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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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  • activerecord search conditions - looking for null or false

    - by Daniel
    When doing a search in active record I'm looking for record's that do not have an archived bit set to true. Some of the archived bits are null (which are not archived) others have archived set to false. Obviously, Project.all(:conditions => {:archived => false}) misses the projects with the archived bits with null values. How can all non-archived projects be selected wtih active record?

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  • Java's getResourceAsStream() is always returning null

    - by Andreas Grech
    I have the following structure in a Java Web Application: TheProject -- [Web Pages] -- -- [WEB-INF] -- -- -- abc.txt -- -- index.jsp -- [Source Packages] -- -- [wservices] -- -- -- WS.java In WS.java, I am using the following code in a Web Method: InputStream fstream = this.getClass().getResourceAsStream("abc.txt"); But it is always returning a null. I need to read from that file, and I read that if you put the files in WEB-INF, you can access them with getResourceAsStream, yet the method is always returning a null. Any ideas of what I may be doing wrong?

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  • Cross platform /dev/null in Python

    - by Tristan
    I'm using the following code to hide stderr on Linux/OSX for a Python library I do not control that writes to stderr by default: f = open("/dev/null","w") zookeeper.set_log_stream(f) Is there an easy cross platform alternative to /dev/null? Ideally it would not consume memory since this is a long running process.

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  • Replacing special characters by null

    - by madheena
    Hi, Is there any function to replace the special characters by null in informatica if we used replacestr function, i think we should specify all special characters as follows replacestr(input,'!','~','@','#','$','%','^','&','*',null) But we dont know what are teh special characters will be coming as input. can u please let me know that which function will be suitable.

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  • how to save related models with non-null foreign key

    - by Fortress
    I have a model called user which has_one email. I put the foreign key (NOT NULL) inside users table. Now I'm trying to save it in the following way: @email = Email.new(params[:email]) @email.user = User.new(params[:user]) @email.save This raises a db exception, because the foreign key constraint is not met (NULL is inserted into email_id). How can I elegantly solve this or is my data modeling wrong?

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  • Set MdiParent to null (Nothing) in FormClosed

    - by serhio
    In my project I observed that in a FormClosed method (that handles FormClosed event) is set MdiParent = Nothing (null). This code makes (? no idea why) that OnLoad(method) on some child panels is raised. Is there any sense to set MdiParent to null (Nothing) in FormClosed?

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  • Groovy rootLoader is null

    - by Geo
    When running a groovy script from Eclipse, the following line: def rootLoader = this.class.getClassLoader().getRootLoader() is null. When I run the script directly from command line, this is not null. How can I find out why this happens?

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  • Inserting a null value into the database.

    - by J Harley
    Good Morning, Say I have an insert statement: Insert INTO tblTest (fieldOne,FieldTwo,fieldThree) VALUES ('valueOne','valueTwo','null') This statement doesn't seem to want to insert a null value into the database... I have also tried to insert the word "nothing". Has anyone any ideas how to make this work? I am using SQL server 2005.

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  • Sum and average over null values SQL Server 2008 Analysis Services

    - by Jonathan
    I have a simple problem, I think, but I have googled and can't find the solution. I have a cube that has MeasureA, MeasureB and MeasureC. Not all three measures have values for each record, sometimes they can be null, it's depending if it was applicable. Now for my totals, I need to average but the average must not take nulls into account. Any help will be much appreciated. When I view the measures, the null values show as zeros.

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  • Array returning Null values

    - by Nick Gibson
    Dunno why it is...heres the coding for it. http://pastebin.org/301343 I know theres a lot of repetitiveness in the coding...but its because the arrays were retuning null so I got tired of messing with them. Everything works until it reaches line 224, which returns null values.

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  • Evaluate empty or null JSLT c tags

    - by user338381
    How can I validate a String null or empty using the c tags of JSLT. I have a variable of name var1 and I can display it, but I want to add a comparator for validate it. I want to validate when is different of null or empty (my values are string).

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  • Difference between name != null and null != name in java?

    - by GK
    I have seen people using the following conditions interchangeably. String name; //some code if(name != null) //or if(null != name) So is there any difference in this? or both are same? I am asking this here because, i heard that there is some difference in these, but don't know what. Thanks

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