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  • Extracting bool from istream in a templated function

    - by Thomas Matthews
    I'm converting my fields class read functions into one template function. I have field classes for int, unsigned int, long, and unsigned long. These all use the same method for extracting a value from an istringstream (only the types change): template <typename Value_Type> Value_Type Extract_Value(const std::string& input_string) { std::istringstream m_string_stream; m_string_stream.str(input_string); m_string_stream.clear(); m_string_stream >> value; return; } The tricky part is with the bool (Boolean) type. There are many textual representations for Boolean: 0, 1, T, F, TRUE, FALSE, and all the case insensitive combinations Here's the questions: What does the C++ standard say are valid data to extract a bool, using the stream extraction operator? Since Boolean can be represented by text, does this involve locales? Is this platform dependent? I would like to simplify my code by not writing my own handler for bool input. I am using MS Visual Studio 2008 (version 9), C++, and Windows XP and Vista.

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  • Visitor and templated virtual methods

    - by Thomas Matthews
    In a typical implementation of the Visitor pattern, the class must account for all variations (descendants) of the base class. There are many instances where the same method content in the visitor is applied to the different methods. A templated virtual method would be ideal in this case, but for now, this is not allowed. So, can templated methods be used to resolve virtual methods of the parent class? Given (the foundation): struct Visitor_Base; // Forward declaration. struct Base { virtual accept_visitor(Visitor_Base& visitor) = 0; }; // More forward declarations struct Base_Int; struct Base_Long; struct Base_Short; struct Base_UInt; struct Base_ULong; struct Base_UShort; struct Visitor_Base { virtual void operator()(Base_Int& b) = 0; virtual void operator()(Base_Long& b) = 0; virtual void operator()(Base_Short& b) = 0; virtual void operator()(Base_UInt& b) = 0; virtual void operator()(Base_ULong& b) = 0; virtual void operator()(Base_UShort& b) = 0; }; struct Base_Int : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Long : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_Short : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UInt : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_ULong : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; struct Base_UShort : public Base { void accept_visitor(Visitor_Base& visitor) { visitor(*this); } }; Now that the foundation is laid, here is where the kicker comes in (templated methods): struct Visitor_Cout : public Visitor { template <class Receiver> void operator() (Receiver& r) { std::cout << "Visitor_Cout method not implemented.\n"; } }; Intentionally, Visitor_Cout does not contain the keyword virtual in the method declaration. All the other attributes of the method signatures match the parent declaration (or perhaps specification). In the big picture, this design allows developers to implement common visitation functionality that differs only by the type of the target object (the object receiving the visit). The implementation above is my suggestion for alerts when the derived visitor implementation hasn't implement an optional method. Is this legal by the C++ specification? (I don't trust when some says that it works with compiler XXX. This is a question against the general language.)

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  • Makefile for DOS/Windows and Cygwin

    - by Thomas Matthews
    I need to have a makefile work under DOS (Windows) and Cygwin. I having problems with the makefile detecting the OS correctly and setting appropriate variables. The objective is to set variables for the following commands, then invoke the commands in rules using the variables: Delete file: rm in Cygwin, del in DOS. Remove directory: rmdir (different parameters in Cygwin and DOS) Copy file: cp in Cygwin, copy in DOS. Testing for file existance: test in Cygwin, IF EXIST in DOS. Listing contents of a file: cat in Cygwin, type in DOS. Here is my attempt, which always uses the else clause: OS_KIND = $(OSTYPE) #OSTYPE is an environment variable set by Cygwin. ifeq ($(OS_KIND), cygwin) ENV_OS = Cygwin RM = rm -f RMDIR = rmdir -r CP = cp REN = mv IF_EXIST = test -a IF_NOT_EXIST = ! test -a LIST_FILE = cat else ENV_OS = Win_Cmd RM = del -f -Q RMDIR = rmdir /S /Q IF_EXIST = if exist IF_NOT_EXIST = if not exist LIST_FILE = type endif I'm using the forward slash character, '/', as a directory separator. This is a problem with the DOS command, as it is interpreting it as program argument rather than a separator. Anybody know how to resolve this issue? Edit: I am using make with Mingw in both Windows Console (DOS) and Cygwin.

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  • Objective C iPhone save text

    - by David Maitland
    How is it possible to save text from a text field when the user quit's the app then when the user re opens the app the text appears back in the same text box, can this be done with out a save button? What code is needed for the text to be saved and what action is needed for doing this when the app is opened? Thanks, David

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  • How do the readers fields should work like?

    - by David Marko
    In release notes of CouchDB 0.11 is stated, that it supports readers fields. I guess it should work similary as in Lotus Notes. But unfortunately I cant find any documentation on this topic. Can someone point me to documentation or some brief explanation at least? Thank you David

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  • LINQ Query please help C#.Net.

