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  • C++ Constructor Initializer List - using member functions of initialized members

    - by Andy
    I've run into the following a few times with initializer lists and I've never been able to explain it well. Can anyone explain why exactly the following fails (I don't have a compiler to catch typos, so bear with me): class Foo { public: Foo( int i ) : m_i( i ) {} //works with no problem int getInt() {return m_i;} ~Foo {} private: int m_i; }; class Bar { public: Bar() : m_foo( 5 ), //this is ok m_myInt( m_foo.getInt() ) //runtime error, seg 11 {} ~Bar() {} private: Foo m_foo; int m_myInt; }; When trying to call member functions of members initialized higher up the initializer list, I get seg faults. I seem to recall this is a known problem (or perhaps somehow by design) but I've never seen it well described. The attached example is contrived with plain old data types, but substitute the Bar::m_myInt with another object lacking a default (empty) constructor and the issue is more real. Can anyone enlighten me? Thanks!

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  • Best Practice: Access form elements by HTML id or name attribute?

    - by seth
    As any seasoned JavaScript developer knows, there are many (too many) ways to do the same thing. For example, say you have a text field as follows: <form name="myForm"> <input type="text" name="foo" id="foo" /> There are many way to access this in JavaScript: [1] document.forms[0].elements[0]; [2] document.myForm.foo; [3] document.getElementById('foo'); [4] document.getElementById('myForm').foo; ... and so on ... Methods [1] and [3] are well documented in the Mozilla Gecko documentation, but neither are ideal. [1] is just too general to be useful and [3] requires both an id and a name (assuming you will be posting the data to a server side language). Ideally, it would be best to have only an id attribute or a name attribute (having both is somewhat redundant, especially if the id isn't necessary for any css, and increases the likelihood of typos, etc). [2] seems to be the most intuitive and it seems to be widely used, but I haven't seen it referenced in the Gecko documentation and I'm worried about both forwards compatibility and cross browser compatiblity (and of course I want to be as standards compliant as possible). So what's best practice here? Can anyone point to something in the DOM documentation or W3C specification that could resolve this? Note I am specifically interested in a non-library solution (jQuery/Prototype).

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  • C pointer array scope and function calls

    - by juvenis
    I have this situation: { float foo[10]; for (int i = 0; i < 10; i++) { foo[i] = 1.0f; } object.function1(foo); // stores the float pointer to a const void* member of object } object.function2(); // uses the stored void pointer Are the contents of the float pointer unknown in the second function call? It seems that I get weird results when I run my program. But if I declare the float foo[10] to be const and initialize it in the declaration, I get correct results. Why is this happening?

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  • Making the #include square

    - by David
    I'm trying to write a makefile using CC on Solaris 10. [Only the first bit of that really matters, I think]. I have the following rule for foo.o: foo.o: foo.cc common_dependencies.h CC -c foo.cc -I../../common Unfortunately, common_dependencies.h includes all sorts of idiosyncratic trash, in directories not named '.' or '../../common' . Is this just going to have to be a brute force makefile where I ferret out all of the dependency paths? All of the dependencies are somewhere under '../..', but sometimes 1-level down and sometimes 2-levels down.

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  • Help needed to convert code from C# to Python.

    - by Ali
    Can you please convert this code from C# to Python to be run on IronPython? I don’t have any experience with Python. using System; using Baz; namespace ConsoleApplication { class Program { static void Main() { Portal foo = new Portal("Foo"); Agent bar = new Agent("Bar"); foo.Connect("127.0.0.1", 1234); foo.Add(bar); bar.Ready += new Agent.ReadyHandler(bar_Ready); } static void bar_Ready(object sender, string msg) { Console.WriteLine(msg.body); } } }

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  • LINQ to Entites: How should I handle System.InvalidOperationException when checking for existance of

    - by chris
    I have a many-to-one relationship that users can edit via checkboxes. PK of Foo is ID, and fid contains the id from the checkbox. I'm checking to see if an element exists with: Foo ent; try { ent = ctx.Foo.First(f => f.ID == fid); } catch (System.InvalidOperationException ioe) { ent = new Foo(); } It seems to me that I should be able to do this without throwing an exception. What would be the best way to do this?

