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  • Use of 'super' keyword when accessing non-overridden superclass methods

    - by jonny
    I'm trying to get the hang of inheritance in Java and have learnt that when overriding methods (and hiding fields) in sub classes, they can still be accessed from the super class by using the 'super' keyword. What I want to know is, should the 'super' keyword be used for non-overridden methods? Is there any difference (for non-overridden methods / non-hidden fields)? I've put together an example below. public class Vehicle { public int tyreCost; public Vehicle(int tyreCost) { this.tyreCost = tyreCost; } public int getTyreCost() { return tyreCost; } } and public class Car extends Vehicle { public int wheelCount; public Vehicle(int tyreCost, int wheelCount) { super(tyreCost); this.wheelCount = wheelCount; } public int getTotalTyreReplacementCost() { return getTyreCost() * wheelCount; } } Specifically, given that getTyreCost() hasn't been overridden, should getTotalTyreReplacementCost() use getTyreCost(), or super.getTyreCost() ? I'm wondering whether super should be used in all instances where fields or methods of the superclass are accessed (to show in the code that you are accessing the superclass), or only in the overridden/hidden ones (so they stand out).

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  • How to refresh/redraw the screen (not the program window)

    - by mohrphium
    I'm having a bit of a hard time figuring out, how to remove a drawn ellipse after it has been drawn somewhere else. I need a circle to follow my mouse all the time and this is all the program should do. I get the mousepositions and draw my circle but how can I remove the last one? #include <Windows.h> #include <iostream> void drawRect(int a1, int a2){ HDC screenDC = ::GetDC(0); //Draw circle at mouse position ::Ellipse(screenDC, a1, a2+5, a1+9, a2+14); ::ReleaseDC(0, screenDC); //::InvalidateRect(0, NULL, TRUE); //<- I tried that but then everything flickers //Also, the refresh rate is not fast enough... still some circles left } int main(void) { int a1; int a2; bool exit=false; while (exit!=true) { POINT cursorPos; GetCursorPos(&cursorPos); float x = 0; x = cursorPos.x; float y = 0; y = cursorPos.y; a1=(int)cursorPos.x; a2=(int)cursorPos.y; drawRect(a1, a2); } } I am working with graphics and all that stuff for the first time. Im kinda stuck here... once again. Thanks.

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  • Circle to move when mouse clicked Java

    - by Myt
    So I am really new to Java and I need a circle to move around JFrame when it's clicked, but the circle has to get random cordinates. So far this code generates a new circle every time it's clicked, but all the other circles stay there aswell, but I only need one circle to move around the frame. So maybe someone can help me a little :) public class test2 extends JFrame implements MouseListener { int height, width; public test2() { this.setTitle("Click"); this.setSize(400,400); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setVisible(true); addMouseListener(this); width = getSize().width; height = getSize().height; } public void paint (Graphics g) { setBackground (Color.red); g.setColor(Color.yellow); int a, b; a = -50 + (int)(Math.random()*(width+40)); b = (int)(Math.random()*(height+20)); g.fillOval(a, b, 130, 110); } public void mouseClicked(MouseEvent e) { int a, b; a = -50 + (int)(Math.random()*(width+40)); b = (int)(Math.random()*(height+20)); repaint(); } public void mouseReleased(MouseEvent e){} public void mouseEntered(MouseEvent e){} public void mouseExited(MouseEvent e){} public void mousePressed(MouseEvent e){} public static void main(String arg[]){ new test2(); } }

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  • Go and a bad prime number algorithm