    - by Paul Matthews
    I'm very new to LINQ and struggling to find the answers. I have a simple SQL query. Select ID, COUNT(ID) as Selections, OptionName, SUM(Units) as Units FROM tbl_Results GROUP BY ID, OptionName. The results I got were: '1' '4' 'Approved' '40' '2' '1' 'Rejected' '19' '3' '2' 'Not Decided' '12' Due to having to encrypt all my data in the database I'm unable to do sums. Therefore I have now brought back the data and decrypt it in the application layer. Results would be: '1' 'Approved' '10' '3' 'Not Deceided' '6' '2' 'Rejected' '19' '1' 'Approved' '15' '1' 'Approved' '5' '3' 'Not Deceided' '6' '1' 'Approved' '10' using a simple class I have called back the above results, and put them in a list class. public class results { public int ID {get;set;} public string OptionName {get;set;} public int Unit {get;set;} } I almost have the LINQ query to bring back the results like the SQL query at the top var q = from r in Results group p.Unit by p.ID int g select new {ID = g.Key, Selections = g.Count(), Units = g.Sum()}; How do I ensure my LINQ query also give me the Option Name? Also if I created a class called Statistics to hold my results how would I modify the LINQ query to give me list result set? public class results { public int ID {get;set;} public int NumberOfSelections { get; set; } public string OptionName {get;set;} public int UnitTotal {get;set;} }

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  • How to reliably retrieve tables and columns information stored in Torque Criteria object

    - by David Zhao
    Hi there, Is there a way to retrieve tables, including alias tables, and columns, including alias columns, from an Apache Torque Criteria object reliably? I understand that there is methods like: getSelectedColumns, getAsColumns(), getJoins(), etc., but for examples, getJoins() will just return a list of joined tables strings in free text, where one has to use regular expression to extract the needed joined table information out of it. Thanks in advance! David

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  • [Doxygen] How to documenting global dependencies for functions?

    - by Thomas Matthews
    I've got some C code from a 3rd party vendor (for an embedded platform) that uses global variables (for speed & space optimizations). I'm documenting the code, converting to Doxygen format. How do I put a note in the function documentation that the function requires on global variables and functions? Doxygen has special commands for annotating parameters and return values as describe here: Doxygen Special Commands. I did not see any commands for global variables. Example C code: extern unsigned char data_buffer[]; //!< Global variable. /*! Returns the next available data byte. * \return Next data byte. */ unsigned char Get_Byte(void) { static unsigned int index = 0; return data_buffer[index++]; //!< Uses global variable. } In the above code, I would like to add Doxygen comments that the function depends on the global variable data_buffer.

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  • MySQL, C++: Retrieving auto-increment ID

    - by Thomas Matthews
    I have a table with an auto-incrementing ID. After inserting a new row, I would like to retrieve the new ID. I found an article that used the MySQL function LAST_INSERT_ID(). The article says to create a new query and submit it. I'm using MySQL Connector C++, Windows XP and Vista, and Visual Studio 9. Here are my questions: Is there an API, for the connector, that will fetch the ID out of the record? Does the result set, after an insert/append, contain the new ID? The LAST_INSERT_ID is MySQL specific. Is there an SQL standard method for obtaining the new ID?

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  • [wxWidgets] How to store wxImage into database, using C++?

    - by Thomas Matthews
    I have some wxImages and I would like to store them into a BLOB (Binary Large OBject) field in a MySQL database. There are no methods in wxImage nor wxBitmap for obtaining the binary data as an array of unsigned char so I can load into the database. My current workaround is to write the image to a temporary file, then load the BLOB field directly from the file. Is there a more efficient method to load and store a wxImage object into a MySQL BLOB field? I am using MySql C++ connector 1.05, MS Visual Studio 2008, wxWidgets and C++.

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  • Why is ARG_MAX not defined via limits.h?

    - by Josh Matthews
    On Fedora Core 7, I'm writing some code that relies on ARG_MAX. However, even if I #include <limits.h>, the constant is still not defined. My investigations show that it's present in <sys/linux/limits.h>, but this is supposed to be portable across Win32/Mac/Linux, so directly including it isn't an option. What's going on here?

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  • "conveyor belt" cache architecture

    - by Andrew Matthews
    I'm producing an application with a few peculiar internal communication characteristics that make the usual suspects for data storage and transport (Qs and RDBMSs) ill-fitted. I'm wondering whether there is a product out there that matches the following characteristics: all data put into it is peristent all reads are delivered out of memory data is universally available data lives where it is most needed data is versioned (nice to have) updates are transactional (I'd like ACID characteristics) data is potentially replicated, but always in sync works on windows is based on or has bindings for .NET is really fast is really robust is redundant is scalable I'm looking at things like Microsoft codename "Velocity", but I am not sure whether it fits all of the above characteristics. Likewise, Memcached is not a perfect fit either. The current version of this app opts for an RDBMS with a signaling system for inter-system sync, but latency is too high and versioning of the DB is a pain. I need all the robustness, but with none of the trade-offs.

