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  • Execute a function to affect different template class instances

    - by Samer Afach
    I have a complicated problem, and I need help. I have a base case, class ParamBase { string paramValue; //... } and a bunch of class templates with different template parameters. template <typename T> class Param : public ParamBase { T value; //... } Now, each instance of Param has different template parameter, double, int, string... etc. To make it easier, I have a vector to their base class pointers that contains all the instances that have been created: vector<ParamBase*> allParamsObjects; The question is: How can I run a single function (global or member or anything, your choice), that converts all of those different instances' strings paramValue with different templates arguments and save the conversion result to the appropriate type in Param::value. This has to be run over all objects that are saved in the vector allParamsObjects. So if the template argument of the first Param is double, paramValue has to be converted to double and saved in value; and if the second Param's argument is int, then the paramValue of the second has to be converted to int and saved in value... etc. I feel it's almost impossible... Any help would be highly appreciated :-)

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  • Link error for user defined class type template parameter

    - by isurulucky
    Hi, I implemented a Simple STL map in C++. Factored out the comparison as a type as I was instructed to, then implemented the comparison as shown below: template <typename T> int KeyCompare<T>::operator () (T tKey1, T tKey2) { if(tKey1 < tKey2) return -1; else if(tKey1 > tKey2) return 1; else return 0; } here, tKey1 and tKet2 are the two keys I'm comparing. This worked well for all the basic data types and string. I added a template specialization to compare keys of a user defined type named Test and added a specialization as follows: int KeyCompare<Test>::operator () (Test tKey1, Test tKey2) { if(tKey1.a < tKey2.a) return -1; else if(tKey1.a > tKey2.a) return 1; else return 0; } when I run this, I get a linking error saying SimpleMap.obj : error LNK2005: "public: int __thiscall KeyCompare::operator()(class Test,class Test)" (??R?$KeyCompare@VTest@@@@QAEHVTest@@0@Z) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::~KeyCompare(void)" (??1?$KeyCompare@VTest@@@@QAE@XZ) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::KeyCompare(void)" (??0?$KeyCompare@VTester@@@@QAE@XZ) already defined in MapTest.obj MapTest.cpp is the test harness class in which I wrote the test case. I have used include guards as well, to stop multiple inclusions. Any idea what the matter is?? Thank you very much!!

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  • adding virtual function to the end of the class declaration avoids binary incompatibility?

    - by bob
    Could someone explain to me why adding a virtual function to the end of a class declaration avoids binary incompatibility? If I have: class A { public: virtual ~A(); virtual void someFuncA() = 0; virtual void someFuncB() = 0; virtual void other1() = 0; private: int someVal; }; And later modify this function to: class A { public: virtual ~A(); virtual void someFuncA(); virtual void someFuncB(); virtual void someFuncC(); virtual void other1() = 0; private: int someVal; }; I get a coredump from another .so compiled against the previous declaration. But if I put someFuncC() at the end of the class declaration (after "int someVal"), I don't see coredump anymore. Could someone tell me why this is? And does this trick always work? PS. compiler is gcc, does this work with other compilers?

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  • Integer array or struct array - which is better?

    - by MusiGenesis
    In my app, I'm storing Bitmap data in a two-dimensional integer array (int[,]). To access the R, G and B values I use something like this: // read: int i = _data[x, y]; byte B = (byte)(i >> 0); byte G = (byte)(i >> 8); byte R = (byte)(i >> 16); // write: _data[x, y] = BitConverter.ToInt32(new byte[] { B, G, R, 0 }, 0); I'm using integer arrays instead of an actual System.Drawing.Bitmap because my app runs on Windows Mobile devices where the memory available for creating bitmaps is severely limited. I'm wondering, though, if it would make more sense to declare a structure like this: public struct RGB { public byte R; public byte G; public byte B; } ... and then use an array of RGB instead of an array of int. This way I could easily read and write the separate R, G and B values without having to do bit-shifting and BitConverter-ing. I vaguely remember something from days of yore about byte variables being block-aligned on 32-bit systems, so that a byte actually takes up 4 bytes of memory instead of just 1 (but maybe this was just a Visual Basic thing). Would using an array of structs (like the RGB example` above) be faster than using an array of ints, and would it use 3/4 the memory or 3 times the memory of ints?

