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• How Optimize sql query make it faster

  - by user502083

  Hello every one : I have a very simple small database, 2 of tables are: Node (Node_ID, Node_name, Node_Date) : Node_ID is primary key Citation (Origin_Id, Target_Id) : PRIMARY KEY (Origin_Id, Target_Id) each is FK in Node Now I write a query that first find all citations that their Origin_Id has a specific date and then I want to know what are the target dates of these records. I'm using sqlite in python the Node table has 3000 record and Citation has 9000 records, and my query is like this in a function: def cited_years_list(self, date): c=self.cur try: c.execute("""select n.Node_Date,count(*) from Node n INNER JOIN (select c.Origin_Id AS Origin_Id, c.Target_Id AS Target_Id, n.Node_Date AS Date from CITATION c INNER JOIN NODE n ON c.Origin_Id=n.Node_Id where CAST(n.Node_Date as INT)={0}) VW ON VW.Target_Id=n.Node_Id GROUP BY n.Node_Date;""".format(date)) cited_years=c.fetchall() self.conn.commit() print('Cited Years are : \n ',str(cited_years)) except Exception as e: print('Cited Years retrival failed ',e) return cited_years Then I call this function for some specific years, But it's crazy slowwwwwwwww :( (around 1 min for a specific year) Although my query works fine, it is slow. would you please give me a suggestion to make it faster? I'd appreciate any idea about optimizing this query :) I also should mention that I have indices on Origin_Id and Target_Id, so the inner join should be pretty fast, but it's not!!!

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• Java Receive Attachment problem ?

  - by Karthick RM

  Hi to all.I use the following code to download the attachment from the mail .But it gives the ClassCastException on the Multipart declaration Exception in thread "main" java.lang.ClassCastException: com.sun.mail.imap.IMAPInputStream cannot be cast to javax.mail.Multipart at ReadAttachment.main(ReadAttachment.java:52) How do I handle IMAPInputStream? Thanks in advance !!! Message messages[] = inbox.getMessages(); for (int j = 0; j < messages.length; j++) { String mailType = messages[j].getContentType(); System.out.println("------------ Message " + (j + 1) + " ------------"); System.out.println("SentDate : " + messages[j].getSentDate()); System.out.println("From : " + messages[j].getFrom()[0]); System.out.println("Subject : " + messages[j].getSubject()); System.out.println("Type :" + messages[j].getContentType()); System.out.println("Attachment :" + messages[j].getFileName()); Multipart mp = (Multipart) messages[j].getContent(); ........... .............. System.out.println(); }

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• Howto use predicates in LINQ to Entities for Entity Framework objects

  - by user274947

  I'm using LINQ to Entities for Entity Framework objects in my Data Access Layer. My goal is to filter as much as I can from the database, without applying filtering logic on in-memory results. For that purpose Business Logic Layer passes a predicate to Data Access Layer. I mean Func<MyEntity, bool> So, if I use this predicate directly, like public IQueryable<MyEntity> GetAllMatchedEntities(Func<MyEntity, Boolean> isMatched) { return qry = _Context.MyEntities.Where(x => isMatched(x)); } I'm getting the exception [System.NotSupportedException] --- {"The LINQ expression node type 'Invoke' is not supported in LINQ to Entities."} Solution in that question suggests to use AsExpandable() method from LINQKit library. But again, using public IQueryable<MyEntity> GetAllMatchedEntities(Func<MyEntity, Boolean> isMatched) { return qry = _Context.MyEntities.AsExpandable().Where(x => isMatched(x)); } I'm getting the exception Unable to cast object of type 'System.Linq.Expressions.FieldExpression' to type 'System.Linq.Expressions.LambdaExpression' Is there way to use predicate in LINQ to Entities query for Entity Framework objects, so that it is correctly transformed it into a SQL statement. Thank you.