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  • any equivalent to VB.net function name as return value in C#?

    - by user1179861
    In vb.net there is a weird approach that you can use the function name as the result variable.. example: Function Foo(ByVal bar As Integer) As List(Of Integer) Foo = New List(Of Integer) Foo.Add(bar + 1) End Function As far as i know, in C# you have to: List<int> foo(int bar) { var result = new List<int>(); result.Add(bar + 1); return result; } I'm not sure if it's by design or i just don't know the right way to do this.. Please enlight me! Thanks in advance, Eitan.

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  • Javascript Namespace Declaration

    - by objektivs
    What neat ways do you use for declaring JavaScript namespaces. I've come across this one: if (Foo == null || typeof(Foo) != "object") { var Foo = new Object();} Is there a more elegant or succinct way of doing this? Just a bit of fun...

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  • Why is forwarding variadic parameters invalid?

    - by awesomeyi
    Consider the variadic function parameter: func foo(bar:Int...) -> () { } Here foo can accept multiple arguments, eg foo(5,4). I am curious about the type of Int... and its supported operations. For example, why is this invalid? func foo2(bar2:Int...) -> () { foo(bar2); } Gives a error: Could not find an overload for '_conversion' that accepts the supplied arguments Why is forwarding variadic parameters invalid? What is the "conversion" the compiler is complaining about?

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  • How to return a string literal from a function

    - by skydoor
    Hi I am always confused about return a string literal or a string from a function. I was told that there might be memory leak because you don't know when the memory will be deleted? For example, in the code below, how to implement foo() so that make the output of the code is "Hello World"? void foo ( ) // you can add parameters here. { } int main () { char *c; foo ( ); printf ("%s",c); return 0; } Also if the return type of foo() is not void, but you can return char*, what should it be.

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  • Can I create class properties during __new__ or __init__?

    - by 007brendan
    I want to do something like this. The _print_attr function is designed to be called lazily, so I don't want to evaluate it in the init and set the value to attr. I would like to make attr a property that computes _print_attr only when accessed: class Base(object): def __init__(self): for attr in self._edl_uniform_attrs: setattr(self, attr, property(lambda self: self._print_attr(attr))) def _print_attr(self, attr): print attr class Child(Base): _edl_uniform_attrs = ['foo', 'bar'] me = Child() me.foo me.bar #output: #"foo" #"bar"

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  • Are Conditional subquery

    - by Tobias Schulte
    I have a table foo and a table bar, where each foo might have a bar (and a bar might belong to multiple foos). Now I need to select all foos with a bar. My sql looks like this SELECT * FROM foo f WHERE [...] AND ($param IS NULL OR (SELECT ((COUNT(*))>0) FROM bar b WHERE f.bar = b.id)) with $param being replaced at runtime. The question is: Will the subquery be executed even if param is null, or will the dbms optimize the subquery out?

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  • Mapping over multiple Seq in Scala

    - by bsdfish
    Suppose I have val foo : Seq[Double] = ... val bar : Seq[Double] = ... and I wish to produce a seq where the baz(i) = foo(i) + bar(i). One way I can think of to do this is val baz : Seq[Double] = (foo.toList zip bar.toList) map ((f: Double, b : Double) => f+b) However, this feels both ugly and inefficient -- I have to convert both seqs to lists (which explodes with lazy lists), create this temporary list of tuples, only to map over it and let it be GCed. Maybe streams solve the lazy problem, but in any case, this feels like unnecessarily ugly. In lisp, the map function would map over multiple sequences. I would write (mapcar (lambda (f b) (+ f b)) foo bar) And no temporary lists would get created anywhere. Is there a map-over-multiple-lists function in Scala, or is zip combined with destructuring really the 'right' way to do this?

