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  • Supporting Piping (A Useful Hello World)

    - by blastthisinferno
    I am trying to write a collection of simple C++ programs that follow the basic Unix philosophy by: Make each program do one thing well. Expect the output of every program to become the input to another, as yet unknown, program. I'm having an issue trying to get the output of one to be the input of the other, and getting the output of one be the input of a separate instance of itself. Very briefly, I have a program add which takes arguments and spits out the summation. I want to be able to pipe the output to another add instance. ./add 1 2 | ./add 3 4 That should yield 6 but currently yields 10. I've encountered two problems: The cin waits for user input from the console. I don't want this, and haven't been able to find a simple example showing a the use of standard input stream without querying the user in the console. If someone knows of an example please let me know. I can't figure out how to use standard input while supporting piping. Currently, it appears it does not work. If I issue the command ./add 1 2 | ./add 3 4 it results in 7. The relevant code is below: add.cpp snippet // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing if (numbers.size() > 0) { double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } std::cout << sum << std::endl; } else { double input; // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> input; std::cout << input << std::endl; } } // ... MORE IRRELEVANT CODE ... So, I guess my question(s) is does anyone see what is incorrect with this code in order to support piping standard input? Are there some well known (or hidden) resources that explain clearly how to implement an example application supporting the basic Unix philosophy? @Chris Lutz I've changed the code to what's below. The problem where cin still waits for user input on the console, and doesn't just take from the standard input passed from the pipe. Am I missing something trivial for handling this? I haven't tried Greg Hewgill's answer yet, but don't see how that would help since the issue is still with cin. // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> arg; std::cout << arg << std::endl; } std::cout << sum << std::endl; // ... MORE IRRELEVANT CODE ...

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  • what is the programmatic parlance for this phenomenon?

    - by deostroll
    Here is javascript code (jquery) for adding a row of images: var tr = $('<tr>'); var td = '<td><img src="myimg.jpg"/></td>'; tr.append(td).append(td).append(td); $('#mytable tbody tr:eq(0)').before(tr); tr.empty(); //I really don't need this line... Technically tr.empty() shouldn't have worked. It actually does the opposite of what I want. What is the techinical term for this behaviour - You've added tr to the DOM, but any jquery function calls to that object still works, where as you'd normally not expect it to work i.e. make changes to the DOM?

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  • How to initialize F# list when size is unknown, using while..do loop

    - by James Black
    I have a function that will parse the results of a DataReader, and I don't know how many items are returned, so I want to use a while..do loop to iterate over the reader, and the outcome should be a list of a certain type. (fun(reader) -> [ while reader.Read() do new CityType(Id=(reader.GetInt32 0), Name=(reader.GetString 1), StateName=(reader.GetString 2)) ]) This is what I tried, but the warning I get is: This expression should have type 'unit', but has type 'CityType'. Use 'ignore' to discard the result of the expression, or 'let' to bind the result to a name. So what is the best way to iterate over a DataReader and create a list?

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  • How to automatically run in the background?

    - by Hun1Ahpu
    I'm not sure that it's not implemented yet, I hope that it is. But I know that in .Net programmers should manually run time-consuming task in the background thread. So every time we handle some UI event and we understand that this will take some time we also understand that this will hang UI thread and our application. And then we make all this Background work things and handle callbacks or whatever. So my question is: Is there in some language/platform a mechanism that will automatically run time-consuming tasks in the background and will do all related work itself? So we just write the code for handling specific UI event and this code will be somehow detected as time-consuming and will be executed in background. And if there isn't, then why?

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  • Sparse linear program solver

    - by Jacob
    This great SO answer points to a good sparse solver, but I've got constraints on x (for Ax = b) such that each element in x is >=0 an <=N. The first thing which comes to mind is an LP solver for large sparse matrices. Any ideas/recommendations?

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • In what specific areas has F# proven more applicable than C#?

    - by Peter McGrattan
    Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#. EDIT: Altered title with the intent of reducing perceived ambiguity.

