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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• How do I determine darker or lighter color variant of a given color?

  - by Nidonocu

  Given a source color of any hue by the system or user, I'd like a simple algorithm I can use to work out a lighter or darker variants of the selected color. Similar to effects used on Windows Live Messenger for styling the user interface. Language is C# with .net 3.5. Responding to comment: Color format is (Alpha)RGB. With values as bytes or floats. Marking answer: For the context of my use (a few simple UI effects), the answer I'm marking as accepted is actually the most simple for this context. However, I've given up votes to the more complex and accurate answers too. Anyone doing more advanced color operations and finding this thread in future should definitely check those out. Thanks SO. :)

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• convert flv to mp3 with Java

  - by krial

  Hi, I'm pretty new in developing programs in Java. I'm currently writing a program that converts a flv video into mp3. I have already written such a program in Visual Studio.net C#, but the Problem is, that it isn't cross platform compatible... I used the ffmpeg binary to convert the video into mp3, but I can't find ffmpeg binaries for Mac and Linux. (if so, I could start the specific binaries from java, depending on the OS) So I tried to convert the video with Xuggle, but the final mp3 has 0 bytes. My current code is the following: IMediaReader reader = ToolFactory.makeReader("video.flv"); reader.addListener(ToolFactory.makeWriter("music.mp3", reader)); while (reader.readPacket() == null) do {} while(false); Thanks in advance. p.s sorry for my bad english

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• Swap byte 2 and 4 from integer

  - by czar x

  I had this interview question - Swap byte 2 and byte4 within an integer sequence. Integer is a 4byte wide i.e. 32 bits My approach was to use char *pointer and a temp char to swap the bytes. For clarity i have broken the steps otherwise an character array can be considered. unsigned char *b2, *b4, tmpc; int n = 0xABCD; b2 = &n; b2++; b4 = &n; b4 +=3; ///swap the values; tmpc = *b2; *b2 = *b4; *b4 = tmpc; Any other methods?

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• Java - Does null variable require space in memory

  - by Yatendra Goel

  class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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• A Computer Poem for those over 30 [closed]

  - by arvind

  I recd. a very good poem, that i wished to share with everyone. so for once we need no answers. lol ;-) A computer was something on TV From a science fiction show of note A window was something you hated to clean And ram was the cousin of a goat. Meg was the name of my girlfriend And gig was a job for the nights Now they all mean different things And that really mega bytes. An application was for employment A program was a TV show A cursor used profanity A keyboard was a piano.

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• argument promotions in C function calls

  - by HaoCheng

  I learned from ----As to when default promotions kick in: default argument promotions are used exactly when the expected type of the argument is unknown, which is to say when there's no prototype or when the argument is variadic. But an example confusing me is: void func(char a, char b) { printf("a=%p,b=%p\n",&a,&b); } int main(void) { char a=0x11,b=0x22; func(a,b); return 0; } It is cleard in the above example: when calling func in main, there is no need to promote the arguments a and b, but the output shows &a = &b +4 not &a = &b+1. If no promotion occured, why 4 bytes between two CHAR argument?

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• Protocol/Packet Design Questions

  - by cam

  I'm looking to a design a protocol for a client-server application and need some links to some resources that may help me. The big part is I'm trying to create my own "packet" format so I can minimize the amount of information being sent. I'm looking for some resources to dissect their protocol, but it seems some completely lack packet design, such as SMTP (which just sends strings terminated by CLRF). What are the advantages/disadvantages of using a system like SMTP over a system that uses a custom made packet? Couldn't SMTP use only a couple bytes to cover all commands through bit flags and save bandwidth/space? Just trying to get my head around all this.

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• Splitting string into array upon token

  - by Gnutt

  I'm writing a script to perform an offsite rsync backup, and whenever the rsyncline recieves some output it goes into a single variable. I then want to split that variable into an array upon the ^M token, so that I can send them to two different logger-sessions (so I get them on seperate lines in the log). My current line to perform the rsync result=rsync --del -az -e "ssh -i $cert" $source $destination 2>&1 Result in the log, when the server is unavailable ssh: connect to host offsite port 22: Connection timed out^M rsync: connection unexpectedly closed (0 bytes received so far) [sender] rsync error: unexplained error (code 255) at io.c(601) [sender=3.0.7]

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• In Perl, can I limit the length of a line as I read it in from a file (like fgets)

  - by SB

  I'm trying to write a piece of code that reads a file line by line and stores each line, up to a certain amount of input data. I want to guard against the end-user being evil and putting something like a gig of data on one line in addition to guarding against sucking in an abnormally large file. Doing $str = <FILE> will still read in a whole line, and that could be very long and blow up my memory. fgets lets me do this by letting me specify a number of bytes to read during each call and essentially letting me split one long line into my max length. Is there a similar way to do this in perl? I saw something about sv_gets but am not sure how to use it (though I only did a cursory Google search). Thanks.