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• OOP design issue: Polymorphism

  - by Graham Phillips

  I'm trying to solve a design issue using inheritance based polymorphism and dynamic binding. I have an abstract superclass and two subclasses. The superclass contains common behaviour. SubClassA and SubClassB define some different methods: SubClassA defines a method performTransform(), but SubClassB does not. So the following example 1 var v:SuperClass; 2 var b:SubClassB = new SubClassB(); 3 v = b; 4 v.performTransform(); would cause a compile error on line 4 as performTransform() is not defined in the superclass. We can get it to compile by casting... (v as SubClassA).performTransform(); however, this will cause a runtime exception to be thrown as v is actually an instance of SubClassB, which also does not define performTransform() So we can get around that by testing the type of an object before casting it: if( typeof v == SubClassA) { (cast v to SubClassA).performTransform(); } That will ensure that we only call performTransform() on v's that are instances of SubClassA. That's a pretty inelegant solution to my eyes, but at least its safe. I have used interface based polymorphism (interface meaning a type that can't be instantiated and defines the API of classes that implement it) in the past, but that also feels clunky. For the above case, if SubClassA and SubClassB implemented ISuperClass that defined performTransform, then they would both have to implement performTransform(). If SubClassB had no real need for a performTransform() you would have to implement an empty function. There must be a design pattern out there that addresses the issue.

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• BufferedImage.getGraphics() resulting in memory leak, is there a fix?

  - by user359202

  Hi friends, I'm having problem with some framework API calling BufferedImage.getGraphics() method and thus causing memory leak. What this method does is that it always calls BufferedImage.createGraphics(). On a windows machine, createGraphics() is handled by Win32GraphicsEnvironment which keeps a listeners list inside its field displayChanger. When I call getGraphics on my BufferedImage someChart, someChart's SurfaceManager(which retains a reference to someChart) is added to the listeners map in Win32GraphicsEnvironment, preventing someChart to be garbage collected. Nothing afterwards removes someChart's SurfaceManager from the listeners map. In general, the summarized path stopping a BufferedImage from being garbage collected, once getGraphics is called, is as follows: GC Root - localGraphicsEnvironment(Win32GraphicsEnvironment) - displayChanger(SunDisplayChanger) - listeners(Map) - key(D3DChachingSurfaceManager) - bImg(BufferedImage) I could have changed the framework's code so that after every called to BufferedImage.getGraphics(), I keep a reference to the BufferedImage's SurfaceManager. Then, I get hold of localGraphicsEnvironment, cast it to Win32GraphicsEnvironment, then call removeDisplayChangedListener() using the reference to the BufferedImage's SurfaceManager. But I don't think this is a proper way to solve the problem. Could someone please help me with this issue? Thanks a lot!

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• Trying to write priority queue in Java but getting "Exception in thread "main" java.lang.ClassCastEx

  - by Dan

  For my data structure class, I am trying to write a program that simulates a car wash and I want to give fancy cars a higher priority than regular ones using a priority queue. The problem I am having has something to do with Java not being able to type cast "Object" as an "ArrayQueue" (a simple FIFO implementation). What am I doing wrong and how can I fix it? public class PriorityQueue<E> { private ArrayQueue<E>[] queues; private int highest=0; private int manyItems=0; public PriorityQueue(int h) { highest=h; queues = (ArrayQueue[]) new Object[highest+1]; <----problem is here } public void add(E item, int priority) { queues[priority].add(item); manyItems++; } public boolean isEmpty( ) { return (manyItems == 0); } public E remove() { E answer=null; int counter=0; do { if(!queues[highest-counter].isEmpty()) { answer = queues[highest-counter].remove(); counter=highest+1; } else counter++; }while(highest-counter>=0); return answer; } }

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• How can I extend a LINQ-to-SQL class without having to make changes every time the code is generated

  - by csharpnoob

  Hi, Update from comment: I need to extend linq-to-sql classes by own parameters and dont want to touch any generated classes. Any better suggestes are welcome. But I also don't want to do all attributes assignments all time again if the linq-to-sql classes are changing. so if vstudio generates new attribute to a class i have my own extended attributes kept separate, and the new innerited from the class itself Original question: i'm not sure if it's possible. I have a class car and a class mycar extended from class car. Class mycar has also a string list. Only difference. How can i cast now any car object to a mycar object without assigning all attributes each by hand. Like: Car car = new Car(); MyCar mcar = (MyCar) car; or MyCar mcar = new MyCar(car); or however i can extend car with own variables and don't have to do always Car car = new Car(); MyCar mcar = new MyCar(); mcar.name = car.name; mcar.xyz = car.xyz; ... Thanks.