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  • Nested loops through recursion with usable iterators

    - by narandzasto
    Help! I need to generate a query with loops,but there must be undefinitly numbers of loop or much as many a client wants. I know that it can be done with recursion,but don't know exectly how.One more thing. Notice,please,that I need to use those k,i,j iterators later in "if" condition and I don't know how to catch them. Thanks class Class1 { public void ListQuery() { for (int k = 0; k < listbox1.Count; k++) { for (int i = 0; i < listbox2.Count; i++) { for (int j = 0; j < listbox3.Count; j++) { if (k == listbox1.count-1 && i == listbox2.count-1 && j == listbox3.count-1) { if (!checkbox1) Query += resultset.element1 + "=" + listbox1[k]; if (!checkbox2) Query += resultset.element2 + "=" + listbox1[i]; if (!checkbox3) Query += resultset.element3 + "=" + listbox1[j]; } } } } } }

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  • MySQL - Structure for Permissions to Objects

    - by Kerry
    What would be an ideal structure for users permissions of objects. I've seen many related posts for general permissions, or what sections a user can access, which consists of a users, userGroups and userGroupRelations or something of that nature. In my system there are many different objects that can get created, and each one has to be able to be turned on or off. For instance, take a password manager that has groups and sub groups. Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9 Group 10 Each group can contain a set of passwords. A user can be given read, write, edit and delete permissions to any group. More groups can get created at any point in time. If someone has permission to a group, I should be able to make him have permissions to all sub groups OR restrict it to just that group. My current thought is to have a users table, and then a permissions table with columns like: permission_id (int) PRIMARY_KEY user_id (int) INDEX object_id (int) INDEX type (varchar) INDEX read (bool) write (bool) edit (bool) delete (bool) This has worked in the past, but the new system I'm building needs to be able to scale rapidly, and I am unsure if this is the best structure. It also makes the idea of having someone with all subgroup permissions of a group more difficult. So, as a question, should I use the above structure? Or can someone point me in the direction of a better one?

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  • Decimal problem in Java

    - by Jerome
    I am experimenting with writing a java class for financial engineering (hobby of mine). The algorithm that I desire to implement is: 100 / 0.05 = 2000 Instead I get: 100 / 0.05 = 2000.9999999999998 I understand the problem to be one with converting from binary numbers to decimals (float -- int). I have looked at the BigDecimal class on the web but have not quite found what I am looking for. Attached is the program and a class that I wrote: // DCF class public class DCF { double rate; double principle; int period; public DCF(double $rate, double $principle, int $period) { rate = $rate; principle = $principle; period = $period; } // returns the console value public double consol() { return principle/rate; } // to string Method public String toString() { return "(" + rate + "," + principle + "," + period + ")"; } } Now the actual program: // consol program public class DCFmain { public static void main(String[] args) { // create new DCF DCF abacus = new DCF(0.05, 100.05, 5); System.out.println(abacus); System.out.println("Console value= " + abacus.consol() ); } } Output: (0.05,100.05,5) Console value= 2000.9999999999998 Thanks!

