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• What is the standard way to parse floats at runtime in C?

  - by Joel J. Adamson

  Hello, I have a scientific application for which I want to input initial values at runtime. I have an option to get them from the command line, or to get them from an input file. Either of these options are input to a generic parser that uses strtod to return a linked list of initial values for each simulation run. I either use the command-line argument or getline() to read the values. The question is, should I be rolling my own parser, or should I be using a parser-generator or some library? What is the standard method? This is the only data I will read at runtime, and everything else is set at compile time (except for output files and a few other totally simple things). Thanks, Joel

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• Embarrassingly parallel workflow creates too many output files

  - by Hooked

  On a Linux cluster I run many (N > 10^6) independent computations. Each computation takes only a few minutes and the output is a handful of lines. When N was small I was able to store each result in a separate file to be parsed later. With large N however, I find that I am wasting storage space (for the file creation) and simple commands like ls require extra care due to internal limits of bash: -bash: /bin/ls: Argument list too long. Each computation is required to run through a qsub scheduling algorithm so I am unable to create a master program which simply aggregates the output data to a single file. The simple solution of appending to a single fails when two programs finish at the same time and interleave their output. I have no admin access to the cluster, so installing a system-wide database is not an option. How can I collate the output data from embarrassingly parallel computation before it gets unmanageable?

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• How to access a structure member in a function that get it as void* type?

  - by Ahmad

  I want to have a function that accepts different type of structures as argument. So, since I don't have a specific type, I have to use void*. Now question is: when I pass a structure to this function, how can I access a known member of this structure inside the function? Specifically, I know that all structures have str1 as a member and I want, for example, print it. Here is a sample code: struct { char* str1; float tt1; } var1 = {"This is me", 12}; struct { char* str1; int tt2; } var2 = {"This is you", 18}; void printStruct(void* str) { printf("\n the structure string is %s", ??); //can I put something in ?? to print the string? } main(....) { printStruct(&var1); printStruct(&var2); }

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• Strange error: cannot convert from 'int' to 'ios_base::openmode'

  - by Dylan Klomparens

  I am using g++ to compile some code. I wrote the following snippet: bool WriteAccess = true; string Name = "my_file.txt"; ofstream File; ios_base::open_mode Mode = std::ios_base::in | std::ios_base::binary; if(WriteAccess) Mode |= std::ios_base::out | std::ios_base::trunc; File.open(Name.data(), Mode); And I receive these errors... any idea why? Error 1: invalid conversion from ‘int’ to ‘std::_Ios_Openmode’ Error 2: initializing argument 2 of ‘std::basic_filebuf<_CharT, _Traits* std::basic_filebuf<_CharT, _Traits::open(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits]’ As far as I could tell from a Google search, g++ is actually breaking the C++ standard here. Which I find quite astonishing, since they generally conform very strictly to the standard. Is this the case? Or am I doing something wrong. My reference for the standard: http://www.cplusplus.com/reference/iostream/ofstream/open/

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• How can I make a multi search SPROC/UDF by passing a tabled-value to it?

  - by Shimmy

  I actually want to achieve the following description This is the table argument I want to pass to the server <items> <item category="cats">1</item> <item category="dogs">2</item> </items> SELECT * FROM Item WHERE Item.Category = <one of the items in the XML list> AND Item.ReferenceId = <the corresponding value of that item xml element> --Or in other words: SELECT FROM Items WHERE Item IN XML according to the splecified columns. Am I clear enought? I don't mind to do it in a different way other than xml. What I need is selecting values that mach an array of two of its columns' values.