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• C# Type conversion between two similar Datatable objects

  - by Ali

  I have .NET project with sync framework and two separate Datasets for MS SQL and Compact SQL. in my base class I have a generic DataTable object. in my derived classed I assign Typed DataTable to the generic object based on whether the application is operating online or offline: example: if (online) _dataTable = new MSSQLDataSet.Customer; else _dataTable = new CompactSQLDataSet.Customer; Now every where in my code i have to check and do a cast based on the current network mode like this: public void changeCustomerID(int ID) { if (online) (MSSQLDataSet.CustomerDataTable)_dataTable)[i].CustomerID = value; else (CompactMSSQLDataSet.CustomerDataTable)_dataTable)[i].CustomerID = value; } but I don't think this is very efficient and I believe it can be done in a smarter way to only use one line of code by dynamically getting the Type of _dataTable on the run time. my problem is at the design time, in order to acess datatable porperties such as "CustomerID" it has to be casted to either MSSQLDataSet.CustomerDataTable or CompactMSSQLDataSet.CustomerDataTable. Is there a way to have a function or a operator to convert the _datatable to its runtime type but still be able to use it's design time properties which are the same between the two types? something like: ((aType)_dataTable)[i].CustomerID = value; //or GetRuntimeType(_dataTable)[i].CustomerID = value;

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• How can I include DBNull as a value in my strongly typed dataset?

  - by Beska

  I've created a strongly typed dataset (MyDataSet) in my .NET app. For the sake of simplicity, we'll say it has one DataTable (MyDataTable), with one column (MyCol). MyCol has its DataType property set to "System.Int32", and its AllowDBNull property set to "true". I'd like to manually create a new row, and add it to this dataset. I create the row without a problem, with something like: MyDataSet.MyDataTableRow myRow = MySimpleDataSet.MyDataTable.NewItemRow(); Fine. However, when I try to set the value to DBNull: myRow.MyCol = DBNull.Value; I'm told that I can't do it...that it can't cast that to an int. This makes sense, in a way, since I've defined it to be an int...but then how can I get DBNull in there? Am I not supposed to be able to have DBNull in there? Isn't that what the AllowDBNull property is for? I'm obviously missing something fundemental. Can someone help explain what it is? EDIT: I also tried entering "int?" as the DataType, but Visual Studio throws an error when I enter it, saying that "Column requires a valid DataType."

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• Using different numeric variable types

  - by DataPimp

  Im still pretty new so bear with me on this one, my question(s) are not meant to be argumentative or petty but during some reading something struck me as odd. Im under the assumption that when computers were slow and memory was expensive using the correct variable type was much more of a necessity than it is today. Now that memory is a bit easier to come by people seem to have relaxed a bit. For example, you see this sample code everywhere: for (int i = 0; i < length; i++) int? (-2,147,483,648 to 2,147,483,648) for length? Isnt byte (0-255) a better choice? So Im curious of your opinion and what you believe to be best practice, I hate to think this would be used only because the acronym "int" is more intuitive for a beginner...or has memory just become so cheap that we really dont need to concern ourselves with such petty things and therefore we should just use long so we can be sure any other numbers/types(within reason) used can be cast automagically? ...or am Im just being silly by concerning myself with such things?

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• Is there a general-purpose printf-ish routine defined in any C standard

  - by supercat

  In many C libraries, there is a printf-style routine which is something like the following: int __vgprintf(void *info, (void)(*print_function(void*, char)), const char *format, va_list params); which will format the supplied string and call print_function with the passed-in info value and each character in sequence. A function like fprintf will pass __vgprintf the passed-in file parameter and a pointer to a function which will cast its void* to a FILE* and output the passed-in character to that file. A function like snprintf will create a struct holding a char* and length, and pass the address of that struct to a function which will output each character in sequence, space permitting. Is there any standard for such a function, which could be used if e.g. one wanted a function to output an arbitrary format to a TCP port? A common approach is to allocate a buffer one hopes is big enough, use snprintf to put the data there, and then output the data from the buffer. It would seem cleaner, though, if there were a standard way to to specify that the print formatter should call a user-supplied routine with each character.

