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• Receving multiple multicast feeds on the same port - C, Linux

  - by Gigi

  I have an application that is receiving data from multiple multicast sources on the same port. I am able to receive the data. However, I am trying to account for statistics of each group (i.e. msgs received, bytes received) and all the data is getting mixed up. Does anyone know how to solved this problem? If I try to look at the sender's address, it is not the multicast address, but rather the IP of the sending machine. I am using the following socket options: struct ip_mreq mreq; mreq.imr_multiaddr.s_addr = inet_addr("224.1.2.3"); mreq.imr_interface.s_addr = INADDR_ANY; setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)); and also: setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &reuse, sizeof(reuse)); I appreciate any help!!!

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• Insriting into a bitstream

  - by evilertoaster

  I'm looking for a way to efficiently insert bits into a bitstream and have it 'overflow', padding with 0's. So for example if you had a byte array with 2 bytes: 231 and 109 (11100111 01101101), and did BitInsert(byteArray,4,00) it would insert two bits at bit offset 4 making 11100001 11011011 01000000 (225,219,24). It would be ok even the method only allowed 1 bit insertions e.g. BitInsert(byteArray,4,true) or BitInsert(byteArray,4,false). I have one method of doing it, but it has to walk the stream with a bitmask bit by bit, so I'm wondering if there's a simpler approach... Answers in assembly or a C derivative would be appreciated.

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• Are indivisible operations still indivisible on multiprocessor and multicore systems?

  - by Steve314

  As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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• fread() behaves weird

  - by Cres

  hi, I have a problem in a C program of mine where after I use fread(), the file pointer goes to the end of the file sometimes. I'll try to explain better - the code looks something like: dummy = ftell(fp); fread(&buf, sizeof(unsigned char), 8, fp); dummy = ftell(fp); where fp is a file pointer to an opened file (opened it with "w+", I'm using it as a binary file and I know i'm supposed to have a "b" in there too, but I heard its not really important to add it..), dummy is just an unsigned long variable, and buf is unsigned char[8] now, when debugging, at the ftell before the fread, dummy is 262062 at the ftell after the fread, dummy is 262640 even though I only 'moved' 8 bytes.. does anyone have any idea what can be the cause of this..? thanks for your help :)

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• Inserting into a bitstream

  - by evilertoaster

  I'm looking for a way to efficiently insert bits into a bitstream and have it 'overflow', padding with 0's. So for example if you had a byte array with 2 bytes: 231 and 109 (11100111 01101101), and did BitInsert(byteArray,4,00) it would insert two bits at bit offset 4 making 11100001 11011011 01000000 (225,219,24). It would be ok even the method only allowed 1 bit insertions e.g. BitInsert(byteArray,4,true) or BitInsert(byteArray,4,false). I have one method of doing it, but it has to walk the stream with a bitmask bit by bit, so I'm wondering if there's a simpler approach... Answers in assembly or a C derivative would be appreciated.

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• About enumerations in Delphi and c++ in 64-bit environments

  - by sum1stolemyname

  I recently had to work around the different default sizes used for enumerations in Delphi and c++ since i have to use a c++ dll from a delphi application. On function call returns an array of structs (or records in delphi), the first element of which is an enum. To make this work, I use packed records (or aligned(1)-structs). However, since delphi selects the size of an enum-variable dynamically by default and uses the smallest datatype possible (it was a byte in my case), but C++ uses an int for enums, my data was not interpreted correctly. Delphi offers a compiler switch to work around this, so the declaration of the enum becomes {$Z4} TTypeofLight = ( V3d_AMBIENT, V3d_DIRECTIONAL, V3d_POSITIONAL, V3d_SPOT ); {$Z1} My Questions are: What will become of my structs when they are compiled on/for a 64-bit environment? Does the default c++ integer grow to 8 Bytes? Are there other memory alignment / data type size modifications (other than pointers)?

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• Software Protection: Shuffeling my application?

