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  • What is the best practise for relational database tables in mysql?

    - by George
    Hi, I know, there is a lot of info on mysql out there. But I was not really able to find an answer to this specific and actually simple question: Let's say I have two tables: USERS (with many fields, e.g. name, street, email, etc.) and GROUPS (also with many fields) The relation is (I guess?) 1:n, that is ONE user can be a member of MANY groups. What I dis, is create another table, named USERS_GROUPS_REL. This table has only two fields: us_id (unique key of table USERS) and gr_id (unique key of table GROUPS) In PHP I do a query with join. Is this "best practice" or is there a better way? Thankful for any hint!

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  • How do I overload an operator for an enumeration in C#?

    - by ChrisHDog
    I have an enumerated type that I would like to define the , <, =, and <= operators for. I know that these operators are implictly created on the basis of the enumerated type (as per the documentation) but I would like to explictly define these operators (for clarity, for control, to know how to do it, etc...) I was hoping I could do something like: public enum SizeType { Small = 0, Medium = 1, Large = 2, ExtraLarge = 3 } public SizeType operator >(SizeType x, SizeType y) { } But this doesn't seem to work ("unexpected toke") ... is this possible? It seems like it should be since there are implictly defined operators. Any suggestions?

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  • Infix to Postfix and unary/binary operators

    - by Jaapjan
    I have a piece of code that converts an infix expression to an expression tree in memory. This works just fine. There's just one small trouble. I just connect work out how to involve the unary operators correctly (the right associative ones). With the following infix expression : +1 + +2 - -3 - -4 I would expect an RPN of: 1+2++3-4-- Yet, none of the online infix-post converters I can find handle this example in the way I would expect. Does anyone have a clear explanation of handling right associative operators, specifically the binary ones that can be mistaken for the unary ones?

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  • How to modify a given class to use const operators

    - by zsero
    I am trying to solve my question regarding using push_back in more than one level. From the comments/answers it is clear that I have to: Create a copy operator which takes a const argument Modify all my operators to const But because this header file is given to me there is an operator what I cannot make into const. It is a simple: float & operator [] (int i) { return _item[i]; } In the given program, this operator is used to get and set data. My problem is that because I need to have this operator in the header file, I cannot turn all the other operators to const, what means I cannot insert a copy operator. How can I make all my operators into const, while preserving the functionality of the already written program? Here is the full declaration of the class: class Vector3f { float _item[3]; public: float & operator [] (int i) { return _item[i]; } Vector3f(float x, float y, float z) { _item[0] = x ; _item[1] = y ; _item[2] = z; }; Vector3f() {}; Vector3f & operator = ( const Vector3f& obj) { _item[0] = obj[0]; _item[1] = obj[1]; _item[2] = obj[2]; return *this; }; Vector3f & operator += ( const Vector3f & obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return *this; }; bool operator ==( const Vector3f & obj) { bool x = (_item[0] == obj[0]) && (_item[1] == obj[1]) && (_item[2] == obj[2]); return x; } // my copy operator Vector3f(const Vector3f& obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return this; } };

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  • Bitwise operators versus .NET abstractions for bit manipulation in C# prespective

    - by Leron
    I'm trying to get basic skills in working with bits using C#.NET. I posted an example yesterday with a simple problem that needs bit manipulation which led me to the fact that there are two main approaches - using bitwise operators or using .NET abstractions such as BitArray (Please let me know if there are more build-in tools for working with bits other than BitArray in .NET and how to find more info for them if there are?). I understand that bitwise operators work faster but using BitArray is something much more easier for me, but one thing I really try to avoid is learning bad practices. Even though my personal preferences are for the .NET abstraction(s) I want to know which i actually better to learn and use in a real program. Thinking about it I'm tempted to think that .NET abstractions are not that bad at, after all there must be reason to be there and maybe being a beginner it's more natural to learn the abstraction and later on improve my skills with low level operations, but this is just random thoughts.