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  • How can I pass methods in javascript?

    - by peterjwest
    I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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  • C++ String manipulation isn't making sense to me...

    - by Andrew Bolster
    I am trying some of the Stanford SEE courses online to learn some new languages; this particular assignment has to do with removing substrings from strings. What I've got so far is below, but if text = "hello hello" and remove ="el", it gets stuck in a loop, but if i change text to text = "hello hllo", it works, making me think I'm doing something obviously stupid. There is a stipulation in the assignment not to modify the incoming strings, and instead to return a new string. string CensorString1(string text, string remove){ string returned; size_t found=0, lastfound=0; found = (text.substr(lastfound,text.size())).find(remove); while (string::npos != found ){ returned += text.substr(lastfound,found); lastfound = found + remove.size(); found = (text.substr(lastfound,text.size())).find(remove); } returned += text.substr(lastfound,found); return returned; } Guidance would be appreciated :-) Thanks

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  • Using Cases to change background colour | Visual Studio 2008

    - by Simon
    I really need help working with cases, I'm only learning it so far, but just can't get a drop down menu to work that would change the background of a Textbox. Private Sub cbColours_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cbColours.SelectedIndexChanged Select Case colours Case Is = "Red" txtSpace.BackColor = Color.Red Case Is = "Blue" txtSpace.BackColor = Color.Blue Case Is = "Green" txtSpace.BackColor = Color.Green End Select End Sub It isn't doing anything at all... In the dropdown menu, it has Red, Blue and Green one per line When the value (e.g. Green) is clicked, it will then change the Textbox to the colour selected. Many help appreciated :)

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  • What language is this???

    - by Misha Koshelev
    Dear All: I thought this was Javascript... but parser is giving me trouble. Any ideas? Thank you! Misha for (;;); {"error":0,"errorSummary":"","errorDescription":"","errorIsWarning":false,"silentError":0,"payload":{"collections": [{"name":"bcm","type":"flp","filter":"flp_662923563701","value":"662923563701","editable":true,"deletable":true,"members": ["1319651388","539562714","710814793","569071038","1553739575","2413243"]}, {"name":"mstp","type":"flp","filter":"flp_715806870131","value":"715806870131","editable":true,"deletable":true,"members": ["1263807225","1159429816","508447486","508005223","1234906348","642723993","552875889","23401888","10701320","8302901","7931988","3007490","1286522890","1128447272","1076062553","775679867","737520202","640799498","224400055","224400048","14211567","7909445","3005965","2404364","218216","660037273","224400089","73306230","9603033","1111694","1034418884","775680513" ,"704526828","518753881","512477182","224400016","24904610","19000876","5403952","3005641","2100348","100000421128298","1445411167","691445174","1020020100","795471177","683724539","682441089","532450522","224400129","224400005","3006522","2246813","1302265","7197","1900494", "100000474978266","2533582","1205125","1384091677","1260996959","710814793","514951289","224400164","224400156","173601800","13304723","7938844","3004783","3001379","302817","716739950 ","706849","1418109424","562676898","82501644","3007569","13173"]}, {"name":"mystery","type":"flp","filter":"flp_687949656211","value":"687949656211","editable":true,"deletable":true,"members": ["100001286464748","508123007","100001161894460","1148567030","1048974191","769992391","831734347","15347","1297180076","756692945","3005266","733396195","34410910","100000940154241"," 748426280","569417581","1318922027","100000164920046","1475269609","1436536592","10000016210 8385","754095305","100000421128298","537833189","100000692471928","7920231","673753496","3006217","1221878","8365333","1128447272","224400133","218216","505457123","1421958541","183829 5926","2349408","1622810085","1201640391","510959992","23429895","542118016","1017385668","586225579","625100539","100000474886633","26404148","1384091677","224400156","806908635","843 187401","400435","768261176","7901808","748496482","1541469473","2511982","25401573","503715 506","1226000844","559195162","41400094","1099436201","409816","1584400985","1577092523","100000349351880","199301581"]},{"name":"SMS Subscriptions","type":"ms","filter":"ms","value":"3","editable":true,"deletable":false,"members":[]}],"current_view":false}}

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  • What are these lines doing?