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• Working with EnumSet class in GWT

  - by zenmonkey

  I am having trouble using EnumSet on the client side. I get this runtime error message: java.util.EnumSet.EnumSetImpl is not default instantiable (it must have a zero-argument constructor or no constructors at all) and has no custom serializer. Is this is a known issue? Here is what I am doing (basically a hello world app) Service: String echo (EnumSet<Names> name) throws IllegalArgumentException; Client: echoServ.echo (EnumSet.of(Names.JOHN), new AsyncCallback<String>() { ....... }); Shared enum class enum Names { JOHN, NUMAN, OBAMA }

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• Bash script function return value problem

  - by Eedoh

  Hi to all. Can anyone help me return the correct value from a bash script function? Here's my function that should return first (and only) line of the file passed as an argument: LOG_FILE_CREATION_TIME() { return_value=`awk 'NR==1' $1` return return_value } And here's my call of that function in the other script: LOG_FILE_CREATION_TIME "logfile" timestamp=$? echo "Timestamp = $timestamp" I always get some random values with this code. If, for example, there's a value of 62772031 in the "logfile", I get Timestamp = 255 as an output. For some other values in the file, I get other random values as a return value, never the correct one. Any ideas?

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• How do I send a file as an email attachment using Linux command line?

  - by Kit Roed

  I've created a script that runs every night on my Linux server that uses mysqldump to back up each of my MySQL databases to .sql files and packages them together as a compressed .tar file. The next step I want to accomplish is to send that tar file through email to a remote email server for safekeeping. I've been able to send the raw script in the body an email by piping the backup text file to mailx like so: $ cat mysqldbbackup.sql | mailx [email protected] cat echoes the backup file's text which is piped into the mailx program with the recipient's email address passed as an argument. While this accomplishes what I need, I think it could be one step better, Is there any way, using shell scripts or otherwise, to send the compressed .tar file to an outgoing email message as an attachment? This would beat having to deal with very long email messages which contain header data and often have word-wrapping issues etc.

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• How do you move the pointer up or down multiple lines with Emacs?

  - by Peter

  I can move my pointer up and down one line with my arrow key just fine in Emacs, so I'd like to redefine C-n and C-p to move up and down 5 lines at a time. I'm just beginning to learn how to use Emacs, and elisp is very alien to me. I tried using the GNU Emacs lisp reference, but I couldn't find how to bind a keystroke to multiple commands. Here's what I have so far (concentrating on the moving up definition): (global-set-key "\C-p" '(loop for i in '(1 2 3 4 5) do ('previous-line))) But, this brings up an error message when I hit C-p, "Wrong type argument." Any suggestions? Thanks!

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• Using a ref Parameter with the this Keyword?

  - by grefly

  Is there a way to force the this keyword to act as a ref argument? I would like to pass in a visitor that modifies multiple properties on the object, but this only wants to act like a value parameter. Code in Object: public void Accept(Visitor<MyObject> visitor) { visitor.Visit(this); } Code in Visitor: public void Visit(ref Visitor<MyObject> receiver) { receiver.Property = new PropertyValue(); receiver.Property2 = new PropertyValue(); }

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• C#: Preferred pattern for functions requiring arguments that implement two interfaces

  - by JS Bangs

  The argument to my function f() must implement two different interfaces that are not related to each other by inheritance, IFoo and IBar. I know of two different ways of doing this. The first is to declare an empty interface that inherits from both: public interface IFooBar : IFoo, IBar { // nothing to see here } public int f(IFooBar arg) { // etc. } This, of course, requires that the classes declare themselves as implementing IFooBar rather than IFoo and IBar separately. The second way is to make f() generic with a constraint: public int f<T>(T arg) where T : IFoo, IBar { // etc. } Which of these do you prefer, and why? Are there any non-obvious advantages or disadvantages to each?

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• Qt compilation and stylesheet

  - by Yosko

  Each time I compile my Qt project after modifying my qss stylesheet file, the modifications aren't taken into account, unless I rebuild everything. Any idea on a workaround for this, so that I don't have to wait 5 minutes each time I change my qss ? Notes: I use Qt 4.8, and my stylsheet is declared in a resource file (qrc). EDIT: As suggested by Luca Carlon, when a qss is reference in the project through a .qrc file, the changes in the qss don't affect the qrc, and the compiler ignores it. To avoid that, I added a Custom Build Step to my project: before the qmake step! calls a .bat file without any argument the .bat contains the real command copy /b files.qrc +,,

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• Advantage Data Architect doesn't accept 'output to', are there any other options for outputting a ta

  - by likesalmon

  I'm trying to output the results of a SELECT query to a tab delimited text file in Advantage Data Architect. I know I can use the 'Export to' feature to do this, but there are a lot of tables and that is going to take forever. I would rather use the SQL editor, but I found out it does not accept the OUTPUT TO argument, even though that command is part of Sybase SQL. I would like to do this: SELECT * FROM tablename; OUTPUT TO 'C:/ExportDirectory' DELIMITED BY '\t' FORMAT TEXT; Is there another way?

