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  • Unix Piping using Fork and Dup

    - by Jacob
    Lets say within my program I want to execute two child processes, one to to execute a "ls -al" command and then pipe that into "wc" command and display the output on the terminal. How can I do this using pipe file descriptors so far the code I have written: An example would be greatly helpful int main(int argc, char *argv[]) { int pipefd[2] pipe(pipefd2); if ((fork()) == 0) { dup2(pipefd2[1],STDOUT_FILENO); close(pipefd2[0]); close(pipefd2[1]); execl("ls", "ls","-al", NULL); exit(EXIT_FAILURE); } if ((fork()) == 0){ dup2(pipefd2[0],STDIN_FILENO); close(pipefd2[0]); close(pipefd2[1]); execl("/usr/bin/wc","wc",NULL); exit(EXIT_FAILURE); } close(pipefd[0]); close(pipefd[1]); close(pipefd2[0]); close(pipefd2[1]); }

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  • Best way to store sales tax information

    - by Seph
    When designing a stock management database system (sales / purchases) what would be the best way to store the various taxes and other such amounts? A few of the fields that could be saved are: Unit price excluding tax Unit price including tax Tax per item Total excluding tax (rounded to 2 decimals) Total including tax (rounded to 2 decimals) Total tax (rounded to 2 decimals) Currently the most reasonable solution so far is storing down (roughly) item, quantity, total excluding tax (rounded) and the total tax (rounded). Can anyone suggest some better way of storing this details for a generic system? Also, given the system needs to be robust, what should be done if there were multiple tax values (eg: state and city) which might need to be separated, in this case a separate table would be in order, but would it be considered excessive to just have a rowID and some taxID mapping to a totalTax column?

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  • What is a great tool for remote pair development?

    - by Haim Bender
    I'm looking for something like VNC, but with some extra features: The server should send only the part of the screen the client is looking at. It would be great if we could have 2 mice on the client's desktop. Or at least if the client could point to somthing without interrupting the server's mouse. A shared whiteboard would be great. Some extra notes: My friend lives far away, and we are using WinXP.

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  • What is the best algorithm for this problem?

    - by mark
    What is the most efficient algorithm to solve the following problem? Given 6 arrays, D1,D2,D3,D4,D5 and D6 each containing 6 numbers like: D1[0] = number D2[0] = number ...... D6[0] = number D1[1] = another number D2[1] = another number .... ..... .... ...... .... D1[5] = yet another number .... ...... .... Given a second array ST1, containing 1 number: ST1[0] = 6 Given a third array ans, containing 6 numbers: ans[0] = 3, ans[1] = 4, ans[2] = 5, ......ans[5] = 8 Using as index for the arrays D1,D2,D3,D4,D5 and D6, the number that goes from 0, to the number stored in ST1[0] minus one, in this example 6, so from 0 to 6-1, compare each res array against each D array My algorithm so far is: I tried to keep everything unlooped as much as possible. EML := ST1[0] //number contained in ST1[0] EML1 := 0 //start index for the arrays D While EML1 < EML if D1[ELM1] = ans[0] goto two if D2[ELM1] = ans[0] goto two if D3[ELM1] = ans[0] goto two if D4[ELM1] = ans[0] goto two if D5[ELM1] = ans[0] goto two if D6[ELM1] = ans[0] goto two ELM1 = ELM1 + 1 return 0 //bad row of numbers, if while ends two: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[1] goto two if D2[ELM1] = ans[1] goto two if D3[ELM1] = ans[1] goto two if D4[ELM1] = ans[1] goto two if D5[ELM1] = ans[1] goto two if D6[ELM1] = ans[1] goto two ELM1 = ELM1 + 1 return 0 three: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[2] goto two if D2[ELM1] = ans[2] goto two if D3[ELM1] = ans[2] goto two if D4[ELM1] = ans[2] goto two if D5[ELM1] = ans[2] goto two if D6[ELM1] = ans[2] goto two ELM1 = ELM1 + 1 return 0 four: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[3] goto two if D2[ELM1] = ans[3] goto two if D3[ELM1] = ans[3] goto two if D4[ELM1] = ans[3] goto two if D5[ELM1] = ans[3] goto two if D6[ELM1] = ans[3] goto two ELM1 = ELM1 + 1 return 0 five: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[4] goto two if D2[ELM1] = ans[4] goto two if D3[ELM1] = ans[4] goto two if D4[ELM1] = ans[4] goto two if D5[ELM1] = ans[4] goto two if D6[ELM1] = ans[4] goto two ELM1 = ELM1 + 1 return 0 six: EML1 := 0 start index for arrays Ds While EML1 < EML if D1[ELM1] = ans[0] return 1 //good row of numbers if D2[ELM1] = ans[0] return 1 if D3[ELM1] = ans[0] return 1 if D4[ELM1] = ans[0] return 1 if D5[ELM1] = ans[0] return 1 if D6[ELM1] = ans[0] return 1 ELM1 = ELM1 + 1 return 0 As language of choice, it would be pure c