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  • Search a string in a file and write the matched lines to another file in Java

    - by Geeta
    For searching a string in a file and writing the lines with matched string to another file it takes 15 - 20 mins for a single zip file of 70MB(compressed state). Is there any ways to minimise it. my source code: getting Zip file entries zipFile = new ZipFile(source_file_name); entries = zipFile.entries(); while (entries.hasMoreElements()) { ZipEntry entry = (ZipEntry)entries.nextElement(); if (entry.isDirectory()) { continue; } searchString(Thread.currentThread(),entry.getName(), new BufferedInputStream (zipFile.getInputStream(entry)), Out_File, search_string, stats); } zipFile.close(); Searching String public void searchString(Thread CThread, String Source_File, BufferedInputStream in, File outfile, String search, String stats) throws IOException { int count = 0; int countw = 0; int countl = 0; String s; String[] str; BufferedReader br2 = new BufferedReader(new InputStreamReader(in)); System.out.println(CThread.currentThread()); while ((s = br2.readLine()) != null) { str = s.split(search); count = str.length - 1; countw += count; //word count if (s.contains(search)) { countl++; //line count WriteFile(CThread,s, outfile.toString(), search); } } br2.close(); in.close(); } -------------------------------------------------------------------------------- public void WriteFile(Thread CThread,String line, String out, String search) throws IOException { BufferedWriter bufferedWriter = null; System.out.println("writre thread"+CThread.currentThread()); bufferedWriter = new BufferedWriter(new FileWriter(out, true)); bufferedWriter.write(line); bufferedWriter.newLine(); bufferedWriter.flush(); } Please help me. Its really taking 40 mins for 10 files using threads and 15 - 20 mins for a single file of 70MB after being compressed. Any ways to minimise the time.

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  • Where do objects merge/join data in a 3-tier model?

    - by BerggreenDK
    Its probarbly a simple 3-tier problem. I just want to make sure we use the best practice for this and I am not that familiary with the structures yet. We have the 3 tiers: GUI: ASP.NET for Presentation-layer (first platform) BAL: Business-layer will be handling the logic on a webserver in C#, so we both can use it for webforms/MVC + webservices DAL: LINQ to SQL in the Data-layer, returning BusinessObjects not LINQ. DB: The SQL will be Microsoft SQL-server/Express (havent decided yet). Lets think of setup where we have a database of [Persons]. They can all have multiple [Address]es and we have a complete list of all [PostalCode] and corresponding citynames etc. The deal is that we have joined a lot of details from other tables. {Relations}/[tables] [Person]:1 --- N:{PersonAddress}:M --- 1:[Address] [Address]:N --- 1:[PostalCode] Now we want to build the DAL for Person. How should the PersonBO look and when does the joins occure? Is it a business-layer problem to fetch all citynames and possible addressses pr. Person? or should the DAL complete all this before returning the PersonBO to the BAL ? Class PersonBO { public int ID {get;set;} public string Name {get;set;} public List<AddressBO> {get;set;} // Question #1 } // Q1: do we retrieve the objects before returning the PersonBO and should it be an Array instead? or is this totally wrong for n-tier/3-tier?? Class AddressBO { public int ID {get;set;} public string StreetName {get;set;} public int PostalCode {get;set;} // Question #2 } // Q2: do we make the lookup or just leave the PostalCode for later lookup? Can anyone explain in what order to pull which objects? Constructive criticism is very welcome. :o)

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  • Updating an application OTA

    - by Bostjan
    I'm developing an application that will be available from a website (market probably as well). The problem I'm having at the moment is how to handle the updates to the app. I know how to check the version against the current one and I know if I need to update it. Question is...how? Is there a way I can download an APK from the website and start the install process? The user will have to confirm of course, but I just want to be able to start it for him. At the moment I'm doing this: private void doUpgrade() { // TODO Auto-generated method stub Builder builder = new AlertDialog.Builder(this); builder.setTitle(getString(R.string.upgrade)); builder.setIcon(R.drawable.help); builder.setMessage(getString(R.string.needUpgrade)); builder.setPositiveButton(getString(R.string.ok), new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub Map<String, String> data = new HashMap<String, String>(); try { HttpResponse re = Registration.doPost("http://www.android-town.com/appRelease/AndroidTown.apk",data); int statusCode = re.getStatusLine().getStatusCode(); closeApp(); } catch (ClientProtocolException e) { e.printStackTrace(); Toast.makeText(getApplicationContext(), getString(R.string.noURLAccess), Toast.LENGTH_SHORT).show(); closeApp(); } catch (IOException e) { e.printStackTrace(); Toast.makeText(getApplicationContext(), getString(R.string.noURLAccess), Toast.LENGTH_SHORT).show(); closeApp(); } } }); builder.setNegativeButton(getString(R.string.cancel), new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub dialog.cancel(); closeApp(); } }); builder.show(); } But it doesn't really do anything...should I open a webView with the URL? A new runnable thread? Any other way? Please help :) Cheers

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  • How to use dirent.h correctly.