    - by anonymous
    I wrote this prime number sieving algorithm and it doesn't run properly. I can't find the error in the algorithm itself. Could someone help me? This is what it's supposed to print: [2 3 5 7 11 13 17 19 23 29] Versus what it actually prints: [3 5 7 11 13 17 19 23 25 29] . package main import "fmt" func main() { var primes = sieve(makeNumbers(29)) fmt.Printf("%d\n", primes); } func makeNumbers(n int) []int { var numbers = make([]int, n - 1) for i := 0; i < len(numbers); i++ { numbers[i] = i + 2 } return numbers } func sieve(numbers []int) []int { var numCopy = numbers var max = numbers[len(numbers)-1] var sievedNumbers = make([]int, 0) for i := 0; numCopy[i]*numCopy[i] <= max; i++ { for j := i; j < len(numCopy); j++ { if numCopy[j] % numCopy[i] != 0 || j == i { sievedNumbers = append(sievedNumbers, numCopy[j]) } } numCopy = sievedNumbers sievedNumbers = make([]int, 0) } return numCopy }

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  • scanf a byte then print it out?

    - by Sarah
    I've searched around to see if I can find this answer but I can't seem to (please let me know if I'm wrong). I am trying to use scanf to read in a byte, an unsigned int and a char in one .c file and I am trying to access this byte in a different .c file and print it out. (I have already checked to make sure I have included all the appropriate parameters everywhere) But I keep getting errors. The warnings are: database.c: In function ‘addCitizen’: database.c:23:2: warning: format ‘%hhu’ expects argument of type ‘int’, but argument 2 has type ‘byte *’ [-Wformat] database.c:24:2: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 2 has type ‘int *’ [-Wformat] database.c:25:2: warning: format ‘%c’ expects argument of type ‘int’, but argument 2 has type ‘char *’ [-Wformat] where I'm scanf'ing: // Request loop while (count-- != 0) { while (1){ // Get values from the user int error = scanf ("%79s %hhu %u %c", tname, &tdist, &tyear, &tgender); addCitizen(db, tname, &tdist, &tyear, &tgender); where I'm printing: void addCitizen(Database *db, char *tname, byte *tdist, int *tyear, char *tgender){ //needs to find the right place in memory to put this stuff and then put it there printf("\nName is: %79s\n", tname); printf("District is: %hhu\n", tdist); printf("Year of birth is: %u\n", tyear); printf("Gender is:%c\n", tgender); I'm not sure where I'm going wrong?

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  • Why am I getting a ClassCastException here?

    - by Holly
    I'm creating an android application and i'm trying to use a PreferenceActivity. I'm getting the java.lang.ClassCastException: java.lang.String error when it gets to this line return PreferenceManager.getDefaultSharedPreferences(context).getInt(USER_TERM, USER_TERM_DEF); I thought it might be because I'm not converting it properly from it's string value in the EditText box to the int I need but I can't figure out how to fix this, or is that even the cause? I'm flummoxed. Here's my preference activity class: public class UserPrefs extends PreferenceActivity { //option names and default vals private static final String USER_TERM = "term_length"; private static final String USER_YEAR = "year_length"; private static final int USER_TERM_DEF = 12; private static final int USER_YEAR_DEF = 34; @Override protected void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.preferences); } public static int getTermLength(Context context){ try{ return PreferenceManager.getDefaultSharedPreferences(context).getInt(USER_TERM, USER_TERM_DEF); }catch (ClassCastException e){Log.v("getTermLength", "error::: " + e); } //return 1;//temporary, needed to catch the error and couldn't without adding a return outside the block.// } public static int getYearLength(Context context){ return PreferenceManager.getDefaultSharedPreferences(context).getInt(USER_YEAR, USER_YEAR_DEF); } And here's the bit of code where I'm trying to use the the preferences inside another class: public float alterForFrequency(Context keypadContext, float enteredAmount, String spinnerPosition){ int termLength = UserPrefs.getTermLength(keypadContext); int yearLength = UserPrefs.getYearLength(keypadContext); } The complete android logcat, i've uploaded here: http://freetexthost.com/v3t4ta3wbi

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  • C# Recursion SumOfOnlyNeg Elements