    - by Montecristo
    I'm starting learning javascript for a project, I've found a script that does a part of what I need to do, I'd like to know how it works, both for me and in case it needs to be modified. Originally it was used inside the page, now I've put it in a file on its own and does not work anymore, so I'm dividing it in parts, because I fail to get the whole thing. Here is what bother me most for now: 1) Is this a declaration a function? What is its name? How can it be invoked? (function() { //some code })(); 2) No clue of what is going on here var VARIABLE = VARIABLE || {}; 3) Am I defining a the implementation of methodCall here? Something like overriding a method in Java? VARIABLE.methodCall = function(parameter) { console.log("parameter was: " + parameter); }; Thank you in advance for your help.

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  • What is your company's stance on Developers using Laptops?

    - by codepunk
    I am a developer and my company is moving towards a "no laptop" policy in fear of them being lost or stolen and source code being compromised. Now I don't work for NASA, the military or anything labeled Top Secret but our code is very important to our business nonetheless (as all source code would be). I'll be honest, I disagree with this policy against laptops and wanted to see what others think. I'd like to know: What is your team/company's stance on laptops Your company's size and/or field (small, medium or large, Fortune 500, etc). Whether you've had to take any extra precautions (signing any additional legal, ensure your hard drive is encrypted, etc). Thanks!

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  • socket timeout and remove O_NONBLOCK option

    - by juxstapose
    Hello, I implemented a socket timeout and retry but in order to do it I had to set the socket as a non-blocking socket. However, I need the socket to block. This was my attempt at a solution to these two problems. This is not working. Subsequent send calls block but never send any data. When I connect without the select and the timeout, subsequent send calls work normally. References: C: socket connection timeout How to reset a socket back to blocking mode (after I set it to nonblocking mode)? Code: fd_set fdset; struct timeval tv; fcntl(dsock, F_SETFL, O_NONBLOCK); tv.tv_sec = theDeviceTimeout; tv.tv_usec = 0; int retries=0; logi(theLogOutput, LOG_INFO, "connecting to device socket num retrys: %i", theDeviceRetry); for(retries=0;retries<theDeviceRetry;retries++) { connect(dsock, (struct sockaddr *)&daddr, sizeof daddr); FD_ZERO(&fdset); FD_SET(dsock, &fdset); if (select(dsock + 1, NULL, &fdset, NULL, &tv) == 1) { int so_error; socklen_t slen = sizeof so_error; getsockopt(dsock, SOL_SOCKET, SO_ERROR, &so_error, &slen); if (so_error == 0) { logi(theLogOutput, LOG_INFO, "connected to socket on port %i on %s", theDevicePort, theDeviceIP); break; } else { logi(theLogOutput, LOG_WARN, "connect to %i failed on ip %s because %s retries %i", theDevicePort, theDeviceIP, strerror(errno), retries); logi(theLogOutput, LOG_WARN, "failed to connect to device %s", strerror(errno)); logi(theLogOutput, LOG_WARN, "error: %i %s", so_error, strerror(so_error)); continue; } } } int opts; opts = fcntl(dsock,F_GETFL); logi(theLogOutput, LOG_DEBUG, "clearing nonblock option %i retries %i", opts, retries); opts ^= O_NONBLOCK; fcntl(dsock, F_SETFL, opts);

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  • Problem with .release behavior in file_operations

    - by Yannick
    Hello, I'm dealing with a problem in a kernel module that get data from userspace using a /proc entry. I set open/write/release entries for my own defined /proc entry, and manage well to use it to get data from userspace. I handle errors in open/write functions well, and they are visible to user as open/fopen or write/fwrite/fprintf errors. But some of the errors can only be checked at close (because it's the time all the data is available). In these cases I return something different than 0, which I supposed to be in some way the value 'close' or 'fclose' will return to user. But whatever the value I return my close behave like if all is fine. To be sure I replaced all the release() code by a simple 'return(-1);' and wrote a program that open/write/close the /proc entry, and prints the close return value (and the errno). It always return '0' whatever the value I give. Behavior is the same with 'fclose', or by using shell mechanism (echo "..." /proc/my/entry). Any clue about this strange behavior that is not the one claimed in many tutorials I found? BTW I'm using RHEL5 kernel (2.6.18, redhat modified), on a 64bit system. Thanks. Regards, Yannick

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  • Why isn't LISP more widely used?