    - by Nick
    Hello, I am new to C++ and I am experimenting with the dirent.h header to manipulate directory entries. The following little app compiles but pukes after you supple a directory name. Can someone give me a hint? The int quit is there to provide a while loop. I removed the loop in an attempt to isolate my problem. thanks! #include <iostream> #include <dirent.h> using namespace std; int main() { char *dirname = 0; DIR *pd = 0; struct dirent *pdirent = 0; int quit = 1; cout<< "Enter a directory path to open (leave blank to quit):\n"; cin >> dirname; if(dirname == NULL) { quit = 0; } pd = opendir(dirname); if(pd == NULL) { cout << "ERROR: Please provide a valid directory path.\n"; } return 0; }

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  • C# Virtual method call in constructor - how to refactor?

    - by Cristi Diaconescu
    I have an abstract class for database-agnostic cursor actions. Derived from that, there are classes that implement the abstract methods for handling database-specific stuff. The problem is, the base class ctor needs to call an abstract method - when the ctor is called, it needs to initialize the database-specific cursor. I know why this shouldn't be done, I don't need that explanation! This is my first implementation, that obviously doesn't work - it's the textbook "wrong way" of doing it. The overridden method accesses a field from the derived class, which is not yet instantiated: public abstract class CursorReader { private readonly int m_rowCount; protected CursorReader() { m_rowCount = CreateCursor(sqlCmd); //virtual call ! } protected abstract int CreateCursor(string sqlCmd); } public class SqlCursorReader : CursorReader { private SqlConnection m_sqlConnection; public SqlCursorReader(string sqlCmd, SqlConnection sqlConnection) { m_sqlConnection = sqlConnection; //field initialized here } protected override int CreateCursor(string sqlCmd) { //uses not-yet-initialized member *m_sqlConnection* //so this throws a NullReferenceException var cursor = new CustomCursor(sqlCmd, m_sqlConnection); return cursor.Count(); } } I will follow up with an answer on my attempts to fix this...

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  • SQL n:m Inheritance join

    - by Nightmares
    I want to join a table which contains n:m relationship between groups. (Groups are defined in a separate table). This table only has entries listing a member_group_id and a parent_group_id. Given this structure: id(int) | member_group_id(int) | parent_group_id(int) The "base" query looks like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id The "base" query correctly shows all relationships (I checked by doing it manually.) The problem is when I try to apply a where clause to this query to filter for a specific group as "point of origin" (the first group for which I want all parent groups) it returns only the closest parents. For example like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id where p1.group_id = 1 Can anyone give a clue how I can fix this? Or a different approach to realize this. (I suppose I could always do this in my C++ source code on the server side but I would have to transfer a entire table which has a high growth potential to the application server.) UPDATE: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.group_id = p1.member_group_id Typing mistake confirmed. Now I don't get past first level of inheritance period. Thanks at denied for pointing that out.

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  • Getting an exception when trying to use extension method with SortedDictionary... why?