    - by Chris
    Hello, A array gets filled up with random elements (negative and positive). Now i want to calculate the sum of ONLY the postive elements. Iterative there is no problem, but in the recursion version i can only get the sum of both negative and postive. How can i "check" in the recursive version that it only sums up the Postive elements? Best Regards. Iterative version: public int IterSomPosElem(int[] tabel, int n) { n = 0; for (int i = 0; i < tabel.Length; i++) { if (tabel[i] >= 0) { n += tabel[i]; } } return n; } Recursive version atm (sums up all the elements insteed, of only the positive) public int RecuSomPosElem(int[] tabel, int n) { if(n == 1) return tabel[0]; //stopCriterium else { return (tabel[n - 1] + RecuSomPosElem(tabel, n - 1)); // how to check, so it only sums up the postive elements and "ignores" the negative elements. } }

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  • querying huge database table takes too much of time in mysql

    - by Vijay
    Hi all, I am running sql queries on a mysql db table that has 110Mn+ unique records for whole day. Problem: Whenever I run any query with "where" clause it takes at least 30-40 mins. Since I want to generate most of data on the next day, I need access to whole db table. Could you please guide me to optimize / restructure the deployment model? Site description: mysql Ver 14.12 Distrib 5.0.24, for pc-linux-gnu (i686) using readline 5.0 4 GB RAM, Dual Core dual CPU 3GHz RHEL 3 my.cnf contents : [root@reports root]# cat /etc/my.cnf [mysqld] datadir=/data/mysql/data/ socket=/tmp/mysql.sock sort_buffer_size = 2000000 table_cache = 1024 key_buffer = 128M myisam_sort_buffer_size = 64M # Default to using old password format for compatibility with mysql 3.x # clients (those using the mysqlclient10 compatibility package). old_passwords=1 [mysql.server] user=mysql basedir=/data/mysql/data/ [mysqld_safe] err-log=/data/mysql/data/mysqld.log pid-file=/data/mysql/data/mysqld.pid [root@reports root]# DB table details: CREATE TABLE `RAW_LOG_20100504` ( `DT` date default NULL, `GATEWAY` varchar(15) default NULL, `USER` bigint(12) default NULL, `CACHE` varchar(12) default NULL, `TIMESTAMP` varchar(30) default NULL, `URL` varchar(60) default NULL, `VERSION` varchar(6) default NULL, `PROTOCOL` varchar(6) default NULL, `WEB_STATUS` int(5) default NULL, `BYTES_RETURNED` int(10) default NULL, `RTT` int(5) default NULL, `UA` varchar(100) default NULL, `REQ_SIZE` int(6) default NULL, `CONTENT_TYPE` varchar(50) default NULL, `CUST_TYPE` int(1) default NULL, `DEL_STATUS_DEVICE` int(1) default NULL, `IP` varchar(16) default NULL, `CP_FLAG` int(1) default NULL, `USER_LOCATE` bigint(15) default NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 MAX_ROWS=200000000; Thanks in advance! Regards,

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  • Mono & DeflateStream

    - by ILya
    I have a simple code byte[] buffer = Encoding.UTF8.GetBytes("abracadabra"); MemoryStream ms = new MemoryStream(); DeflateStream ds = new DeflateStream(ms, CompressionMode.Compress, false); ms.Write(buffer, 0, buffer.Length); DeflateStream ds2 = new DeflateStream(ms, CompressionMode.Decompress, false); byte[] buffer2 = new byte[ms.Length]; ds2.Read(buffer2, 0, (int)ms.Length); Console.WriteLine(Encoding.UTF8.GetString(buffer2)); And when reading from ds2, i have the following: Stacktrace: at (wrapper managed-to-native) System.IO.Compression.DeflateStream.ReadZStream (intptr,intptr,int) <0x00004 at (wrapper managed-to-native) System.IO.Compression.DeflateStream.ReadZStream (intptr,intptr,int) <0x00004 at System.IO.Compression.DeflateStream.ReadInternal (byte[],int,int) [0x00031] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.6.3\mcs\class\System\System.IO.Compression\DeflateStream.cs:192 at System.IO.Compression.DeflateStream.Read (byte[],int,int) [0x00086] in C:\cygwin\tmp\monobuild\build\BUILD\mono-2.6.3\mcs\class\System\System.IO.Compression\DeflateStream.cs:214 at testtesttest.MainClass.Main (string[]) [0x00041] in C:\Users\ilukyanov\Desktop\Cassini\GZipDemo\Main.cs:27 at (wrapper runtime-invoke) .runtime_invoke_void_object (object,intptr,intptr,intptr) This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. This problem appears in Mono 2.6.1 & 2.6.3... Is there any known way to successfully read from DeflateStream in Mono? Or maybe there are some third-party open-source assemblies with the same functionality?

