,269,600 | 1 -------------------------------------------- Which method should I use and why? I anticipate this being used by a high volume of users, with each user making 10-20 requests to this script during a normal visit. I am leaning toward the faster method because though it uses more memory, it is for a 1/3 of the time and would reduce the number of concurrent requests.

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  • StringBuilder/StringBuffer vs. "+" Operator

    - by matt.seil
    I'm reading "Better, Faster, Lighter Java" (by Bruce Tate and Justin Gehtland) and am familiar with the readability requirements in agile type teams, such as what Robert Martin discusses in his clean coding books. On the team I'm on now, I've been told explicitly not to use the "+" operator because it creates extra (and unnecessary) string objects during runtime. But this article: http://www.ibm.com/developerworks/java/library/j-jtp01274.html Written back in '04 talks about how object allocation is about 10 machine instructions. (essentially free) It also talks about how the GC also helps to reduce costs in this environment. What is the actual performance tradeoffs between using "+," "StringBuilder," or "StringBuffer?" (In my case it is StringBuffer only as we are limited to Java 1.4.2.) StringBuffer to me results in ugly, less readable code, as a couple of examples in Tate's book demonstrates. And StringBuffer is thread-synchronized which seems to have its own costs that outweigh the "danger" in using the "+" operator. Thoughts/Opinions?

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  • Storing DateTime (UTC) vs. storing DateTimeOffset

    - by Frederico
    I usually have an "interceptor" that right before reading/writing from/to the database does datetime conversion (from UTC to localtime, and from localtime to utc), so I can use DateTime.Now (derivations and comparisions) throughout the system without worrying about timezones. Regarding serialization and moving data between computers, there is no need to bother, as the datetime is always UTC. Should I continue storing my dates (SQL 2008 - datetime) in UTC format or should I instead store it using DateTimeOffset (SQL 2008 - datetimeoffset)? UTC Dates in the database (datetime type) have been working and known for so long, why change it? What are the advantages? I have already looked into articles like this one, but I'm not 100% convinced though. Any thoughts?

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  • Should I call class destructor in this code?

    - by peterg
    I am using this sample to decode/encode some data I am retrieving/sending from/to a web server, and I want to use it like this: BOOL HandleMessage(UINT uMsg,WPARAM wParam,LPARAM lParam,LRESULT* r) { if(uMsg == WM_DESTROY) { PostQuitMessage(0); return TRUE; } else if(uMsg == WM_CREATE) { // Start timer StartTimer(); return TRUE; } else if(uMsg == WM_TIMER) { //get data from server char * test = "test data"; Base64 base64; char *temp = base64.decode(test); MessageBox(TEXT(temp), 0, 0); } } The timer is set every 5 minutes. Should I use delete base64 at the end? Does delete deallocates everything used by base64?

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  • xgettext vs gettext

    - by Kentor
    I have a few questions: I know what gettext is. I've read a few posts where they mentioned xgettext and was curious as to what is the difference between the two. How can I install xgettext on Windows? And finally, does anybody have a tutorial on how to install the library php-gettext http://savannah.nongnu.org/projects/php-gettext/ (this one usually doesn't come with PHP) I've read about it in an article but I'm not sure how to get it working in Windows. The thing is, sometimes when you make changes, you need to restart Apache to see the new data with the gettext that comes with PHP (but with the library you don't need to restart it) so I wanted to use the library for development. Thanks!

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  • Building vs. Compiling (Java)

    - by sixtyfootersdude
    Thinking that the answer to this is pretty obvious but here it goes: When I am working on a small project for school (in java) I "compile" it. On my coop we are using ant to "build" our project. I think that compiling is a subset of building. Is this correct? What is the difference between building and compiling?

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