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• Why can't I extract a C++ type from a Python type using boost::python::extractor?

  - by Robin

  I've wrapped a C++ class using Py++ and everything is working great in Python. I can instantiate the c++ class, call methods, etc. I'm now trying to embed some Python into a C++ application. This is also working fine for the most-part. I can call functions on a Python module, get return values, etc. The python code I'm calling returns one of the classes that I wrapped: import _myextension as myext def run_script(arg): my_cpp_class = myext.MyClass() return my_cpp_class I'm calling this function from C++ like this: // ... excluding error checking, ref counting, etc. for brevity ... PyObject *pModule, *pFunc, *pArgs, *pReturnValue; Py_Initialize(); pModule = PyImport_Import(PyString_FromString("cpp_interface")); pFunc = PyObject_GetAttrString(pModule, "run_script"); pArgs = PyTuple_New(1); PyTuple_SetItem(pArgs, 0, PyString_FromString("an arg")); pReturnValue = PyObject_CallObject(pFunc, pArgs); bp::extract< MyClass& > extractor(pReturnValue); // PROBLEM IS HERE if (extractor.check()) { // This check is always false MyClass& cls = extractor(); } The problem is the extractor never actually extracts/converts the PyObject* to MyClass (i.e. extractor.check() is always false). According to the docs this is the correct way to extract a wrapped C++ class. I've tried returning basic data types (ints/floats/dicts) from the Python function and all of them are extracted properly. Is there something I'm missing? Is there another way to get the data and cast to MyClass?

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• SQL Server: Can you help me with this query?

  - by rlb.usa

  I want to run a diagnostic report on our MS SQL 2008 database server. I am looping through all of the databases, and then for each database, I want to look at each table. But, when I go to look at each table (with tbl_cursor), it always picks up the tables in the database 'master'. I think it's because of my tbl_cursor selection : SELECT table_name FROM information_schema.tables WHERE table_type = 'base table' How do I fix this? Here's the entire code: SET NOCOUNT ON DECLARE @table_count INT DECLARE @db_cursor VARCHAR(100) DECLARE database_cursor CURSOR FOR SELECT name FROM sys.databases where name<>N'master' OPEN database_cursor FETCH NEXT FROM database_cursor INTO @db_cursor WHILE @@Fetch_status = 0 BEGIN PRINT @db_cursor SET @table_count = 0 DECLARE @table_cursor VARCHAR(100) DECLARE tbl_cursor CURSOR FOR SELECT table_name FROM information_schema.tables WHERE table_type = 'base table' OPEN tbl_cursor FETCH NEXT FROM tbl_cursor INTO @table_cursor WHILE @@Fetch_status = 0 BEGIN DECLARE @table_cmd NVARCHAR(255) SET @table_cmd = N'IF NOT EXISTS( SELECT TOP(1) * FROM ' + @table_cursor + ') PRINT N'' Table ''''' + @table_cursor + ''''' is empty'' ' --PRINT @table_cmd --debug EXEC sp_executesql @table_cmd SET @table_count = @table_count + 1 FETCH NEXT FROM tbl_cursor INTO @table_cursor END CLOSE tbl_cursor DEALLOCATE tbl_cursor PRINT @db_cursor + N' Total Tables : ' + CAST( @table_count as varchar(2) ) PRINT N'' -- print another blank line SET @table_count = 0 FETCH NEXT FROM database_cursor INTO @db_cursor END CLOSE database_cursor DEALLOCATE database_cursor SET NOCOUNT OFF

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• I'm graduating with a Computer Science degree but I don't feel like I know how to program.

  - by Wendy Peters

  I'm graduating with a Computer Science degree but I see websites like Stackoverflow and search engines like Google and don't know where I'd even begin to write something like that. During one summer I worked as a iPhone developer, but I felt like I was mostly gluing together libraries that other people had written with little understanding of what's happening underneath the hood. I'm trying to improve my knowledge by studying algorithms, but it is a long and painful process. I find algorithms difficult and at the rate I am working through my book it will a decade will have passed before I will finish. Given my current situation, I've spent a month looking for work but my skills (C, Python, Objective-C) are not so desirable in the local market, where C#, Java, and web development are much higher in demand. My GPA is ok (3.0) but it's not high enough to apply to the large companies or return for graduate studies and I don't have a good network of friends. Basically I'm graduating with a Computer Science degree but I don't feel like I know how to program. I thought that joining a company and programming full-time would give me a chance to develop my skills and learn from those more experienced than myself, but I'm struggling to find work and am starting to get really frustrated. I am going to cast my net wider and look beyond the city I've grown up in, but what have other people in similar situation tried to do?

