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  • This code appears to achieve the return of a null reference in C++

    - by Chuck
    Hi folks, My C++ knowledge is somewhat piecemeal. I was reworking some code at work. I changed a function to return a reference to a type. Inside, I look up an object based on an identifier passed in, then return a reference to the object if found. Of course I ran into the issue of what to return if I don't find the object, and in looking around the web, many people claim that returning a "null reference" in C++ is impossible. Based on this advice, I tried the trick of returning a success/fail boolean, and making the object reference an out parameter. However, I ran into the roadblock of needing to initialize the references I would pass as actual parameters, and of course there is no way to do this. I retreated to the usual approach of just returning a pointer. I asked a colleague about it. He uses the following trick quite often, which is accepted by both a recent version of the Sun compiler and by gcc: MyType& someFunc(int id) { // successful case here: // ... // fail case: return *static_cast<MyType*>(0); } // Use: ... MyType& mt = somefunc(myIdNum); if (&mt) // test for "null reference" { // whatever } ... I have been maintaining this code base for a while, but I find that I don't have as much time to look up the small details about the language as I would like. I've been digging through my reference book but the answer to this one eludes me. Now, I had a C++ course a few years ago, and therein we emphasized that in C++ everything is types, so I try to keep that in mind when thinking things through. Deconstructing the expression: "*static_cast(0);", it indeed seems to me that we take a literal zero, cast it to a pointer to MyType (which makes it a null pointer), and then apply the dereferencing operator in the context of assigning to a reference type (the return type), which should give me a reference to the same object pointed to by the pointer. This sure looks like returning a null reference to me. Any advice in explaining why this works (or why it shouldn't) would be greatly appreciated. Thanks, Chuck

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  • Oracle select query

    - by Jasim
    I have a table like this C1 C2 C3 Code 1 2 3 33 1 2 3 34 2 4 1 14 1 2 3 14 i want to select only those record whose code is appearing only in single row. ie, in this case rows with code 33 and 34.. as they appear only once in this table. How can i write a query for that

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  • Python: How to extract xml embedded in a html file?

    - by georgehu
    I have a html file with xml snipped embedded, the source code is pasted in the pastbin: http://pastebin.com/Hy0QaWk8 my task is to extract the text enclosed in the first textarea, which is a xml snippet, from the html. Without any change to the original snippet. I'm able to get it by using the BeautifulSoup, but it changes all the tag names into lower case.

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  • PyGTK: Radiobuttons are still displayed after removal

    - by canavanin
    Hi everyone! I am using PyGTK and the gtk.assistant. On one page I would like to display two radiobuttons in case the user selected a certain option on a previous page. The labels of the buttons - and whether the buttons are to be present at all - are to depend entirely on that earlier selection. Furthermore, if the user goes back and changes that selection, the page containing the radiobuttons is to be updated accordingly. I have got as far as having the radiobuttons displayed when necessary, and with the correct labels. The trouble is that if I go back and change the determining selection, or if I move one page further than the 'radiobutton page' and then move back, the buttons are not only not removed (in case that would have been required), their number has also doubled. To show you what I'm doing, here's part of my code (I've left out bits that do unrelated things, that's why the function name doesn't fit). The function is called when the "prepare" signal is emitted prior to construction of the 'radiobutten page'. def make_class_skills_treestore(self): print self.trained_by_default_hbox.get_children() # PRINT 1 for child in self.trained_by_default_hbox.get_children(): if type(child) == gtk.RadioButton: self.trained_by_default_hbox.remove(child) #child.destroy() # <-- removed the labels, but not the buttons print self.trained_by_default_hbox.get_children() # PRINT 2 class_skills = self.data.data['classes'][selected_class].class_skills.values() default_trained_count = (class_skills.count([True, True]) , class_skills.count([True, False])) num_default_trained_skills = default_trained_count[1] / 2 # you have to pick one of a pair --> don't # count each as trained by default for i in range(default_trained_count[0]): # those are trained by default --> no choice num_default_trained_skills +=1 selected_class = self.get_classes_key_from_class_selection() if default_trained_count[1]: for skill in self.data.data['classes'][selected_class].class_skills.keys(): if self.data.data['classes'][selected_class].class_skills[skill] == [ True, False ] and not self.default_radio: self.default_radio.append(gtk.RadioButton(group=None, label=skill)) elif self.data.data['classes'][selected_class].class_skills[skill] == [ True, False ] and self.default_radio: self.default_radio.append(gtk.RadioButton(group=self.default_radio[0], label=skill)) if self.default_radio: for radio in self.default_radio: self.trained_by_default_hbox.add(radio) self.trained_by_default_hbox.show_all() self.trained_by_default_hbox and self.trained_by_default_label, as well as self.default_radio stem from the above function's class. I have two print statements (PRINT 1 and PRINT 2) in there for debugging. Here's what they give me: PRINT 1: [<gtk.Label object at 0x8fc4c84 (GtkLabel at 0x90a2f20)>, <gtk.RadioButton object at 0x8fc4d4c (GtkRadioButton at 0x90e4018)>, <gtk.RadioButton object at 0x8fc4cac (GtkRadioButton at 0x90ceec0)>] PRINT 2: [<gtk.Label object at 0x8fc4c84 (GtkLabel at 0x90a2f20)>] So the buttons have indeed been removed, yet they still show up on the page. I know the code requires some refactoring, but first I'd like to get it to work at all... If someone could help me out that would be great! Thanks a lot in advance for your replies - any kind of help is highly appreciated.

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  • How do "and" and "or" work when combined in one statement?