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• Best Dijkstra papers to explain this quote?

  - by jemfinch

  I was enjoying "The Humble Programmer" earlier today and ran across this choice quote: Therefore, for the time being and perhaps forever, the rules of the second kind present themselves as elements of discipline required from the programmer. Some of the rules I have in mind are so clear that they can be taught and that there never needs to be an argument as to whether a given program violates them or not. Examples are the requirements that no loop should be written down without providing a proof for termination nor without stating the relation whose invariance will not be destroyed by the execution of the repeatable statement. I'm looking for which of Dijkstra's 1300+ writings best describe in further detail rules such as he was describing above.

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• Can PHP Perform Magic Instantiation?

  - by Aiden Bell

  Despite PHP being a pretty poor language and ad-hoc set of libraries ... of which the mix of functions and objects, random argument orders and generally ill-thought out semantics mean constant WTF moments.... ... I will admit, it is quite fun to program in and is fairly ubiquitous. (waiting for Server-side JavaScript to flesh out though) question: Given a class class RandomName extends CommonAppBase {} is there any way to automatically create an instance of any class extending CommonAppBase without explicitly using new? As a rule there will only be one class definition per PHP file. And appending new RandomName() to the end of all files is something I would like to eliminate. The extending class has no constructor; only CommonAppBase's constructor is called. Strange question, but would be nice if anyone knows a solution. Thanks in advance, Aiden (btw, my PHP version is 5.3.2) Please state version restrictions with any answer.

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• LBA48 in Linux SCSI ATA Passthrough

  - by Ben Englert

  I am writing a custom disk monitoring/diagnostics app which, among other things, needs to do stuff to SATA disks behind a SAS PCI card under Linux. So far I am following this guide as well as the example code in sg_utils to pass ATA taskfiles through the SCSI layer. Seems to be working okay. However, in both cases, the CDB data structure (pointed to by the cmdp member of the sg_io argument to the ioctl) has only one unsigned char worth of space for the number of sectors. If you look at the ata_taskfile structure in linux\ata.h you'll see that it has an "nsect" and a "hob_nsect" field - high order bits for the sector count, to support LBA48. It turns out that in my application I need LBA48 support. So, anyone know how to set up an sg_io_hdr structure with an LBA48 sector count?

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• jQuery Tablesorter - disabled headers show progress bar, sortEnd never triggered

  - by McGirl

  I'm combining Tablesorter's 'disable headers using options' function and the 'trigger sortStart / sortEnd' function and have run into an issue. The following code works fine for the most part, BUT: when you click on a disabled header, the progress-indicating #overlay div appears and never goes away. <script type="text/javascript" id="js"> $(document).ready(function() { // call the tablesorter plugin, the magic happens in the markup $("#projectTable").tablesorter({ // pass the headers argument and assing a object headers: { // assign the secound column (we start counting zero) 1: { // disable it by setting the property sorter to false sorter: false }, // assign the third column (we start counting zero) 2: { // disable it by setting the property sorter to false sorter: false } } }); //assign the sortStart event $("#projectTable").bind("sortStart",function() { $("#overlay").show(); }).bind("sortEnd",function() { $("#overlay").hide(); }); }); </script> Any ideas on how I could fix this so that nothing at all happens when the disabled headers are clicked? Thanks!

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• Beginner Java Question about Integer.parseInt() and casting

  - by happysoul

  so when casting like in the statement below :- int randomNumber=(int) (Math.random()*5) it causes the random no. generated to get converted into an int.. Also there's this method I just came across Integer.parseInt() which does the same ! i.e return an integer Why two different ways to make a value an int ? Also I made a search and it says parseInt() takes string as an argument.. So does this mean that parseInt() is ONLY to convert String into integer ? What about this casting then (int) ?? Can we use this to convert a string to an int too ? sorry if it sounds like a dumb question..I am just confused and trying to understand Help ?