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• Java generics question with wildcards

  - by Sean

  Just came across a place where I'd like to use generics and I'm not sure how to make it work the way I want. I have a method in my data layer that does a query and returns a list of objects. Here's the signature. public List getList(Class cls, Map query) This is what I'd like the calling code to look like. List<Whatever> list = getList(WhateverImpl.class, query); I'd like to make it so that I don't have to cast this to a List coming out, which leads me to this. public <T> List<T> getList(Class<T> cls, Map query) But now I have the problem that what I get out is always the concrete List<WhateverImpl> passed in whereas I'd like it to be the Whatever interface. I tried to use the super keyword but couldn't figure it out. Any generics gurus out there know how this can be done?

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• Class<T> and static method Class.forName() drive me crazy.

  - by matt

  Hi, this code doesn't compile. I'm wondering what I am doing wrong: private static Importable getRightInstance(String s) throws Exception { Class<Importable> c = Class.forName(s); Importable i = c.newInstance(); return i; } where Importable is an interface and the string s is the name of an implementing class. The compiler says: ./Importer.java:33: incompatible types found : java.lang.Class<capture#964 of ?> required: java.lang.Class<Importable> Class<Importable> c = Class.forName(format(s)); thanks for any help! All the solutions Class<? extends Importable> c = Class.forName(s).asSubclass(Importable.class); and Class<? extends Importable> c = (Class<? extends Importable>) Class.forName(s); and Class<?> c = Class.forName(format(s)); Importable i = (Importable)c.newInstance(); give this error: Exception in thread "main" java.lang.IncompatibleClassChangeError: class C1 has interface Importable as super class where C1 is effectively a class implementing Importable, one of those i want to cast to Importable.

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• Quickly or concisely determine the longest string per column in a row-based data collection

  - by ccornet

  Judging from the failure of my last inquiry, I need to calculate and preset the widths of a set of columns in a table that is being made into an Excel file. Unfortunately, the string data is stored in a row-based format, but the widths must be calculated in a column-based format. The data for the spreadsheets are generated from the following two collections: var dictFiles = l.Items.Cast<SPListItem>().GroupBy(foo => foo.GetSafeSPValue("Category")).ToDictionary(bar => bar.Key); StringDictionary dictCols = GetColumnsForItem(l.Title); Where l is an SPList whose title determines which columns are used. Each SPListItem corresponds to a row of data, which are sorted into separate worksheets based on Category (hence the dictionary). The second line is just a simple StringDictionary that has the column name (A, B, C, etc.) as a key and the corresponding SPListItme field display name as the corresponding value. So for each Category, I enumerate through dictFiles[somekey] to get all the rows in that sheet, and get the particular cell data using SPListItem.Fields[dictCols[colName]]. What I am asking is, is there a quick or concise method, for any one dictFiles[somekey], to retrieve a readout of the longest string in each column provided by dictCols? If it is impossible to get both quickness and conciseness, I can settle for either (since I always have the O(n*m) route of just enumerating the collection and updating an array whenever strCurrent.Length strLongest.Length). For example, if the goal table was the following... Item# Field1 Field2 Field3 1 Oarfish Atmosphere Pretty 2 Raven Radiation Adorable 3 Sunflower Flowers Cute I'd like a function which could cleanly take the collection of items 1, 2, and 3 and output in the correct order... Sunflower, Atmosphere, Adorable Using .NET 3.5 and C# 3.0.