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  • using operators and functions for sql report charts (visual studio 2010)

    - by user1682566
    I want to create some charts using sql reporting services. But i am unable to use a lot of functions and operators in combination with my data-fields the following work(Stroke-data type is decimal): > =Fields!Stroke.Value > =Sum(Fields!Stroke.Value) > =First(Fields!Stroke.Value) > =Last(Fields!Stroke.Value) > =2+2394.12 the following dont work: > =Fields!Stroke.Value + 2 > =CStr(Fields!Stroke.Value) > =CDbl(Fields!Stroke.Value) > =Fields!Stroke.Value / Fields!Stroke.Value > =Sum(Fields!Stroke.Value) * 2 all other operators and functions(using Fields!Stroke.Value) dont work too

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  • NASM shift operators

    - by Hudson Worden
    How would you go about doing a bit shift in NASM on a register? I read the manual and it only seems to mention these operators , <<. When I try to use them NASM complains about the shift operator working on scalar values. Can you explain what a scalar value is and give an example of how to use and <<. Also, I thought there were a shr or shl operators. If they do exist can you give an example of how to use them? Thank you for your time.

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  • Recommendations with hierarchical data on non-relational databases?

    - by Luki
    I'm developing an web application that uses a non-relational database as a backend (django-nonrel + AppEngine). I need to store some hierarchical data (projects/subproject_1/subproject_N/tasks), and I'm wondering which pattern should I use. For now I thought of: Adjacency List (store the item's parent id) Nested sets (store left and right values for the item) In my case, the depth of nesting for a normal user will not exceed 4-5 levels. Also, on the UI, I would like to have a pagination for the items on the first level, to avoid to load too many items at the first page load. From what I understand so far, nested sets are great when the hierarchy is used more for displaying. Adjacency lists are great when editing on the tree is done often. In my case I guess I need the displaying more than the editing (when using nested sets, even if the display would work great, the above pagination could complicate things on editing). Do you have any thoughts and advice, based on your experience with the non-relational databases?

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  • Ternary operators and variable reassignment in PHP

    - by TomcatExodus
    I've perused the questions on ternary operators vs. if/else structures, and while I understand that under normal circumstances there is no performance loss/gain in using ternary operators over if/else structures, I've not seen any mention of this situation. Language specific to PHP (but any language agnostic details are welcome) does the interpreter reassign values in situations like this: $foo = 'bar' $foo = strlen($foo) > 3 ? substr($foo, 0, 3) : $foo; Since this would evaluate to $foo = $foo; is this inefficient, or does the interpreter simply overlook/discard this evaluation? On a side note, what about: !defined('SECURE') ? exit : null;

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  • If some standards apply when "it depends" then should I stick with custom approaches?

    - by Travis J
    If I have an unconventional approach which works better than the industry standard, should I just stick with it even though in principal it violates those standards? What I am talking about is referential integrity for relational database management systems. The standard for enforcing referential integrity is to CASCADE delete. In practice, this is just not going to work all the time. In my current case, it does not. The alternative suggested is to either change the reference to NULL, DEFAULT, or just to take NO ACTION - usually in the form of a "soft delete". I am all about enforcing referential integrity. Love it. However, sometimes it just does not fully apply to use all the standards in practice. My approach has been to slightly abandon a small part of one of those practices which is the part about leaving "hanging references" around. Oops. The trade off is plentiful in this situation I believe. Instead of having deprecated data in the production database, a splattering of "soft delete" logic all across my controllers (and views sometimes depending on how far down the chain the soft delete occurred), and the prospect of queries taking longer and longer - instead of all that - I now have a recycle bin and centralized logic. The only tradeoff is that I must explicitly manage the possibility of "hanging references" which can be done through generics with one class. Any thoughts?

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  • Algorithm for rating books: Relative perception

    - by suneet
    So I am developing this application for rating books (think like IMDB for books) using relational database. Problem statement : Let's say book "A" deserves 8.5 in absolute sense. In case if A is the best book I have ever seen, I'll most probably rate it 9.5 whereas for someone else, it might be just an average book, so he/they will rate it less (say around 8). Let's assume 4 such guys rate it 8. If there are 10 guys who are like me (who haven't ever read great literature) and they all rate it 9.5-10. This will effectively make it's cumulative rating greater than 9 (9.5*10 + 8*4) / 14 = 9.1 whereas we needed the result to be 8.5 ... How can I take care of(normalize) this bias due to incorrect perception of individuals. MyProposedSolution : Here's one of the ways how I think it could be solved. We can have a variable Lit_coefficient which tells us how much knowledge a user has about literature. If I rate "A"(the book) 9.5 and person "X" rates it 8, then he must have read books much better than "A" and thus his Lit_coefficient should be higher. And then we can normalize the ratings according to the Lit_coefficient of user. Could there be a better algorithm/solution for the same?