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  • HREF link that targets nothing, does not want to use hash or void(0)

    - by Mattis
    I have a link that I want to be able to click to trigger a piece of jQuery code. Currently I have <a href="#" id="foo">Link</a> and $('#foo').click(function(){ // Do stuff }); which works well. But, I have always hated using hash in this way. The page flickers and the hash is added to the page url. One alternative is to use <a href="javascript:void(0);" id="foo">Link</a> but I also dislike seeing that piece of code in the browser status bar. It looks tacky. What I'd rather have is an explanatory javascript placeholder that does nothing, like <a href="javascript:zoom();" id="foo">Link</a> which actually works, but throws an ReferenceError in the javascript console since there are no such function. What's the minimum definition of a function that does nothing? Are there any other alternatives? Should I just skip the link and use something like <span id="foo" style="cursor:pointer;cursor:hand;">Link</span> instead?

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  • Why is Func<T> ambiguous with Func<IEnumerable<T>>?

    - by Matt Hamilton
    This one's got me flummoxed, so I thought I'd ask here in the hope that a C# guru can explain it to me. Why does this code generate an error? class Program { static void Main(string[] args) { Foo(X); // the error is on this line } static String X() { return "Test"; } static void Foo(Func<IEnumerable<String>> x) { } static void Foo(Func<String> x) { } } The error in question: Error 1 The call is ambiguous between the following methods or properties: 'ConsoleApplication1.Program.Foo(System.Func<System.Collections.Generic.IEnumerable<string>>)' and 'ConsoleApplication1.Program.Foo(System.Func<string>)' C:\Users\mabster\AppData\Local\Temporary Projects\ConsoleApplication1\Program.cs 12 13 ConsoleApplication1 It doesn't matter what type I use - if you replace the "String" declarations with "int" in that code you'll get the same sort of error. It's like the compiler can't tell the difference between Func<T> and Func<IEnumerable<T>>. Can someone shed some light on this?

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  • How to treat Base* pointer as Derived<T>* pointer?

    - by dehmann
    I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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  • Java: Make a method abstract for each extending class

    - by Martijn Courteaux
    Hi, Is there any keyword or design pattern for doing this? public abstract class Root { public abstract void foo(); } public abstract class SubClass extends Root { public void foo() { // Do something } } public class SubberClass extends SubClass { // Here is it not necessary to override foo() // So is there a way to make this necessary? // A way to obligate the developer make again the override } Thanks

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  • Using JavaScript to change the URL used when a page is bookmarked...

    - by user30997
    JavaScript doesn't allow you to update window.location without triggering a reload. While I agree with this policy in principle (it shouldn't be possible to visit my website and have JavaScript change the location bar to read www.yourbankingsite.com,) I believe that it should be possible to change www.foo.org/index to www.foo.org/help. The only reason I care about this is for bookmarking. I'm working on a photo browser, and when a user is previewing a particular image, I want that image to be the default if they should bookmark that page. For example, if they are viewing foo.org/preview/images0-30 and they click on image #15, that image is expanded to a medium-sized view. If they then bookmark the page, I want the bookmark URL to be foo.org/preview/images0-30/active15. Any thoughts, or is there a security barrier on this one as well? I can certainly understand the same policy being applied here, but one can dream.

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  • detecting object-reference duplication across JavaScript files

    - by AnC
    I have a number of files with contents like this: function hello() { ... element1.text = foo.locale.lorem; element2.text = foo.locale.ipsum; ... elementn.text = foo.locale.whatever; ... } function world() { ... var label = bar.options.baz.blah; var toggle = bar.options.baz.use_toggle; ... } This could be written more efficiently, and also be more readable, by creating a shortcut to the locale object: function hello() { var loc = foo.locale; ... element1.text = loc.lorem; element2.text = loc.ipsum; ... elementn.text = loc.whatever; ... } function world() { var options = bar.options.baz; ... var label = options.blah; var toggle = options.use_toggle; ... } Is there a simple way to detect occurrences of such duplication for any arbitrary object (it's not always as simple as "locale", or foo.something)? Basically, I wanna know where lengthy object references appear two or more times within a function. Thanks!

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  • In what circumstances are instance variables declared as '_var' in 'use fields' readonly?

