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  • C++: Conceptual problem in designing an intepreter

    - by sub
    I'm programming an interpreter for an experimental programming language (educational, fun,...) So far, everything went well (Tokenizer & Parser), but I'm getting a huge problem with some of the data structures in the part that actually runs the tokenized and parsed code. My programming language basically has only two types, int and string, and they are represented as C++ strings (std class) and ints Here is a short version of the data structure that I use to pass values around: enum DataType { Null, Int, String } class Symbol { public: string identifier; DataType type; string stringValue; int intValue; } I can't use union because string doesn't allow me to. This structure above is beginning to give me a headache. I have to scatter code like this everywhere in order to make it work, it is beginning to grow unmaintainable: if( mySymbol.type == Int ) { mySymbol.intValue = 1234; } else { mySymbol.stringValue = "abcde"; } I use the Symbol data structure for variables, return values for functions and general representation of values in the programming language. Is there any better way to solve this? I hope so!

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  • STLifying C++ classes

    - by shambulator
    I'm trying to write a class which contains several std::vectors as data members, and provides a subset of vector's interface to access them: class Mesh { public: private: std::vector<Vector3> positions; std::vector<Vector3> normals; // Several other members along the same lines }; The main thing you can do with a mesh is add positions, normals and other stuff to it. In order to allow an STL-like way of accessing a Mesh (add from arrays, other containers, etc.), I'm toying with the idea of adding methods like this: public: template<class InIter> void AddNormals(InIter first, InIter last); Problem is, from what I understand of templates, these methods will have to be defined in the header file (seems to make sense; without a concrete iterator type, the compiler doesn't know how to generate object code for the obvious implementation of this method). Is this actually a problem? My gut reaction is not to go around sticking huge chunks of code in header files, but my C++ is a little rusty with not much STL experience outside toy examples, and I'm not sure what "acceptable" C++ coding practice is on this. Is there a better way to expose this functionality while retaining an STL-like generic programming flavour? One way would be something like this: (end list) class RestrictedVector<T> { public: RestrictedVector(std::vector<T> wrapped) : wrapped(wrapped) {} template <class InIter> void Add(InIter first, InIter last) { std::copy(first, last, std::back_insert_iterator(wrapped)); } private: std::vector<T> wrapped; }; and then expose instances of these on Mesh instead, but that's starting to reek a little of overengineering :P Any advice is greatly appreciated!

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  • Interpreted languages: The higher-level the faster?

    - by immersion
    I have designed around 5 experimental languages and interpreters for them so far, for education, as a hobby and for fun. One thing I noticed: The assembly-like language featuring only subroutines and conditional jumps as structures was much slower than the high-level language featuring if, while and so on. I developed them both simultaneously and both were interpreted languages. I wrote the interpreters in C++ and I tried to optimize the code-execution part to be as fast as possible. My hypothesis: In almost all cases, performance of interpreted languages rises with their level (high/low). Am I basically right with this? (If not, why?)

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  • Constructors + Dependency Injection

    - by Sunny
    If I am writing up a class with more than 1 constructor parameter like: class A{ public A(Dependency1 d1, Dependency2 d2, ...){} } I usually create a "argument holder"-type of class like: class AArgs{ public Dependency1 d1 { get; private set; } public Dependency2 d2 { get; private set; } ... } and then: class A{ public A(AArgs args){} } Typically, using a DI-container I can configure the constructor for dependencies & resolve them & so there is minimum impact when the constructors need to change. Is this considered an anti-pattern and/or any arguments against doing this?

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  • One on One table relation - is it harmful to keep relation in both tables?

    - by EBAGHAKI
    I have 2 tables that their rows have one on one relation.. For you to understand the situation, suppose there is one table with user informations and there is another table that contains a very specific informations and each user can only link to one these specific kind of informations ( suppose second table as characters ) And that character can only assign to the user who grabs it, Is it against the rules of designing clean databases to hold the relation key in both tables? User Table: user_id, name, age, character_id Character Table: character_id, shape, user_id I have to do it for performance, how do you think about it?

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  • One database or many?

    - by dsims
    I am developing a website that will manage data for multiple entities. No data is shared between entities, but they may be owned by the same customer. A customer may want to manage all their entities from a single "dashboard". So should I have one database for everything, or keep the data seperated into individual databases? Is there a best-practice? What are the positives/negatives for having a: database for the entire site (entity has a "customerID", data has "entityID") database for each customer (data has "entityID") database for each entity (relation of database to customer is outside of database) Multiple databases seems like it would have better performance (fewer rows and joins) but may eventually become a maintenance nightmare.

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  • Where do you find images and graphics for your softwares ?

    - by ereOn
    Hi, As a programmer, I'm sure some of you already experienced the same problem: You create a good software (free, open-source, or for friend-only diffusion, whatever) relying on good code and good ideas but since you're a programmer and not an image designer, your program looks just bad. While it seems pretty easy to find motivated developpers to join for free an open-source project, it seems quite hard to find a single free graphic designer. What free and good resources do you usually use for your programs/websites ? Do you have any cool tip that you're willing to share ?

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  • How to set a value from another class

    - by Ram
    Its said that property should not be "Set" only and it should be "Get" as well. What should i do if I need to set value to a variable from some other class? The will keep changing so I cannot pass it through constructor. Shall I create a function for this as shown below? class A { public void SetValue() { b = new B(); b.SetTest(10); } } class B { int test; public void SetTest(int value) { test = value; } } What are the other alternatives?

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  • In what package should a "Settings" class be placed?