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  • Naming Suggestions For A Function Providing Chaining In A Different Way

    - by sid3k
    I've coded an experimental function which makes passed objects chainable by using high order functions. It's name is "chain" for now, and here is a usage example; chain("Hello World") (print) // evaluates print function by passing "Hello World" object. (console.log,"Optional","Parameters") (returnfrom) // returns "Hello World" It looks lispy but behaves very different since it's coded in a C based language, I don't know if there is a name for this idiom and I couldn't any name more suitable than "chain". Any ideas, suggestions?

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  • How do I program hardware?

    - by Arlen Beiler
    What would I need to program a piece of hardware to do something for me? Let's say I have something with 15 relays (or equivalent) and I want to tell it to turn off relay 10. Or better yet, when sensor 10 is activated, toggle relay 10.

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  • How to counter the "one true language" perspective?

    - by Rob Wells
    How do you work with someone when they haven't been able to see that there is a range of other languages out there beyond "The One True Path"? I mean someone who hasn't realised that the modern software professional has a range of tools in his toolbox. The person whose knee jerk reaction is, for example, "We must do this is C++!" "Everything must be done in C++!" What's the best approach to open people up to the fact that "not everything is a nail"? How may I introduce them to having a well-equipped toolbox, selecting the best tool for the job at hand?

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  • User Mode Linux - Installing a module error

    - by Zach
    I am trying to run 'make' on a module in User Mode Linux to install a simple makefile. Here is my make file: obj-m := hello.o KDIR := /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules When I run this in User Mode Linux I get the following error: make[1]: Entering directory /lib/modules/2.6.28/build' make[1]: *** No rule to make targetmodules'. Stop. make[1]: Leaving directory `/lib/modules/2.6.28/build' make: * [default] Error 2 The problem is that no files are present under /lib/modules/. There's no directory for 2.6.28 or build. From what I've read, these should be symlinks to /usr/src, but under /usr/src, I don't see any files under that either.

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  • Writing to Socket outputStream w/o closing it

    - by Eyal
    Hi, I'd like to write some messages to the server. Each time, for the tramsmitting only, I'm closing the outputStream and reopen it when I have to send the next message. os.write(msgBytes); os.write("\r\n".getBytes()); os.flush(); os.close(); How Can I keep this Socket's OutputStream, os, open and still be able to send the message? Thanks.

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  • Parallel computing for integrals

    - by Iman
    I want to reduce the calculation time for a time-consuming integral by splitting the integration range. I'm using C++, Windows, and a quad-core Intel i7 CPU. How can I split it into 4 parallel computations?

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  • F# exercise help - Beginner

    - by bobjink
    I hope you can help me with these exercises I have been stuck with. I am not in particular looking for the answers. Tips that help me solve them myself are just as good :) 1. Write a function implode : char list - string so that implode s returns the characters concatenated into a string: let implode (cArray:char list) = List.foldBack (+) 0 cArray;; Error. I am thinking that i need to cast every char to strings before I do the above. I bet however, that there is a much simpler and better solution. 2. Write a function palindrome : string - bool, so that palindrome s returns true if the string s is a palindrome let isIdentical cArray1 cArray2 = (cArray1 = cArray2);; let palinDrome (word:string) = isIdentical(word.ToCharArray(), Array.rev(word.ToCharArray()));; I get the value: val palinDrome : string - (char [] * char [] - bool), which is not what I want. 3. Write a function combinePair : int list - int list so that combinePair xs returns the list with elements from xs combined into pairs. If xs contains an odd number of elements, then the last element is thrown away: I have no idea for this one.