    - by Pedro Silva
    I'm trying to understand the behavior of the fields pragma, which I find poorly documented, regarding fields prefixed with underscores. This is what the documentation has to say about it: Field names that start with an underscore character are made private to the class and are not visible to subclasses. Inherited fields can be overridden but will generate a warning if used together with the -w switch. This is not consistent with its actual behavior, according to my test, below. Not only are _-prefixed fields visible within a subclass, they are visible within foreign classes as well (unless I don't get what 'visible' means). Also, directly accessing the restricted hash works fine. Where can I find more about the behavior of the fields pragma, short of going at the source code? { package Foo; use strict; use warnings; use fields qw/a _b __c/; sub new { my ( $class ) = @_; my Foo $self = fields::new($class); $self->a = 1; $self->b = 2; $self->c = 3; return $self; } sub a : lvalue { shift->{a} } sub b : lvalue { shift->{_b} } sub c : lvalue { shift->{__c} } } { package Bar; use base 'Foo'; use strict; use warnings; use Data::Dumper; my $o = Bar->new; print Dumper $o; ##$VAR1 = bless({'_b' => 2, '__c' => 3, 'a' => 1}, 'Foo'); $o->a = 4; $o->b = 5; $o->c = 6; print Dumper $o; ##$VAR1 = bless({'_b' => 5, '__c' => 6, 'a' => 4}, 'Foo'); $o->{a} = 7; $o->{_b} = 8; $o->{__c} = 9; print Dumper $o; ##$VAR1 = bless({'_b' => 8, '__c' => 9, 'a' => 7}, 'Foo'); }

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  • Are closures in javascript recompiled

    - by Discodancer
    Let's say we have this code (forget about prototypes for a moment): function A(){ var foo = 1; this.method = function(){ return foo; } } var a = new A(); is the inner function recompiled each time the function A is run? Or is it better (and why) to do it like this: function method = function(){ return this.foo; } function A(){ this.foo = 1; this.method = method; } var a = new A(); Or are the javascript engines smart enough not to create a new 'method' function every time? Specifically Google's v8 and node.js. Also, any general recommendations on when to use which technique are welcome. In my specific example, it really suits me to use the first example, but I know thath the outer function will be instantiated many times.

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  • Optimizing simple search script in PowerShell

    - by cc0
    I need to create a script to search through just below a million files of text, code, etc. to find matches and then output all hits on a particular string pattern to a CSV file. So far I made this; $location = 'C:\Work*' $arr = "foo", "bar" #Where "foo" and "bar" are string patterns I want to search for (separately) for($i=0;$i -lt $arr.length; $i++) { Get-ChildItem $location -recurse | select-string -pattern $($arr[$i]) | select-object Path | Export-Csv "C:\Work\Results\$($arr[$i]).txt" } This returns to me a CSV file named "foo.txt" with a list of all files with the word "foo" in it, and a file named "bar.txt" with a list of all files containing the word "bar". Is there any way anyone can think of to optimize this script to make it work faster? Or ideas on how to make an entirely different, but equivalent script that just works faster? All input appreciated!

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  • Parallelize Bash Script

    - by thelsdj
    Lets say I have a loop in bash: for foo in `some-command` do do-something $foo done do-something is cpu bound and I have a nice shiny 4 core processor. I'd like to be able to run up to 4 do-something's at once. The naive approach seems to be: for foo in `some-command` do do-something $foo & done This will run all do-somethings at once, but there are a couple downsides, mainly that do-something may also have some significant I/O which performing all at once might slow down a bit. The other problem is that this code block returns immediately, so no way to do other work when all the do-somethings are finished. How would you write this loop so there are always X do-somethings running at once?

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  • Python interpreter invocation with "-c" and indentation issues

    - by alexander
    I'm trying to invoke Python using the "-c" argument to allow me to run some arbitrary python code easily, like this: python.exe -c "for idx in range(10): print idx" Now this code works fine, from within my batch file, however, I'm running into problems when I want to do anything more than this. Consider the following Python code: foo = 'bar' for idx in range(10): print idx this would then give you 0-9 on the stdout. However, if I collapse this into a single line, using semicolons as delimiters, to get the following: foo = 'bar';for idx in range(10): print idx and try to run it using python.exe -c it get a SyntaxError raised: C:\Python>python.exe -c "foo = 'bar';for idx in range(10): print idx" File "<string>", line 1 foo = 'bar';for idx in range(10): print idx ^ SyntaxError: invalid syntax Anyone know how I can actually use this without switching to a separate .py file?

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