    - by Polaris878
    I'm trying to place custom objects into a sorted dictionary... I am then trying to use an extension method (Max()) on this sorted dictionary. However, I'm getting the exception: "At least one object must implement IComparable". I don't understand why I'm getting that, as my custom object obviously implements IComparable. Here is my code: public class MyDate : IComparable<MyDate> { int IComparable<MyDate>.CompareTo(MyDate obj) { if (obj != null) { if (this.Value.Ticks < obj.Value.Ticks) { return 1; } else if (this.Value.Ticks == obj.Value.Ticks) { return 0; } else { return -1; } } } public MyDate(DateTime date) { this.Value = date; } public DateTime Value; } class Program { static void Main(string[] args) { SortedDictionary<MyDate, int> sd = new SortedDictionary<MyDate,int>(); sd.Add(new MyDate(new DateTime(1)), 1); sd.Add(new MyDate(new DateTime(2)), 2); Console.WriteLine(sd.Max().Value); // Throws exception!! } } What on earth am I doing wrong???

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  • Pointing to array element

    - by regular
    What I'm trying to achieve is say i have an array, i want to be able to modify a specific array element throughout my code, by pointing at it. for example in C++ i can do this int main(){ int arr [5]= {1,2,3,4,5}; int *c = &arr[3]; cout << arr[3] <<endl; *c = 0; cout << arr[3]<<endl; } I did some googling and there seems to be a way to do it through 'unsafe', but i don't really want to go that route. I guess i could create a variable to store the indexes, but I'm actually dealing with slightly more complexity (a list within a list. so having two index variables seems to add complexity to the code.) C# has a databinding class, so what I'm currently doing is binding the array element to a textbox (that i have hidden) and modifying that textbox whenever i want to modify the specific array element, but that's also not a good solution (since i have a textbox that's not being used for its intended purpose - a bit misleading).

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  • IComparer for integers and force empty strings to end

    - by paulio
    Hi, I've written the following IComparer but I need some help. I'm trying to sort a list of numbers but some of the numbers may not have been filled in. I want these numbers to be sent to the end of the list at all times.. for example... [EMPTY], 1, [EMPTY], 3, 2 would become... 1, 2, 3, [EMPTY], [EMPTY] and reversed this would become... 3, 2, 1, [EMPTY], [EMPTY] Any ideas? public int Compare(ListViewItem x, ListViewItem y) { int comparison = int.MinValue; ListViewItem.ListViewSubItem itemOne = x.SubItems[subItemIndex]; ListViewItem.ListViewSubItem itemTwo = y.SubItems[subItemIndex]; if (!string.IsNullOrEmpty(itemOne.Text) && !string.IsNullOrEmpty(itemTwo.Text)) { uint itemOneComparison = uint.Parse(itemOne.Text); uint itemTwoComparison = uint.Parse(itemTwo.Text); comparison = itemOneComparison.CompareTo(itemTwoComparison); } else { // ALWAYS SEND TO BOTTOM/END OF LIST. } // Calculate correct return value based on object comparison. if (OrderOfSort == SortOrder.Descending) { // Descending sort is selected, return negative result of compare operation. comparison = (-comparison); } else if (OrderOfSort == SortOrder.None) { // Return '0' to indicate they are equal. comparison = 0; } return comparison; } Cheers.

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  • How to track auto-generated id's in select-insert statement

    - by k rey
    I have two tables detail and head. The detail table will be written first. Later, the head table will be written. The head is a summary of the detail table. I would like to keep a reference from the detail to the head table. I have a solution but it is not elegant and requires duplicating the joins and filters that were used during summation. I am looking for a better solution. The below is an example of what I currently have. In this example, I have simplified the table structure. In the real world, the summation is very complex. -- Preparation create table #detail ( detail_id int identity(1,1) , code char(4) , amount money , head_id int null ); create table #head ( head_id int identity(1,1) , code char(4) , subtotal money ); insert into #detail ( code, amount ) values ( 'A', 5 ); insert into #detail ( code, amount ) values ( 'A', 5 ); insert into #detail ( code, amount ) values ( 'B', 2 ); insert into #detail ( code, amount ) values ( 'B', 2 ); -- I would like to somehow simplify the following two queries insert into #head ( code, subtotal ) select code, sum(amount) from #detail group by code update #detail set head_id = h.head_id from #detail d inner join #head h on d.code = h.code -- This is the desired end result select * from #detail Desired end result of detail table: detail_id code amount head_id 1 A 5.00 1 2 A 5.00 1 3 B 2.00 2 4 B 2.00 2