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• shell scripting: nested subshell ++

  - by jhon

  Hi guys, more than a problem, this is a request for "another way to do this" actually, if a want to use the result from a previous command I into another one, I use: R1=$("cat somefile | awk '{ print $1 }'" ) myScript -c $R1 -h123 then, a "better way"is: myScript -c $("cat somefile | awk '{ print $1 }'" ) -h123 but, what if I have to use several times the result, let's say: using several times $R1, well the 2 options: option 1 R1=$("cat somefile | awk '{ print $1}'") myScript -c $R1 -h123 -x$R1 option 2 myScript -c $("cat somefile | awk '{ print $1 }'" ) -h123 -x $("cat somefile | awk '{ print $1 }'" ) do you know another way to "store" the result of a previous command/script and use it as a argument into another command/script? thanks

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• Force line-buffering of stdout when piping to tee

  - by houbysoft

  Usually, stdout is line-buffered. In other words, as long as your printf argument ends with a newline, you can expect the line to be printed instantly. This does not appear to hold when using a pipe to redirect to tee. I have a C++ program, a, that outputs strings, always \n-terminated, to stdout. When it is run by itself (./a), everything prints correctly and at the right time, as expected. However, if I pipe it to tee (./a | tee output.txt), it doesn't print anything until it quits, which defeats the purpose of using tee. I know that I could fix it by adding a fflush(stdout) after each printing operation in the C++ program. But is there a cleaner, easier way? Is there a command I can run, for example, that would force stdout to be line-buffered, even when using a pipe?

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• C++ Passing `this` into method by reference

  - by David

  I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist. This is the header declaration of the constructor: class MixerLine { private: MIXERLINE _mixerLine; public: MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); ~MixerLine(); } This is the code that calls the constructor (MixerDevice.cpp): void MixerDevice::enumerateLines() { DWORD numLines = getDestinationCount(); for(DWORD i=0;i<numLines;i++) { MixerLine mixerLine( this, i ); // other code here removed } } Compilation of MixerDevice.cpp fails with this error: Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &' But I thought pointer values could be assigned to pointers, e.g. Foo* foo = new Foo(); Foo& bar = foo;

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• Python: Hack to call a method on an object that isn't of its class

  - by cool-RR

  Assume you define a class, which has a method which does some complicated processing: class A(object): def my_method(self): # Some complicated processing is done here return self And now you want to use that method on some object from another class entirely. Like, you want to do A.my_method(7). This is what you'd get: TypeError: unbound method my_method() must be called with A instance as first argument (got int instance instead). Now, is there any possibility to hack things so you could call that method on 7? I'd want to avoid moving the function or rewriting it. (Note that the method's logic does depend on self.) One note: I know that some people will want to say, "You're doing it wrong! You're abusing Python! You shouldn't do it!" So yes, I know, this is a terrible terrible thing I want to do. I'm asking if someone knows how to do it, not how to preach to me that I shouldn't do it.

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• R: simple and short if clauses for combind statements

  - by jorgusch

  Hello, TRUE/FALSE if clauses are easily and quickly done in R. However, if the argument gets more complex, it also gets ugly very soon. For instance: I might want to execute different operations for a row(foo) dependent on the value in one cell (foo[1]). Let the intervals be 0:39 and 40:59 and 60:100 Something like does not exit: (if foo[1] "in" 40:60){... In fact, I only see ways of at least two if clauses and two else statements and the action for the first interval somewhere at the bottom of the code. With more intervals(or any other condition) it is getting more complex. Is there a best practice (for this purpose or others) with a simple construction and nice design to read? Thanks a lot!

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• Using __str__ representation for printing objects in containers in Python

  - by BobDobbs

  I've noticed that when an instance with an overloaded str method is passed to the print() function as an argument, it prints as intended. However, when passing a container that contains one of those instances to print(), it uses the repr method instead. That is to say, print(x) displays the correct string representation of x, and print(x, y) works correctly, but print([x]) or print((x, y)) prints the repr representation instead. First off, why does this happen? Secondly, is there a way to correct that behavior of print() in this circumstance?

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