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  • At what point does caching become necessary for a web application?

    - by Zaemz
    I'm considering the architecture for a web application. It's going to be a single page application that updates itself whenever the user selects different information on several forms that are available that are on the page. I was thinking that it shouldn't be good to rely on the user's browser to correctly interpret the information and update the view, so I'll send the user's choices to the server, and then get the data, send it back to the browser, and update the view. There's a table with 10,000 or so rows in a MySQL database that's going to be accessed pretty often, like once every 5-30 seconds for each user. I'm expecting 200-300 concurrent users at one time. I've read that a well designed relational database with simple queries are nothing for a RDBMS to handle, really, but I would still like to keep things quick for the client. Should this even be a concern for me at the moment? At what point would it be helpful to start using a separate caching service like Memcached or Redis, or would it even be necessary? I know that MySQL caches popular queries and the results, would this suffice?

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  • Official names for pointer operators

    - by FredOverflow
    What are the official names for the operators * and & in the context of pointers? They seem to be frequently called dereference operator and address-of operator respectively, but unfortunately, the section on unary operators in the standard does not name them. I really don't want to name & address-of anymore, because & returns a pointer, not an address. (A pointer is a language mechanism, while an address is an implementation detail. Addresses are untyped, while pointers aren't, except for void*.) The standard is very clear about this: The result of the unary & operator is a pointer to its operand. Symmetry suggests to name & reference operator which is a little unfortunate because of the collision with references in C++. The fact that & returns a pointer suggests pointer operator. Are there any official sources that would confirm these (or other) namings?

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  • Why avoid increment ("++") and decrement ("--") operators in JavaScript?

    - by artlung
    I'm a big fan of Douglas Crockford's writing on JavaScript, particularly his book JavaScript: The Good Parts. It's made me a better JavaScript programmer and a better programmer in general. One of his tips for his jslint tool is this : ++ and -- The ++ (increment) and -- (decrement) operators have been known to contribute to bad code by encouraging excessive trickiness. They are second only to faulty architecture in enabling to viruses and other security menaces. There is a plusplus option that prohibits the use of these operators. This has always struck my gut as "yes, that makes sense," but has annoyed me when I've needed a looping condition and can't figure out a better way to control the loop than a while( a < 10 )do { a++ } or for (var i=0;i<10;i++) { } and use jslint. It's challenged me to write it differently. I also know in the distant past using things, in say PHP like $foo[$bar++] has gotten me in trouble with off-by-one errors. Are there C-like languages or other languages with similarities that that lack the "++" and "--" syntax or handle it differently? Are there other rationales for avoiding "++" and "--" that I might be missing? UPDATE -- April 9, 2010: In the video Crockford on JavaScript -- Part 5: The End of All Things, Douglas Crockford addresses the ++ issue more directly and with more detail. It appears at 1:09:00 in the timeline. Worth a watch.

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  • Embedded non-relational (nosql) data store

    - by Igor Brejc
    I'm thinking about using/implementing some kind of an embedded key-value (or document) store for my Windows desktop application. I want to be able to store various types of data (GPS tracks would be one example) and of course be able to query this data. The amount of data would be such that it couldn't all be loaded into memory at the same time. I'm thinking about using sqlite as a storage engine for a key-value store, something like y-serial, but written in .NET. I've also read about FriendFeed's usage of MySQL to store schema-less data, which is a good pointer on how to use RDBMS for non-relational data. sqlite seems to be a good option because of its simplicity, portability and library size. My question is whether there are any other options for an embedded non-relational store? It doesn't need to be distributable and it doesn't have to support transactions, but it does have to be accessible from .NET and it should have a small download size. UPDATE: I've found an article titled SQLite as a Key-Value Database which compares sqlite with Berkeley DB, which is an embedded key-value store library.

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  • Boost causes an invalid block while overloading new/delete operators

    - by user555746
    Hi, I have a problem which appears to a be an invalid memory block that happens during a Boost call to Boost:runtime:cla::parser::~parser. When that global delete is called on that object, C++ asserts on the memory block as an invalid: dbgdel.cpp(52): /* verify block type */ _ASSERTE(_BLOCK_TYPE_IS_VALID(pHead->nBlockUse)); An investigation I did revealed that the problem happened because of a global overloading of the new/delete operators. Those overloadings are placed in a separate DLL. I discovered that the problem happens only when that DLL is compiled in RELEASE while the main application is compiled in DEBUG. So I thought that the Release/Debug build flavors might have created a problem like this in Boost/CRT when overloading new/delete operators. So I then tried to explicitly call to _malloc_dbg and _free_dbg withing the overloading functions even in release mode, but it didn't solve the invalid heap block problem. Any idea what the root cause of the problem is? is that situation solvable? I should stress that the problem began only when I started to use Boost. Before that CRT never complained about any invalid memory block. So could it be an internal Boost bug? Thanks!