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  • socket timeout and remove O_NONBLOCK option

    - by juxstapose
    Hello, I implemented a socket timeout and retry but in order to do it I had to set the socket as a non-blocking socket. However, I need the socket to block. This was my attempt at a solution to these two problems. This is not working. Subsequent send calls block but never send any data. When I connect without the select and the timeout, subsequent send calls work normally. References: C: socket connection timeout How to reset a socket back to blocking mode (after I set it to nonblocking mode)? Code: fd_set fdset; struct timeval tv; fcntl(dsock, F_SETFL, O_NONBLOCK); tv.tv_sec = theDeviceTimeout; tv.tv_usec = 0; int retries=0; logi(theLogOutput, LOG_INFO, "connecting to device socket num retrys: %i", theDeviceRetry); for(retries=0;retries<theDeviceRetry;retries++) { connect(dsock, (struct sockaddr *)&daddr, sizeof daddr); FD_ZERO(&fdset); FD_SET(dsock, &fdset); if (select(dsock + 1, NULL, &fdset, NULL, &tv) == 1) { int so_error; socklen_t slen = sizeof so_error; getsockopt(dsock, SOL_SOCKET, SO_ERROR, &so_error, &slen); if (so_error == 0) { logi(theLogOutput, LOG_INFO, "connected to socket on port %i on %s", theDevicePort, theDeviceIP); break; } else { logi(theLogOutput, LOG_WARN, "connect to %i failed on ip %s because %s retries %i", theDevicePort, theDeviceIP, strerror(errno), retries); logi(theLogOutput, LOG_WARN, "failed to connect to device %s", strerror(errno)); logi(theLogOutput, LOG_WARN, "error: %i %s", so_error, strerror(so_error)); continue; } } } int opts; opts = fcntl(dsock,F_GETFL); logi(theLogOutput, LOG_DEBUG, "clearing nonblock option %i retries %i", opts, retries); opts ^= O_NONBLOCK; fcntl(dsock, F_SETFL, opts);

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  • JPA/Hibernate Parent/Child relationship

    - by NubieJ
    Hi I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this): I have two entities: Parent and Child (naming changed). Parent contains a list of Children and Children refers back to parent. e.g. @Entity public class Parent { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "PARENT_ID", insertable = false, updatable = false) private int id; /* ..... */ @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true) private Set<child> children; /* ..... */ } @Entity public class Child { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "CHILD_ID", insertable = false, updatable = false) private int id; /* ..... */ @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID") private Parent parent; /* ..... */ } I want to be able to do the following: Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY. Retrieve a Child entity which would contain an instance of the Parent entity. Using the code above (or similar) results in two exceptions: Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML... Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id") Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId); return (Parent) query.getSingleResult(); } Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?

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  • Best way to get a random number from 1 to 50 which ISN'T x

    - by Cocorico
    Hi guys! So this is probably programming 101 stuff, but I have a problem: I have 2 numbers which are between 0 and 49. Let's call them x and y. Now I want to get a couple of other numbers which are not x or y, but are also between 0 and 49 (I am using Objective C but this is more of a general theory question I think?). Method I thought of is: int a; int b; int c; do { a = arc4random() % 49; } while ((a == x) || (a == y)); do { b = arc4random() % 49; } while ((b == x) || (b == y) || (b == a)); do { c = arc4random() % 49; } while ((c == x) || (c == y) || (c == a) || (c == b)); But it seem kind of bad to me, I don't know, I am just trying to learn to be a better programmer, what would be the most elegant sweet way to do this for best practices? Thanks!

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  • Linq2Sql: query - subquery optimisation

    - by Budda
    I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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  • Do all C compilers allow functions to return structures?