    - by Chris
    I've heard a lot of people espouse the capabilities of LISP and its omnipotent macros. If LISP is such a great language, why isn't it being adopted more? What problems is LISP facing that is holding it back from (re)emerging as popular language? Is it something about LISP itself ("those brackets!" isn't the answer, is it?!), or its competitors (e.g. the dominance of Java, .NET)?

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  • how to create http headers from scratch

    - by Sean Ochoa
    So, I made a simple socket server using python. And now I'm trying to structure a proper http response. However, I can't seem to find any sort of tutorial or spec that discusses how to format http responses. Could someone point me to the right place?

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  • Template function as a template argument

    - by Kos
    I've just got confused how to implement something in a generic way in C++. It's a bit convoluted, so let me explain step by step. Consider such code: void a(int) { // do something } void b(int) { // something else } void function1() { a(123); a(456); } void function2() { b(123); b(456); } void test() { function1(); function2(); } It's easily noticable that function1 and function2 do the same, with the only different part being the internal function. Therefore, I want to make function generic to avoid code redundancy. I can do it using function pointers or templates. Let me choose the latter for now. My thinking is that it's better since the compiler will surely be able to inline the functions - am I correct? Can compilers still inline the calls if they are made via function pointers? This is a side-question. OK, back to the original point... A solution with templates: void a(int) { // do something } void b(int) { // something else } template<void (*param)(int) > void function() { param(123); param(456); } void test() { function<a>(); function<b>(); } All OK. But I'm running into a problem: Can I still do that if a and b are generics themselves? template<typename T> void a(T t) { // do something } template<typename T> void b(T t) { // something else } template< ...param... > // ??? void function() { param<SomeType>(someobj); param<AnotherType>(someotherobj); } void test() { function<a>(); function<b>(); } I know that a template parameter can be one of: a type, a template type, a value of a type. None of those seems to cover my situation. My main question is hence: How do I solve that, i.e. define function() in the last example? (Yes, function pointers seem to be a workaround in this exact case - provided they can also be inlined - but I'm looking for a general solution for this class of problems).

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  • Prolog: using the sort/2 predicate

    - by Øyvind Hauge
    So I'm trying to get rid of the wrapper clause by using the sort library predicate directly inside split. What split does is just generating a list of numbers from a list that looks like this: [1:2,3:2,4:6] ---split-- [1,2,3,2,4,6]. But the generated list contains duplicates, and I don't want that, so I'm using the wrapper to combine split and sort, which then generates the desired result: [1,2,3,4,6]. I'd really like to get rid of the wrapper and just use sort within split, however I keep getting "ERROR: sort/2: Arguments are not sufficiently instantiated." Any ideas? Thanks :) split([],[]). split([H1:H2|T],[H1,H2|NT]) :- split(T,NT). wrapper(L,Processed) :- split(L,L2), sort(L2,Processed).

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  • What coding standards do you follow?

    - by Mark Szymanski
    I was just curious what coding standards people followed. I for one use the following: Brackets ALWAYS go on the next line. For instance: int main() { //Blah... } I never use code folding. (Yes my IDE's do support it (Xcode and Eclipse). Put related functions/methods single-spaced, otherwise double space. Here is an example: int foo = 0; printf("%d",foo); those are related while these are not: printf("Hello, World!"); return(0); I don't put else statements on the same line as the closing bracket for the preceding if statement. Most of the time in Java if a program needs multiple try catch statements I will just put the whole thing in one try catch.

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