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• What .NET UnmanagedType is Unicode (UTF-16)?

  - by Pat

  I am packing bytes into a struct, and some of them correspond to a Unicode string. The following works fine for an ASCII string: [StructLayout(LayoutKind.Sequential)] private struct PacketBytes { [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)] public string MyString; } I assumed that I could do [StructLayout(LayoutKind.Sequential)] private struct PacketBytes { [MarshalAs(UnmanagedType.LPWStr, SizeConst = 32)] public string MyString; } to make it Unicode, but that didn't work. (Since this field is part of a struct with other fields, which I've omitted for clarity, I can't simply change the CharSet of the containing struct.) Any idea what I'm doing wrong?

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• (iphone) maintaining CGContextRef or CGLayerRef is a bad idea?

  - by Eugene

  Hi, I need to work with many images, and I can't hold them as UIImage in memory because they are too big. I also need to change colors of image and merge them on the fly. Creating UIImage from underlying NSData, change color, and combine them when you can't have many images on memory is fairly slow. (as far as I can get) I thought maybe I can store underlying CGLayerRef(for image that will be combined) and CGContextRef(the resulting combined image). I am new to drawing world, and not sure if CGLayerRef or CGContextRef is smaller in memory than UIImage. I recently heard that w*h image takes up w*h*4 bytes in memory. Does CGLayerRef or CGContextRef also take up that much memory? Thank you

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• Extract data from uint8 to double

  - by HADJ AMOR HASSEN

  I have a C function receiving a uint8 pointer with another parameter which is its size (number of bytes). I want to extract double data from this buffer. Here is my code: Write(uint8* data, uint8 size) /* data and size are given by a callback to my function)*/ { double d; for (i = 0; i < size; i++) { d = ((double*)&data)[i]; printf(" d = %d\n"); } } The problem is that I am not receiving what I am sending within an external hardware. I guess that my cast is wrong. I tried other methods but without any good result. I am still not able to get what I send.

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• Operations on 64bit words in 32bit system

  - by Vilo

  I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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• What is/are the Scala way(s) to implement this Java "byte[] to Hex" class

  - by nicerobot

  I'm specifically interested in Scala (2.8) techniques for building strings with formats as well as interesting ways to make such a capability easily accessible where it's useful (lists of bytes, String, ...?).. public class Hex { public static String valueOf (final byte buf[]) { if (null == buf) { return null; } final StringBuilder sb = new StringBuilder(buf.length * 2); for (final byte b : buf) { sb.append(String.format("%02X", b & 0xff)); } return sb.toString(); } public static String valueOf (final Byteable o) { return valueOf(o.toByteArray()); } } This is only a learning exercise (so the utility and implementation of the Java isn't a concern.) Thanks

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• WAVEFORMATEX - how to read codecdata at the end??

  - by Roey

  Hi All. I've a WAVEFORMATEX struct with some codecdata at the end of it (10 bytes). I'm using C++. How do I access the data at the end? (this is a purely technical question). I tried : WAVEFORMATEX* wav = (WAVEFORMATEX*)pmt->pbFormat; WORD me = wav->cbSize; wav = wav + sizeof(WAVEFORMATEX); BYTE* arr = new BYTE[me]; memcpy(arr, (BYTE*)wav, me); Didnt work. Thanks Roey

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• C# Struct No Parameterless Constructor? See what I need to accomplish

  - by Changeling

  I am using a struct to pass to an unmanaged DLL as so - [StructLayout(LayoutKind.Sequential)] public struct valTable { public byte type; public byte map; public byte spare1; public byte spare2; public int par; public int min; public byte[] name; public valTable() { name = new byte[24]; } } The code above will not compile because VS 2005 will complain that "Structs cannot contain explicit parameterless constructors". In order to pass this struct to my DLL, I have to pass an array of struct's like so valTable[] val = new valTable[281]; What I would like to do is when I say new, the constructor is called and it creates an array of bytes like I am trying to demonstrate because the DLL is looking for that byte array of size 24 in each dimension. How can I accomplish this?