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• Strongly typed dynamic Linq sorting

  - by David

  I'm trying to build some code for dynamically sorting a Linq IQueryable<. The obvious way is here, which sorts a list using a string for the field name http://dvanderboom.wordpress.com/2008/12/19/dynamically-composing-linq-orderby-clauses/ However I want one change - compile time checking of field names, and the ability to use refactoring/Find All References to support later maintenance. That means I want to define the fields as f=f.Name, instead of as strings. For my specific use I want to encapsulate some code that would decide which of a list of named "OrderBy" expressions should be used based on user input, without writing different code every time. Here is the gist of what I've written: var list = from m Movies select m; // Get our list var sorter = list.GetSorter(...); // Pass in some global user settings object sorter.AddSort("NAME", m=m.Name); sorter.AddSort("YEAR", m=m.Year).ThenBy(m=m.Year); list = sorter.GetSortedList(); ... public class Sorter ... public static Sorter GetSorter(this IQueryable source, ...) The GetSortedList function determines which of the named sorts to use, which results in a List object, where each FieldData contains the MethodInfo and Type values of the fields passed in AddSort: public SorterItem AddSort(Func field) { MethodInfo ... = field.Method; Type ... = TypeOf(TKey); // Create item, add item to diction, add fields to item's List // The item has the ThenBy method, which just adds another field to the List } I'm not sure if there is a way to store the entire field object in a way that would allow it be returned later (it would be impossible to cast, since it is a generic type) Is there a way I could adapt the sample code, or come up with entirely new code, in order to sort using strongly typed field names after they have been stored in some container and retrieved (losing any generic type casting)

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• Generic that takes only numeric types (int double etc)?

  - by brandon

  In a program I'm working on, I need to write a function to take any numeric type (int, short, long etc) and shove it in to a byte array at a specific offset. There exists a Bitconverter.GetBytes() method that takes the numeric type and returns it as a byte array, and this method only takes numeric types. So far I have: private void AddToByteArray<T>(byte[] destination, int offset, T toAdd) where T : struct { Buffer.BlockCopy(BitConverter.GetBytes(toAdd), 0, destination, offset, sizeof(toAdd)); } So basically my goal is that, for example, a call to AddToByteArray(array, 3, (short)10) would take 10 and store it in the 4th slot of array. The explicit cast exists because I know exactly how many bytes I want it to take up. There are cases where I would want a number that is small enough to be a short to really take up 4 bytes. On the flip side, there are times when I want an int to be crunched down to just a single byte. I'm doing this to create a custom network packet, if that makes any ideas pop in to your heads. If the where clause of a generic supported something like "where T : int || long || etc" I would be ok. (And no need to explain why they don't support that, the reason is fairly obvious) Any help would be greatly appreciated! Edit: I realize that I could just do a bunch of overloads, one for each type I want to support... but I'm asking this question because I want to avoid precisely that :)

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• null terminating a string

  - by robUK

  Hello, gcc 4.4.4 c89 just wondering what is the standard way to null terminate a string. i.e. However, when I use the NULL I get the warning message. *dest++ = 0; *dest++ = '\0'; *dest++ = NULL; /* Warning: Assignment takes integer from pointer without a cast */ source code I am using: size_t s_strscpy(char *dest, const char *src, const size_t len) { /* Copy the contents from src to dest */ size_t i = 0; for(i = 0; i < len; i++) *dest++ = *src++; /* Null terminate dest */ *dest++ = 0; return i; } Just another quick question. I deliberately commented out the line that null terminates. However, it still correctly printed out the contents of the dest. The caller of this function would send the length of the string by either included the NULL or not. i.e. strlen(src) + 1 or stlen(src). size_t s_strscpy(char *dest, const char *src, const size_t len) { /* Copy the contents from src to dest */ size_t i = 0; /* Don't copy the null terminator */ for(i = 0; i < len - 1; i++) *dest++ = *src++; /* Don't add the Null terminator */ /* *dest++ = 0; */ return i; } Many thanks for any advice,

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• C++ Template Class Constructor with Variable Arguments

  - by david

  Is it possible to create a template function that takes a variable number of arguments, for example, in this Vector< T, C class constructor: template < typename T, uint C > Vector< T, C >::Vector( T, ... ) { assert( C > 0 ); va_list arg_list; va_start( arg_list, C ); for( uint i = 0; i < C; i++ ) { m_data[ i ] = va_arg( arg_list, T ); } va_end( arg_list ); } This almost works, but if someone calls Vector< double, 3 ( 1, 1, 1 ), only the first argument has the correct value. I suspect that the first parameter is correct because it is cast to a double during the function call, and that the others are interpreted as ints and then the bits are stuffed into a double. Calling Vector< double, 3 ( 1.0, 1.0, 1.0 ) gives the desired results. Is there a preferred way to do something like this?