  - by Martijn Courteaux

  Hi, I want to continue on my previous question: http://stackoverflow.com/questions/3007168/torrents-can-i-protect-my-software-by-sending-wrong-bytes Developer Art suggested to add a unique key to the application, to identifier the cracker. But JAB said that crackers can search where my unique key is located by checking for binary differences, if the cracker has multiple copies of my software. Then crackers change that key to make them self anonymous. That is true. Now comes the question: If I want to add a unique key, are there tools to shuffle (a kind of obfuscation) the program modules? So, that a binary compare would say that the two files are completely different. So they can't locate the identifier key. I'm pretty sure it is possible (maybe by replacing assembler blocks and make some jumps). I think it would be enough to make 30 to 40 shuffles of my software. Thanks

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• About data size filled in the buffer

  - by Bohan Lu

  I need low-latency audio in my project, and I know Android 2.3 supports OpenSL ES. I have read documents and sample code and I decide to use Android simple buffer queue to do the play and record. I now try to write a simple application to do the test. However, I have some questions about recording. If I set the recorder stop when it is recording, how do I know the exact number of bytes filled in the last buffer if it is not filled up ? In 1.1 version, the callback function has some parameters about buffer and its filled data, but there is no such parameters in version 1.0.1. Is there any way to get this information ? Any suggestion would be greatly appreciated !

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• How do you access byte level information in JavaScript?

  - by JustSmith

  The generally accepted answer is that you can't. However there is mounting evidence that this is not true based on the existence of projects that read in types of data that are not basic HTML types. Some projects that do this are the JavaScript version of ProtoBuf and Smokescreen. Smokescreen is a flash interpreter written in JS so if it is not possible to get at the bytes directly how are these projects working around this? The source to Smokescreen can be found here. I have looked it over but with JS not being my primary language right now the solution eludes me.

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• How is a h264 idea bitstream organized? / header start codes

  - by Wolax

  I was trying to learn a bit about h264 by looking at the bitstream of a video file with a hex editor. I found here the start codes for a video object planes (0x000001b6) and for i-frames (0x000001b600). But I can't find many of those bytes in video files. Most of the time those start codes appear at the beginning of a file with only a few bites in between. I expected them to show up very regularly, in equal distance all over the file!? Is is even ok to look at a file with a hex editor this way? What other start codes exist and how is a h264 file organised?

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• [C++] Wrong EOF when unzipping binary file

  - by djzmo

  Hello there, I tried to unzip a binary file to a membuf from a zip archive using Lucian Wischik's Zip Utils: http://www.wischik.com/lu/programmer/zip_utils.html http://www.codeproject.com/KB/files/zip_utils.aspx FindZipItem(hz, filename.c_str(), true, &j, &ze); char *content = new char[ze.unc_size]; UnzipItem(hz, j, content, ze.unc_size); delete[] content; But it didn't unzip the file correctly. It stopped at the first 0x00 of the file. For example when I unzip an MP3 file, it will only unzip the first 4 bytes: 0x49443303 (ID3\0) because the 5th to 8th byte is 0x00000000. I also tried to capture the ZR_RESULT, and it always return ZR_OK (which means completed without errors). I think this guy also had the same problem, but no one replied to his question: http://www.codeproject.com/KB/files/zip_utils.aspx?msg=2876222#xx2876222xx Any kind of help would be appreciated :)

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• bytea type & nulls, Postgres

  - by Thanatos

  I'm using a bytea type in PostgreSQL, which, to my understanding, contains just a series of bytes. However, I can't get it to play well with nulls. For example: =# select length(E'aa\x00aa'::bytea); length -------- 2 (1 row) I was expecting 5. Also: =# select md5(E'aa\x00aa'::bytea); md5 ---------------------------------- 4124bc0a9335c27f086f24ba207a4912 (1 row) That's the MD5 of "aa", not "aa\x00aa". Clearly, I'm Doing It Wrong, but I don't know what I'm doing wrong. I'm also on an older version of Postgres (8.1.11) for reasons outside of my control. (I'll see if this behaves the same on the latest Postgres as soon as I get home...)

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• Problem calling stored procedure with a fixed length binary parameter using Entity Framework

  - by Dave

  I have a problem calling stored procedures with a fixed length binary parameter using Entity Framework. The stored procedure ends up being called with 8000 bytes of data no matter what size byte array I use to call the function import. To give some example, this is the code I am using. byte[] cookie = new byte[32]; byte[] data = new byte[2]; entities.Insert("param1", "param2", cookie, data); The parameters are nvarchar(50), nvarchar(50), binary(32), varbinary(2000) When I run the code through SQL profiler, I get this result. exec [dbo].[Insert] @param1=N'param1',@param2=N'param2',@cookie=0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 [SNIP because of 16000 zeros] ,@data=0x0000 All parameters went through ok other than the binary(32) cookie. The varbinary(2000) seemed to work fine and the correct length was maintained. Is there a way to prevent the extra data being sent to SQL server? This seems like a big waste of network resource.