    - by orokusaki
    For some reason this function confused me: def protocol(port): return port == "443" and "https://" or "http://" Can somebody explain the order of what's happening behind the scenes to make this work the way it does. I understood it as this until I tried it: Either A) def protocol(port): if port == "443": if bool("https://"): return True elif bool("http://"): return True return False Or B) def protocol(port): if port == "443": return True + "https://" else: return True + "http://" Is this some sort of special case in Python, or am I completely misunderstanding how statements work?

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  • Sort string based upon the count of characters Options

    - by prp
    Sample Data : input : "abcdacdc" Output : "cadb" here we have to sort strings in order of count of characters. If the count is same for characters. maintain the original order of the characters from input string. my approach: i have used array of 26 for maintaining occurrence of all characters and sort it then print it.But while doing so i am not able to maintain order in case if two characters have same count. please suggest any improvement or any other algo.

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  • Is Unit Testing worth the effort?

    - by The Talking Walnut
    I am working to integrate unit testing into the development process on the team I work on and there are some skeptics. What are some good ways to convince the skeptical developers on the team of the value of Unit Testing? In my specific case we would be adding Unit Tests as we add functionality or fixed bugs. Unfortunately our code base does not lend itself to easy testing.

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  • How can i give password validation in flex

    - by praveen
    I want the validator for password text input. At least one Upper case letter At least one numeric character At least one special character such as @, #, $, etc. should be there in password how can i give it in action script or mxml.please help me. Thanks.

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  • Make dialogs compatible with "large fonts".

    - by Narcís Calvet
    Which do you think are best practices for making a windows dialog compatible both with standard fonts (96 dpi) and "large fonts" setting (120 dpi) so that objects don't overlap or get cut off? BTW: Just in case it's relevant, I'm interested in doing this for Delphi dialogs. Thanks in advance!

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  • Check in Javascript if a SSL Certificate is valid

    - by MB
    Hi. Is there a way to check in Javascript if given a host it's SSL certificate is valid? (non blocking) In my case I want to display: "you can also use https://.." if via javascript I can make a request to https://my_url without being asked to accept an untrusted certificate. Can this be done asynchonously? -- M.

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  • Silverlight - round doubles away from zero

    - by Cornel
    In Silverlight the Math.Round() method does not contain an overload with 'MidpointRounding' parameter. What is the best approach to round a double away from zero in Silverlight in this case? Example: Math.Round(1.4) = 1 Math.Round(1.5) = 2 Math.Round(1.6) = 2

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  • HTML Canvas and saving the data on the server

    - by snitko
    Say I've written a simple app that draws circles in browser. Now I'd like to let people save their pictures. How would I store the data on the server? Which format would be the best option? Should I simply store the relevant html? What would be the case when I would want to make a custom format that is stored on the server and parsed back to html canvas when loaded?

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  • Regex not being greedy enough

    - by Chad
    I've got the following regex that was working perfectly until a new situation arose ^.*[?&]U(?:RL)?=(?<URL>.*)$ Basically, it's used against URLs, to grab EVERYTHING after the U=, or URL= and return it in the URL match So, for the following http://localhost?a=b&u=http://otherhost?foo=bar URL = http://otherhost?foo=bar Unfortunately an odd case came up http://localhost?a=b&u=http://otherhost?foo=bar&url=http://someotherhost Ideally, I want URL to be "http://otherhost?foo=bar&url=http://someotherhost", instead, it is just "http://someotherhost"

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  • How can I stop user from navigating to the previous page

    - by ryanlancer
    Hi, I am developing a simple email portal as my college assignment and I refer gmail for various features.Now when we sign into a gmail account and then if we hit the back button of the browser we somehow still remain on the inbox page.In my case after login if I press back button I comeback to the login page.Please suggest how can I achieve this.Also I am a newbie to ASP.NET so keep it detailed

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  • Lucene based database search engine

    - by Abhay
    Hi All, I am planing to add search feature in my web application. Now the items that will be searched are strored in a Relational database. In order to achieve a full text search engine I have following doubts : For database based search engine should I use just lucene or some other utility based on Luncene like Solr, luSql, Compass etc. In case of Solr, can it be embeded in to the web applcation rather than deploying it as a seaparate WAR. Thanks for your time. regards

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  • Update Params in Python During Infinite Loop

    - by python Dude
    Hello, I was hoping to get some help on a question. I have an infinite loop that I need run and I need to update a set of variables (x in this case) at random times from the command-line. Is there any way to do this? For example: x = 0 while True: x = x + 1 if x < 30: do something and I need to update x's value from the command-line periodically

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  • Exposing members or make them private in Python?

    - by deamon
    Is there a general convention about exposing members in Python classes? I know that this is a case of "it depends", but maybe there is a rule of thumb. Private member: class Node: def __init__(self): self.__childs = [] def add_childs(self, *args): self.__childs += args node = Node() node.add_childs("one", "two") Public member: class Node2: def __init__(self): self.childs = [] node2 = Node2() node2.childs += "one", "two"

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  • Javascript date comparison

    - by Art
    Why does equality operator return false in the first case? var a = new Date(2010, 10, 10); var b = new Date(2010, 10, 10); alert(a == b); // <- returns false alert(a.getTime() == b.getTime()); // returns true Why?

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  • how not to update timestamp field

    - by GOsha
    project is written on php. There is timestamp field in mysql it updates automatically. In one case I don`t need update this field. Can I gibe instruction not to update this field in this queries without getting timestamp value.

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  • regarding C++ stl container swap function

    - by sm1
    I recently learned that all stl containers have swap function: i.e. c1.swap(c2); will lead to object underlying c1 being assigned to c2 and vice versa. I asked my professor if same is true in case of c1 and c2 being references. he said same mechanism is followed. I wonder how it happens since c++ references cannot be reseted.

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