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• Using complex where clause in NHibernate mapping layer

  - by JLevett

  I've used where clauses previously in the mapping layer to prevent certain records from ever getting into my application at the lowest level possible. (Mainly to prevent having to re-write lots of lines of code to filter out the unwanted records) These have been simple, one column queries, like so this.Where("Invisible = 0"); However a scenario has appeared which requires the use of an exists sql query. exists (select ep_.Id from [Warehouse].[dbo].EventPart ep_ where Id = ep_.EventId and ep_.DataType = 4 In the above case I would usually reference the parent table Event with a short name, i.e. event_.Id however as Nhibernate generates these short names dynamically it's impossible to know what it's going to be. So instead I tried using just Id, from above ep_ where Id = ep_.EventId When the code is run, because of the dynamic short names the EventPart table short name ep_ is has another short name prefixed to it, event0_.ep_ where event0_ refers to the parent table. This causes an SQL error because of the . in between event0_ and ep_ So in my EventMap I have the following this.Where("(exists (select ep_.Id from [isnapshot.Warehouse].[dbo].EventPart ep_ where Id = ep_.EventId and ep_.DataType = 4)"); but when it's generated it creates this select cast(count(*) as INT) as col_0_0_ from [isnapshot.Warehouse].[dbo].Event event0_ where (exists (select ep_.Id from [isnapshot.Warehouse].[dbo].EventPart event0_.ep_ where event0_.Id = ep_.EventId and ep_.DataType = 4) It has correctly added the event0_ to the Id Was the mapping layer where clause built to handle this and if so where am I going wrong?

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• Is there a way to find out whether a class is a direct base of another class?

  - by user176168

  Hi I'm wondering whether there is a way to find out whether a class is a direct base of another class i.e. in boost type trait terms a is_direct_base_of function. As far as I can see boost doesn't see to support this kind of functionality which leads me to think that its impossible with the current C++ standard. The reason I want it is to do some validation checking on two macro's that are used for a reflection system to specify that one class is derived from another e.g. header.h: #define BASE A #define DERIVED B class A {}; class B : public A { #include <rtti.h> }; rtti.h: // I want to check that the two macro's are correct with a compile time assert Rtti<BASE, DERIVED> m_rtti; Although the macro's seem unnecessary in this simple example in my real world scenario rtti.h is a lot more complex. One possible avenue would be to compare the size of the this pointer with the size of a this pointer cast to the base type and some how trying to figure out whether its the size of the base class itself away or something (yeah your right I don't know how that would work either! lol)

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• Context problem while loading Assemblies via Structuremap

  - by Zebi

  I want to load plugins in a smiliar way as shown here however the loaded assemblies seem not to share the same context. Trying to solve the problem I just build a tiny spike containing two assemblies. One console app and one library. The console app contains the IPlugin interface and has no references to the Plugin dll. I am scanning the plugin dir using a custom Registration convention: ObjectFactory.Initialize(x => x.Scan(s => { s.AssembliesFromPath(@"..\Plugin"); s.With(new PluginScanner()); })); public void Process(Type type, Registry registry) { if (!type.Name.StartsWith("P")) return; var instance = ObjectFactory.GetInstance(type); registry.For<IPlugin>().Add((IPlugin)instance); } Which thows an invalid cast exception saying he can not convert the plugin Type to IPlugin. public class P1 : IPlugin { public void Start() { Console.WriteLine("Hello from P1"); } } Further if I just construct the instance (which works fine by the way) and try to access ObjectFactory in the plugin ObjectFactory.WhatDoIHave() shows that they don't even share the same container instance. Experimenting around with MEF, Structuremap and loading the assembly manually whith Assembly.Load("Plugin") shows if loaded with Assembly.Load it works fine. Any ideas how I can fix this to work with StructureMaps assembly scanning?

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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