    - by Jordan S
    I am working on a program in C and using the SDCC compiler for a 8051 architecture device. I am trying to write a function called GetName that will read 8 characters from Flash Memory and return the character array in some form. I know that it is not possible to return an array in C so I am trying to do it using a struct like this: //********************FLASH.h file******************************* MyStruct GetName(int i); //Function prototype #define NAME_SIZE 8 typedef struct { char Name[NAME_SIZE]; } MyStruct; extern MyStruct GetName(int i); // *****************FLASH.c file*********************************** #include "FLASH.h" MyStruct GetName( int i) { MyStruct newNameStruct; //... // Fill the array by reading data from Flash //... return newNameStruct; } I don't have any references to this function yet but for some reason, I get a compiler error that says "Function cannot return aggregate." Does this mean that my compiler does not support functions that return structs? Or am I just doing something wrong?

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  • How can I modified the value of a string defined in a struc?

    - by Eric
    Hi, I have the following code in c++: define TAM 4000 define NUMPAGS 512 struct pagina { bitset<12 direccion; char operacion; char permiso; string *dato; int numero; }; void crearPagina(pagina* pag[], int pos, int dir) { pagina * paginas = (pagina*)malloc(sizeof(char) * TAM); paginas - direccion = bitset<12 (dir); paginas - operacion = 'n'; paginas - permiso = 'n'; string **tempDato = &paginas - dato; char *temp = " "; **tempDato = temp; paginas - numero = 0; pag[pos] = paginas; } I want to modify the value of the variable called "string *dato" in the struct pagina but, everytime I want to assing a new value, the compiler throws a segmentation fault. In this case I'm using a pointer to string, but I have also tried with a string. In a few words I want to do the following: pagina - dato = "test"; Any idea? Thanks in advance!!!

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  • How to get the size of a binary tree ?

    - by Andrei Ciobanu
    I have a very simple binary tree structure, something like: struct nmbintree_s { unsigned int size; int (*cmp)(const void *e1, const void *e2); void (*destructor)(void *data); nmbintree_node *root; }; struct nmbintree_node_s { void *data; struct nmbintree_node_s *right; struct nmbintree_node_s *left; }; Sometimes i need to extract a 'tree' from another and i need to get the size to the 'extracted tree' in order to update the size of the initial 'tree' . I was thinking on two approaches: 1) Using a recursive function, something like: unsigned int nmbintree_size(struct nmbintree_node* node) { if (node==NULL) { return(0); } return( nmbintree_size(node->left) + nmbintree_size(node->right) + 1 ); } 2) A preorder / inorder / postorder traversal done in an iterative way (using stack / queue) + counting the nodes. What approach do you think is more 'memory failure proof' / performant ? Any other suggestions / tips ? NOTE: I am probably going to use this implementation in the future for small projects of mine. So I don't want to unexpectedly fail :).

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  • cmd.exe Command Line Parsing of Environment Variables

    - by Artefacto
    I can't figure how to have cmd.exe not interpret something like %PATH% as an environment variable. Given this program: #include<stdio.h> #include<windows.h> int main(int argc, char *argv[]) { int i; printf("cmd line: %s\n", GetCommandLine()); for (i = 0; i < argc; i++) { printf("%d: %s\n", i, argv[i]); } return 0; } I have these different outputs according to the position of the arguments: >args "k\" o" "^%PATH^%" cmd line: args "k\" o" "%PATH%" 0: args 1: k" o 2: %PATH% >args "^%PATH^%" "k\" o" cmd line: args "^%PATH^%" "k\" o" 0: args 1: ^%PATH^% 2: k" o I guess it's because cmd.exe doesn't recognize the escaped \" and sees the escaped double quote as closing the first, leaving in the first case %PATH% unquoted. I say this, because if I don't quote the argument, it always works: >args ^%PATH^% "k\" o" cmd line: args %PATH% "k\" o" 0: args 1: %PATH% 2: k" o but then I can have no spaces...

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