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• Reading PGP key information

  - by calccrypto

  can someone show a description of the information of what a pgp looks like if only the descriptions were there but not the actual information? something like (i dont remember if the values are correct): packet-type[4 bits], total length in bytes[16 bits], packet version type [4 bits], creation-time[32 bits], encryption-algorithm[8 bits], ...,etc,etc ive tried to understand rfc4880, but its tedious and confusing. so far, i am think i have extracted the 4 i wrote above, but i cant seem to get the rest of the information out. can anyone help? i know i can just find some pgp program, but the whole point of this is to allow me to learn how those programs work in the first place

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• Determine how much can I write into a filehandle; copying data from one FH to the other.

  - by Vi

  How to determine if I can write the given number of bytes to a filehandle (socket actually)? (Alternatively, how to "unread" the data I had read from other filehandle?) I want something like: n = how_much_can_I_write(w_handle); n = read(r_handle, buf, n); assert(n==write(w_handle, buf, n)); Both filehandles (r_handle and w_handle) have received ready status from epoll_wait. I want all data from r_handle to be copied to w_handle without using a "write debt" buffer. In general, how to copy the data from one filehandle to the other simply and reliably?

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• Determine cluster size of file system in Python

  - by Philip Fourie

  I would like to calculate the "size on disk" of a file in Python. Therefore I would like to determine the cluster size of the file system where the file is stored. How do I determine the cluster size in Python? Or another built-in method that calculates the "size on disk" will also work. I looked at os.path.getsize but it returns the file size in bytes, not taking the FS's block size into consideration. I am hoping that this can be done in an OS independent way...

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• Is there any way to "peek" at a file while it's uploading through HTTP onto a Windows box?

  - by iisystems

  I need to add a file upload function to an ASP.NET website and would like to be able to read a small portion of the file on the server while it's still uploading. A peek or preview type function so I can determine contents and give some feedback to the user while it is still uploading (we're talking about large files here). Is there any way to do this? I'm thinking worst case of writing a custom control which uploads only a fixed number of bytes of the file once chosen and then under the covers starts another upload of the full file. Not totally sure even this is possible, but I'm looking for a more elegant solution anyway... Thanks!

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• MySQL PHP incompatibility.

  - by Evernoob

  Ok maybe I've overlooked something really simple here, but I can't seem to figure this out. I'm running WAMP locally, but connecting to a remote MySQL database. The local version of PHP is the latest 5.3.0. One of the remote databases, being version 5.0.45 works fine. However, the other remote database I'm trying to connect to, which is version 5.0.22 throws the following error before dying: Warning: mysql_connect() [function.mysql-connect]: OK packet 6 bytes shorter than expected. PID=5880 in ... Warning: mysql_connect() [function.mysql-connect]: mysqlnd cannot connect to MySQL 4.1+ using old authentication in ... WTF? UPDATE: Reverting to PHP 5.2.* i.e. anything lower than 5.3.0 resolves the problem completely. As long as I am not running 5.3.0 I can connect to both databases. I'm not sure what the explanation is for this weirdness.

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• Aes key length significance/implications

  - by cppdev

  Hi, I am using a AES algorithm in my application for encrypting plain text. I am trying to use a key which is a six digit number. But as per the AES spec, the key should be minimum sixteen bytes in length. I am planning to append leading zeros to my six digit number to make it a 16 byte and then use this as a key. Would it have any security implications ? I mean will it make my ciphertext more prone to attacks. Please help.

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• Python ctypes argument errors

  - by Patrick Moriarty

  Hello. I wrote a test dll in C++ to make sure things work before I start using a more important dll that I need. Basically it takes two doubles and adds them, then returns the result. I've been playing around and with other test functions I've gotten returns to work, I just can't pass an argument due to errors. My code is: import ctypes import string nDLL = ctypes.WinDLL('test.dll') func = nDLL['haloshg_add'] func.restype = ctypes.c_double func.argtypes = (ctypes.c_double,ctypes.c_double) print(func(5.0,5.0)) It returns the error for the line that called "func": ValueError: Procedure probably called with too many arguments (8 bytes in excess) What am I doing wrong? Thanks.