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  • operators computing direction

    - by amiad
    Hi all! I enqunterd something that I can't understand. I have this code: cout << "f1 * f1 + f2 * f1 - f1 / f2 is: "<< f1 * f1 + f2 * f1 - f1 / f2 << endl; All the "f"s are objects, and all the operators are overloaded. The weird this is that the first computarion is of the "/" operator, then the second "" and then the first "", after that - the operator "+" and at last - operator "-". So basicly - the "/" and "*" worked from right to left, and the "+" and "-" operators worked from left to right. I made another test... I checked this code: cout << "f1 * f1 / f2 is: " << f1 * f1 / f2 << endl; Now, the first operator was "*" and only then oerator "/". So now, it worked from left to right. Can someone help me underatand why is there diffrence in the directions? 10X!

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  • Which are the fundamental stack manipulation operations?

    - by Aadit M Shah
    I'm creating a stack oriented virtual machine, and so I started learning Forth for a general understanding about how it would work. Then I shortlisted the essential stack manipulation operations I would need to implement in my virtual machine: drop ( a -- ) dup ( a -- a a ) swap ( a b -- b a ) rot ( a b c -- b c a ) I believe that the following four stack manipulation operations can be used to simulate any other stack manipulation operation. For example: nip ( a b -- b ) swap drop -rot ( a b c -- c a b ) rot rot tuck ( a b -- b a b ) dup -rot over ( a b -- a b a ) swap tuck That being said however I wanted to know whether I have listed all the fundamental stack manipulation operations necessary to manipulate the stack in any possible way. Are there any more fundamental stack manipulation operations I would need to implement, without which my virtual machine wouldn't be Turing complete?

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  • Is there something special about the number 65535?

    - by Nick Rosencrantz
    2¹6-1 & 25 = 25 (or? obviously ?) A developer asked me today what is bitwise 65535 & 32 i.e. 2¹6-1 & 25 = ? I thought at first spontaneously 32 but it seemed to easy whereupon I thought for several minutes and then answered 32. 32 seems to have been the correct answer but how? 65535=2¹6-1=1111111111111111 (but it doesn't seem right since this binary number all ones should be -1(?)), 32 = 100000 but I could not convert that in my head whereupon I anyway answered 32 since I had to answer something. Is the answer 32 in fact trivial? Is in the same way 2¹6-1 & 25-1 =31? Why did the developer ask me about exactly 65535? Binary what I was asked to evaluate was 1111111111111111 & 100000 but I don't understand why 1111111111111111 is not -1. Shouldn't it be -1? Is 65535 a number that gives overflow and how do I know that?

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  • What kind of specific projects can I do to master bitwise operations in C++? Also is there a canonical book? [closed]

    - by Ford
    I don't use C++ or bitwise operations at my current job but I'm thinking of applying to companies where it is a requirement to be fluent with them (on their tests anyway). So my question is: Can anyone suggest a project which will require gaining a fluency in bitwise operations to complete? On a side note, is there a canonical book on optimization techniques using bitwise operations since that seems to be an important use of them?

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  • Is Operator Overloading supported in C

    - by caramel23
    Today when I was reading about LCC(windows) compiler I find out it has the implemention for operator overloading . I'm puzzled because after a bit of googling , it has been confirm that operator overloading ain't support in standard C , but I read some people's comment mentioning LCC is ANSI-compliant . So my real question is , is LCC really standard C or it's just like objective-c , a C variant with object-oriented feature ?

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  • Concept of bit fields

    - by user1369975
    Whenever I read a code like this: struct node { int x : 2; int p : 4; }n; with bit fields involved, I get really confused, as to how they are represented in memory, what is sizeof(n) etc., how does it differ with normal members of structures? I tried referring K&R and http://en.wikipedia.org/wiki/Bit_field but they little to remove my confusion. What concepts of bit fields am I failing to grasp?

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