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• Using sizeof with a dynamically allocated array

  - by robUK

  Hello, gcc 4.4.1 c89 I have the following code snippet: #include <stdlib.h> #include <stdio.h> char *buffer = malloc(10240); /* Check for memory error */ if(!buffer) { fprintf(stderr, "Memory error\n"); return 1; } printf("sizeof(buffer) [ %d ]\n", sizeof(buffer)); However, the sizeof(buffer) always prints 4. I know that a char* is only 4 bytes. However, I have allocated the memory for 10kb. So shouldn't the size be 10240? I am wondering am I thinking right here? Many thanks for any suggestions,

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• C (or C++?) Syntax: STRUCTTYPE varname = {0};

  - by Jared Updike

  Normally one would declare/allocate a struct on the stack with?: STRUCTTYPE varname; What does this syntax mean in C (or is this C++ only, or perhaps specific to VC++)? STRUCTTYPE varname = {0}; where STRUCTTYPE is the name of a stuct type, like RECT or something. This code compiles and it seems to just zero out all the bytes of the struct but I'd like to know for sure if anyone has a reference. Also, is there a name for this construct?

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• Read a file to multiple array byte[]

  - by hankol

  I have an encryption algorithm (AES) that accepts file converted to array byte and encrypt it. Since I am going to process a very big size files, the JVM may go out of memory. I am planing to read the files in multiple array byte. each containing some part of the file. Then I teratively feed the algorithm. Finally merge them to produce encrypted file. So my question is: there any way to read a file part by part to multiple array byte? I thought I can use the following to read the file to array byte: IOUtils.toByteArray(InputStream input). And then split the array into multiple bytes using: Arrays.copyOfRange(). But I am afraid that the first code that reads file to byte will make the JVM to go out of memory. any suggestion please ? thanks

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• Database table schema design - varchar(n). Suitable choice of N

  - by morpheous

  Coming from a C background, I may be getting too anal about this and worrying unnecessarily about bits and bytes here. Still, I cant help thinking how the data is actually stored and that if I choose an N which is easily factorizable into a power of 2, the database will be more effecient in how it packs data etc. Using this "logic", I have a string field in a table which is a variable length up to 21 chars. I am tempted to use 32 instead of 21, for the reason given above - however now I am thinking that I am wasting disk space because there will be space allocated for 11 extra chars that are guaranteed to be never used. Since I envisage storing several tens of thousands of rows a day, it all adds up. Question: Mindful of all of the above, Should I declare varchar(21) or varchar(32) and why?

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• What weird encoding is movistar Venezuela sms on blackberry using?

  - by cjp

  Send an sms using the normal GSM TextMessage API on the BlackBerry, get back garbage. It's not unicode, phone is set to 7-bit send. Byte size is only off by one. Is there some default crypto thing, or some weird encoding they use? This code works most everywhere else in the world; this definitely seems like a movistar problem. The string that comes back is random 7-bit ascii except for a few high order bytes. Needless to say the source input text is totally 7 bit chars, which should work in sms, ISO-8859 and look the same in UTF charsets. Anybody seen this or got sms working in code on movistar VZ blackberries?

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• Continuously reading from a stream in C#?

  - by Damien Wildfire

  I have a Stream object that occasionally gets some data on it, but at unpredictable intervals. Messages that appear on the Stream are well-defined and declare the size of their payload in advance (the size is a 16-bit integer contained in the first two bytes of each message). I'd like to have a StreamWatcher class which detects when the Stream has some data on it. Once it does, I'd like an event to be raised so that a subscribed StreamProcessor instance can process the new message. Can this be done with C# events without using Threads directly? It seems like it should be straightforward, but I can't get quite get my head around the right way to design this.

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• gcc compiled binaries w/different sizes?

  - by BillTorpey

  If the same code is built at different times w/gcc, the resulting binary will have different contents. OK, I'm not wild about that, but that's what it is. However, I've recently run into a situation where the same code, built with the same version of gcc, is generating a binary with a different size than a prior build (by about 1900 bytes). Does anyone have any idea what may be causing either of these situations? Is this some kind of ELF issue? Are there any tools out there (other than ldd) that can be used to dump contents of binaries to see what exactly is different? Thanks in advance.

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• How much RAM used by Python dict or list?

  - by Who8MyLunch

  My problem: I am writing a simple Python tool to help me visualize my data as a function of many parameters. Each change in parameters involves a non-trivial amount of time, so I would like to cache each step's resulting imagery and supporting data in a dictionary. But then I worry that this dictionary could grow too large over time. Most of my data is in the form of Numpy arrays. My question: How would one go about computing the total number of bytes used by a Python dictionary. The dictionary itself may contain lists and other dictionaries, each of which contain data stored in Numpy arrays. Ideas?

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