    - by Tom
    I'm in the middle of building an application but found myself too easily creating new packages without keeping the project's structure in mind. Now, I'm trying to redo the whole project structure on paper first. I am using a Settings class with public properties, accessed as settings for several other classes around the project. Now, since this Settings class applies for the whole project, I am unsure if it should be packaged and if so, in what kind of package should it exist? Or should it be in the root (the default package) with the main application class? I've been thinking about putting it in my utils package, then again I don't think it really is an utlity. Any strategies on how to decide on such package structure for example for a Settings class?

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  • What is the point declaring variables at the end of class?

    - by serhio
    I saw multiple examples in MSDN that uses to declare the internal fields at the end of the class. What is the point? I find this a little embarrassing, because each time Visual Studio adds a method it adds it to the end of the class, so there is need every time to move it... class A { public A(){} // Methods, Properties, etc ... private string name; } class A { private string name; public A(){} // Methods, Properties, etc ... }

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  • Avoiding repetition with libraries that use a setup + execute model

    - by lijie
    Some libraries offer the ability to separate setup and execution, esp if the setup portion has undesirable characteristics such as unbounded latency. If the program needs to have this reflected in its structure, then it is natural to have: void setupXXX(...); // which calls the setup stuff void doXXX(...); // which calls the execute stuff The problem with this is that the structure of setupXXX and doXXX is going to be quite similar (at least textually -- control flow will prob be more complex in doXXX). Wondering if there are any ways to avoid this. Example: Let's say we're doing signal processing: filtering with a known kernel in the frequency domain. so, setupXXX and doXXX would probably be something like... void doFilter(FilterStuff *c) { for (int i = 0; i < c->N; ++i) { doFFT(c->x[i], c->fft_forward_setup, c->tmp); doMultiplyVector(c->tmp, c->filter); doFFT(c->tmp, c->fft_inverse_setup, c->x[i]); } } void setupFilter(FilterStuff *c) { setupFFT(..., &(c->fft_forward_setup)); // assign the kernel to c->filter ... setupFFT(..., &(c->fft_inverse_setup)); }

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  • is Payment table needed when you have an invoice table like this?

    - by EBAGHAKI
    this is my invoice table: Invoice Table: invoice_id creation_date due_date payment_date status enum('not paid','paid','expired') user_id total_price I wonder if it's Useful to have a payment table in order to record user payments for invoices. payment table can be like this: payment_id payment_date invoice_id price_paid status enum('successful', 'not successful')

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  • Singletons and constants

    - by devoured elysium
    I am making a program which makes use of a couple of constants. At first, each time I needed to use a constant, I'd define it as //C# private static readonly int MyConstant = xxx; //Java private static final int MyConstant = xxx; in the class where I'd need it. After some time, I started to realise that some constants would be needed in more than one class. At this time, I had 3 choises: To define them in the different classes that needed it. This leads to repetition. If by some reason later I need to change one of them, I'd have to check in all classes to replace them everywhere. To define a static class/singleton with all the constants as public. If I needed a constant X in ClassA, ClassB and ClassC, I could just define it in ClassA as public, and then have ClassB and ClassC refer to them. This solution doesn't seem that good to me as it introduces even more dependencies as the classes already have between them. I ended up implementing my code with the second option. Is that the best alternative? I feel I am probably missing some other better alternative. What worries me about using the singleton here is that it is nowhere clear to a user of the class that this class is using the singleton. Maybe I could create a ConstantsClass that held all the constants needed and then I'd pass it in the constructor to the classes that'd need it? Thanks

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  • Handling missing data

    - by soppotare
    Say I have a simple helpdesk application which logs calls made by users. I would typically have such fields in a table relating to the call e.g. CallID, Description, CustomerID etc. I Would also have a table of customers including CustomerID, Username, Password, FullName etc. Now when a user is deleted from the customers table then the inner join between the calls table and the users table to find out historically which user logged a call would produce no results. How do people usually deal with this? Have seperate customer and useraccount tables Just disable the accounts so the data is still available Record the customers name in the calls table as a seperate field. or any other methods / suggestions?

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  • Which controls are being used?

    - by Jack
    Are there any tools available that allow you to 'look' at any given application and show you which WinForm controls are being used in that application? I happen to have an app which I like the GUI of, and I want to use a similar structure in my own app. Instead of developing these controls myself, it may be easier to buy them, if only I can spot which are being used... Any suggestions?

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  • What sort of schema can I use to accommodate manual date based data entries?

    - by meder
    I have an admin where users from multiple properties can enter in monthly statistics for twitter/facebook followers. We do not have access to the real data/db so this is why a manual entry. The form looks like this: Type ( radio, select **one** only ): - Twitter - Facebook Followers/Fans ( textfield ): Property (dropdown): Hotel A, Hotel B Date Start: mm/dd/yyyy (textfield) Date End: mm/dd/yyyy (textfield) Question 1.1: Since I am only keeping track of month per month, the date start/end fields which I have already created might be too specific. Would it be a better idea just to have a start month/year and and month/year if that's the only thing I care about? Question 1.2: What schema could I use for month to month statistics if I were to change the date start and end textfields to start month/year and end month/year dropdowns?

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  • Splitting values into groups evenly

    - by Paul Knopf
    Let me try to explain the situation the best I can. Lets say I have 3 values 1, 2, 3 I tell an algorithm to split this values into x columns. Lets say x = 2 for clarification. The algorithm determines that the group of values is best put into two columns the following way. 1st column 2nd column --------------------------- 1 3 2 Each column has an even number (totals, not literals) value. Now lets say I have the following values 7, 8, 3, 1, 4 I tell the algorithm that I want the values split into 3 columns. The algorithm now tells me that the following is the best fit. 1st column 2nd column 3rd column 8 7 3 1 4 Notice how the columns arent quiet even, but it is as close as it can get. A little over and a little under is considered ok, as long as the list is AS CLOSE TO EVEN AS IT CAN BE. Anybody got any suggestions? Know any good methods of doing this?

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