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  • Explaining persistent data structures in simple terms

    - by Jason Baker
    I'm working on a library for Python that implements some persistent data structures (mainly as a learning exercise). However, I'm beginning to learn that explaining persistent data structures to people unfamiliar with them can be difficult. Can someone help me think of an easy (or at least the least complicated) way to describe persistent data structures to them? I've had a couple of people tell me that the documentation that I have is somewhat confusing. (And before anyone asks, no I don't mean persistent data structures as in persisted to the file system. Google persistent data structures if you're unclear on this.)

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  • Why do static Create methods exist?

    - by GeReV
    I was wondering, why do static Create methods exist? For instance, why use this code: System.Xml.XmlReader reader = System.Xml.XmlReader.Create(inputUri); over this code: System.Xml.XmlReader reader = new System.Xml.XmlReader(inputUri); I cannot find the rationale for using one over the other, and can't find any relation between classes who use this construct over the other. Can anyone shed some light on this?

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  • Function overloading by return type?

    - by dsimcha
    Why don't more mainstream statically typed languages support function/method overloading by return type? I can't think of any that do. It seems no less useful or reasonable than supporting overload by parameter type. How come it's so much less popular?

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  • How to handle Socket Exception ideally?

    - by cbz
    Hi, I'm using socket for chat application and I get SocketException unexpectedly. How this exception should ideally be handled? I'm currently simply reconnecting socket. How to make sure my socket is live on application level? I'm aware of method setKeepAlive

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  • How do I write to a file and print to a terminal cuncurrently in Unix?

    - by bias
    I have a little bash function to log my Macports outputs to a file (since installs often spew little tidbits that are easy to lose in terminal noise), then I just cat the file to the terminal: function porti { command sudo port install $@ >> $1.log 2>&1; cat $1.log } Is there a way to do this concurrently? I don't care about it being in Bash, that's just how I started it. BTW I pass $@ to install but only $1 for the file name so that I can do something like: porti git-gore +bash_completion and only get the file git-core.log however someone else might prefer to include variants in the file name ...

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  • seperating interface and implemention with normal functions

    - by ace
    this seems like it should be pretty simple, im probably leaving something simple out. this is the code im trying to run. it is 3 files, 2*cpp and 1*header. -------------lab6.h ifndef LAB6_H_INCLUDED define LAB6_H_INCLUDED int const arraySize = 10; int array1[arraySize]; int array2[arraySize]; void generateArray(int[], int ); void displayArray(int[], int[], int ); void reverseOrder(int [],int [], int); endif // LAB6_H_INCLUDED -----------------lab6.cpp include using std::cout; using std::endl; include using std::rand; using std::srand; include using std::time; include using std::setw; include "lab6.h" void generateArray(int array1[], int arraySize) { srand(time(0)); for (int i=0; i<10; i++) { array1[i]=(rand()%10); } } void displayArray(int array1[], int array2[], int arraySize) { cout<<endl<<"Array 1"<<endl; for (int i=0; i<arraySize; i++) { cout<<array1[i]<<", "; } cout<<endl<<"Array 2"<<endl; for (int i=0; i<arraySize; i++) { cout<<array2[i]<<", "; } } void reverseOrder(int array1[],int array2[], int arraySize) { for (int i=0, j=arraySize-1; i<arraySize;j--, i++) { array2[j] = array1[i]; } } ------------and finally main.cpp include "lab6.h" int main() { generateArray(array1, arraySize); reverseOrder(array1, array2, arraySize); displayArray(array1, array2, arraySize); return 0; }

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  • Pattern Matching in Scheme

    - by kunjaan
    How do I accept the following input? (list of 0 or more charcters and ends with 3) or (list of 1 or more characters 4 and 0 or more characters after 4) something like (match ( list 3)) -> #t (match ( list 1 2 3)) -> #t (match (list 1 2 3 4)) -> #t (match (list 1 2 3 4 5)) -> #t (match (list 4)) -> #f EDIT: THIS IS NOT MY HOMEWORK. I trying to write something like ELIZA from PAIP but I know only how to write a pattern that begins with a word.