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• If .net sha1 hash expects a byte array, and php sha1() wants a string, can I match the results?

  - by lynn

  I have a set of bytes I want to apply an sha1 hash to. One hash will be in .net, the other in PHP. Then I'll test to see if they match. In .net, you can create a byte array and use sha.ComputeHash(). byte[] data = new byte[DATA_SIZE]; byte[] result; SHA1 sha = new SHA1CryptoServiceProvider(); // This is one implementation of the abstract class SHA1. result = sha.ComputeHash(data); In PHP, you call sha1($string). I can't do anything about the .net side of the code, but how can I get the same hash out of PHP that .net will generate? Please note: I am ONLY able to work on the PHP side of this. The .net stuff is fixed and can't be modified. Thanks!

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• Is there a concise way to create an InputSupplier for an InputStream in Google Guava?

  - by Fabian Steeg

  There are a few factory methods in Google Guava to create InputSuppliers, e.g. from a byte[]: ByteStreams.newInputStreamSupplier(bytes); Or from a File: Files.newInputStreamSupplier(file); Is there a similar way to to create an InputSupplier for a given InputStream? That is, a way that's more concise than an anonymous class: new InputSupplier<InputStream>() { public InputStream getInput() throws IOException { return inputStream; } }; Background: I'd like to use InputStreams with e.g. Files.copy(...) or ByteStreams.equal(...).

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• Storing CLLocationCoordinates2D in NSMutableArray

  - by Amarsh

  After some searching, I got the following solution : ref: http://stackoverflow.com/questions/1392909/nsmutablearray-addobject-with-mallocd-struct CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D)); new_coordinate->latitude = latitude; new_coordinate->longitude = longitude; [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]]; free(new_coordinate); And access it as: CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes]; However, someone claims that there is a memory leak here? Can anyone suggest me where is the leak and how to fix it. Further, is there a better way of storing a list of CLLocationCoordinate2D in NSMutableArray? Please give sample code since I am an Objective C newbie.

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• How to sanely read and dump structs to disk when some fields are pointers?

  - by bp

  Hello, I'm writing a FUSE plugin in C. I'm keeping track of data structures in the filesystem through structs like: typedef struct { block_number_t inode; filename_t filename; //char[SOME_SIZE] some_other_field_t other_field; } fs_directory_table_item_t; Obviously, I have to read (write) these structs from (to) disk at some point. I could treat the struct as a sequence of bytes and do something like this: read(disk_fd, directory_table_item, sizeof(fs_directory_table_item_t)); ...except that cannot possibly work as filename is actually a pointer to the char array. I'd really like to avoid having to write code like: read(disk_df, *directory_table_item.inode, sizeof(block_number_t)); read(disk_df, directory_table_item.filename, sizeof(filename_t)); read(disk_df, *directory_table_item.other_field, sizeof(some_other_field_t)); ...for each struct in the code, because I'd have to replicate code and changes in no less than three different places (definition, reading, writing). Any DRYer but still maintainable ideas?

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• Error on Access database: Permission denied: 'CreateObject'

  - by elixireu

  Hi, I am migrating a website over to a new server, its in ASP and uses several Access databases, the site and CMS can read, display the data, and even edit and update existing data entries, but when I want to add a new entry, I get an error... Microsoft VBScript runtime error '800a0046' Permission denied: 'CreateObject' /padp2010d/ads_tradetracker.asp, line 11 There seems to be no passwords on the databases, I have set up and tested the ODBC Data Sources and they are working fine. The code or line that is causing the problem is... <% Dim Mail, strPath, strHost, Upload Set Upload = CreateObject("Persits.Upload") Upload.IgnoreNoPost = True ' Generate unique names Upload.OverwriteFiles = False ' Limit file size to 500000 bytes Upload.SetMaxSize 500000, True ' capture an upload and save uploaded files (if any) in temp directory Upload.SaveVirtual "\pa\images\advertenties" Upload.Save ' Use session ID as the new file name NewName = Session.SessionID The line 11 is Set Upload = CreateObject("Persits.Upload") If anyone could help that would be great. Could it be a Permission setting? Im a complete novice with ASP and Access! Thanks

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