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  • How can I create XSD files from M documents?

    - by Andrew Matthews
    Does anyone know of a nice way to: produce XSD documents from an OSLO model consume conformant XML documents using that model and add directly into the DB created from the model? I can't see any obvious way from the current documentation, but I'm a newcomer, so I may have missed something. Thanks.

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  • RAII: Initializing data member in const method

    - by Thomas Matthews
    In RAII, resources are not initialized until they are accessed. However, many access methods are declared constant. I need to call a mutable (non-const) function to initialize a data member. Example: Loading from a data base struct MyClass { int get_value(void) const; private: void load_from_database(void); // Loads the data member from database. int m_value; }; int MyClass :: get_value(void) const { static bool value_initialized(false); if (!value_initialized) { // The compiler complains about this call because // the method is non-const and called from a const // method. load_from_database(); } return m_value; } My primitive solution is to declare the data member as mutable. I would rather not do this, because it suggests that other methods can change the member. How would I cast the load_from_database() statement to get rid of the compiler errors?

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  • Setting QTMovie attributes

    - by Josh Matthews
    I'm trying to create a QTVR movie via QTKit, and I've got all the frames in the movie. However, setting the attributes necessary doesn't seem to be having any effect. For example: NSNumber *val = [NSNumber numberWithBool:YES]; [fMovie setAttribute:val forKey:QTMovieIsInteractiveAttribute]; val = [NSNumber numberWithBool:NO]; [fMovie setAttribute:val forKey:QTMovieIsLinearAttribute]; If I then get the value of these attributes, they come up as NO and YES, respectively. The movie is editable, so I can't understand what I'm doing wrong here. How can I ensure that the attributes will actually change?

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  • Restoring using SyncBack without profiles

    - by Thomas Matthews
    I backed up my internal hard drive (C:) using SyncBack onto an external (USB) hard drive with maximum compression. I then performed a clean install of Windows Vista onto the computer. I forgot to copy the SyncBack logs before the clean install. And now when ever I try to restore a directory, the RAR/ZIP files are copied to the system hard drive instead of extracting their contents to the hard drive. Also, SyncBack is not traversing the folders during the Restore process. How can I tell SyncBack to expand the compressed files? I am running the freeware version of SyncBack. I have to create new log files (unless SyncBack put them somewhere on the external drive). My alternative is to write a program that traverses the folders on the external drive and extracts files from the RAR/ZIP files. I am using Windows Vista, Service Pack 2, and the data size prior to backup was about 200 GB. (The backup process took over 72 hours due to "hiccups").

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  • has anyone produced an in-memory GIT repository?

    - by Andrew Matthews
    I would like to be able to take advantage of the benefits of GIT (and its workflows), but without the cost of disk access - I just would like to leverage the distributed revision control capabilities of GIT to produce something like a hybrid of memcached and GIT. (preferably in .NET) Is there such a beast out there?

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  • Using child visitor in C#

    - by Thomas Matthews
    I am setting up a testing component and trying to keep it generic. I want to use a generic Visitor class, but not sure about using descendant classes. Example: public interface Interface_Test_Case { void execute(); void accept(Interface_Test_Visitor v); } public interface Interface_Test_Visitor { void visit(Interface_Test_Case tc); } public interface Interface_Read_Test_Case : Interface_Test_Case { uint read_value(); } public class USB_Read_Test : Interface_Read_Test_Case { void execute() { Console.WriteLine("Executing USB Read Test Case."); } void accept(Interface_Test_Visitor v) { Console.WriteLine("Accepting visitor."); } uint read_value() { Console.WriteLine("Reading value from USB"); return 0; } } public class USB_Read_Visitor : Interface_Test_Visitor { void visit(Interface_Test_Case tc) { Console.WriteLine("Not supported Test Case."); } void visit(Interface_Read_Test_Case rtc) { Console.WriteLine("Not supported Read Test Case."); } void visit(USB_Read_Test urt) { Console.WriteLine("Yay, visiting USB Read Test case."); } } // Code fragment USB_Read_Test test_case; USB_Read_Visitor visitor; test_case.accept(visitor); What are the rules the C# compiler uses to determine which of the methods in USB_Read_Visitor will be executed by the code fragment? I'm trying to factor out dependencies of my testing component. Unfortunately, my current Visitor class contains visit methods for classes not related to the testing component. Am I trying to achieve the impossible?

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