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  • shell script passing arguments

    - by arav
    From the wrapper shell scripts i am calling the Java program. I want the Unix shell script to pass all the arguments to java program except the EMAIL argument. HOW Can i remove the EMAIL argument and pass the rest of the arguments to the java program. EMAIL argument can come at any position. valArgs() { until [ $# -eq 0 ]; do case $1 in -EMAIL) MAILFLAG=Y shift break ;; esac done } main() { valArgs "$@" $JAVA_HOME/bin/java -d64 -jar WEB-INF/lib/test.jar "$@"

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  • What languages have a while-else type control structure, and how does it work?

    - by Dan
    A long time ago, I thought I saw a proposal to add an else clause to for or while loops in C or C++... or something like that. I don't remember how it was supposed to work -- did the else clause run if the loop exited normally but not via a break statement? Anyway, this is tough to search for, so I thought maybe I could get some CW answers here for various languages. What languages support adding an else clause to something other than an if statement? What is the meaning of that clause? One language per answer please.

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  • SocketTimeOutException while creating socket, java

    - by Sunil Kumar Sahoo
    Hi All, I have created a sample java socket application. I used Socket s = new Socket(ip, port) Now it works fine. but when my internet connection is very slow that time after a long interval (even if sometimes after 2 minutes) i used to get SocketTimeOutException in that line. means it gives that error while creating socket. I want the exception should be handled properly means if internet connection is very slow then if that error occurs it happens very late now . I want if this type of error occurs then it should be caught very fast means the error should not come at such a delay interval of time rather it should come immediately. How to achieve this. Thanks Sunil Kumar Sahoo

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  • Self Assesstment Tests for Programmers

    - by THX1138.6
    I want to help the Dev team identify areas of knowledge (practical and theoretical) that they can work on. Though I am big believer in focusing on people's strengths being a good programmer requires (I think) being challenged by concepts and ideas that don't always come naturally. We work largely in the web app space using PHP & MySQL but better skills in data modelling, query optimisation, use of MVC and OOP etc. would help the team and the company a lot. I want to help the Dev team manage their careers, explore and expand their skills sets. Be all they can be and better than they were previously. I know its an idealistic goal but work must be about more than simply getting the work done. There should be some time to review, to learn, to grow and get better. Any thoughts, ideas, opinions and directions to tests or similar resources would be greatly appreciated.

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  • Code bacteria: evolving mathematical behavior

    - by Stefano Borini
    It would not be my intention to put a link on my blog, but I don't have any other method to clarify what I really mean. The article is quite long, and it's in three parts (1,2,3), but if you are curious, it's worth the reading. A long time ago (5 years, at least) I programmed a python program which generated "mathematical bacteria". These bacteria are python objects with a simple opcode-based genetic code. You can feed them with a number and they return a number, according to the execution of their code. I generate their genetic codes at random, and apply an environmental selection to those objects producing a result similar to a predefined expected value. Then I let them duplicate, introduce mutations, and evolve them. The result is quite interesting, as their genetic code basically learns how to solve simple equations, even for values different for the training dataset. Now, this thing is just a toy. I had time to waste and I wanted to satisfy my curiosity. however, I assume that something, in terms of research, has been made... I am reinventing the wheel here, I hope. Are you aware of more serious attempts at creating in-silico bacteria like the one I programmed? Please note that this is not really "genetic algorithms". Genetic algorithms is when you use evolution/selection to improve a vector of parameters against a given scoring function. This is kind of different. I optimize the code, not the parameters, against a given scoring function.

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