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  • Is it possible to De-Serialize a new Derived class using Old Binary?

    - by Anand
    In my project I have a class which I Serialize in Binary format to the disk. Due to some new requirement I need to create a new class which is derived from the original class. eg [Serializable] public class Sample { String someString; int someInt; public Sample() { } public Sample(String _someString, int _someInt) { this.someInt = _someInt; this.someString = _someString; } public String SomeString { get { return someString; } } public int SomeInt { get { return someInt; } } } [Serializable] public class DerivedSample : Sample { String someMoreString; int someMoreInt; public DerivedSample () : base() { } public DerivedSample (String _someString, int _someInt, String _someMoreString, int _someMoreInt) : base(_someString, _someInt) { this.someMoreString = _someMoreString; this.someMoreInt = _someMoreInt; } public String SomeMoreString { get { return someMoreString; } } public int SomeMoreInt { get { return someMoreInt; } } } When I try to De serialize an old file which contains only object of Sample it works fine, in the current assembly. That means backward compatibility is there. But when I try to deserialize the file which contains object of DerivedSample using the previous version of the assembly application crashes. Which means forward compatibilty needs to be taken care off... It it possible to say read only the base class part of the object from new version of the file?

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  • Argument type deduction, references and rvalues

    - by uj2
    Consider the situation where a function template needs to forward an argument while keeping it's lvalue-ness in case it's a non-const lvalue, but is itself agnostic to what the argument actually is, as in: template <typename T> void target(T&) { cout << "non-const lvalue"; } template <typename T> void target(const T&) { cout << "const lvalue or rvalue"; } template <typename T> void forward(T& x) { target(x); } When x is an rvalue, instead of T being deduced to a constant type, it gives an error: int x = 0; const int y = 0; forward(x); // T = int forward(y); // T = const int forward(0); // Hopefully, T = const int, but actually an error forward<const int>(0); // Works, T = const int It seems that for forward to handle rvalues (without calling for explicit template arguments) there needs to be an forward(const T&) overload, even though it's body would be an exact duplicate. Is there any way to avoid this duplication?

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  • Entity and N-Tier architecture in C#

    - by acadia
    Hello, I have three tables as shown below Emp ---- empID int empName deptID empDetails ----------- empDetailsID int empID int empDocuments -------------- docID empID docName docType I am creating a entity class so that I can use n-tier architecture to do database transactions etc in C#. I started creating class for the same as shown below using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace employee { class emp { private int empID; private string empName; private int deptID; public int EmpID { get; set; } public string EmpName { get; set; } public int deptID { get; set; } } } My question is as empDetails and empDocuments are related to emp by empID. How do I have those in my emp class. I would appreciate if you can direct me to an example. Thanks

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  • Using deprecated binders and C++0x lambdas

    - by Sumant
    C++0x has deprecated the use of old binders such as bind1st and bind2nd in favor of generic std::bind. C++0x lambdas bind nicely with std::bind but they don't bind with classic bind1st and bind2nd because by default lambdas don't have nested typedefs such as argument_type, first_argument_type, second_argument_type, and result_type. So I thought std::function can serve as a standard way to bind lambdas to the old binders because it exposes the necessary typedefs. However, using std::function is hard to use in this context because it forces you to spell out the function-type while instantiating it. auto bound = std::bind1st(std::function<int (int, int)>([](int i, int j){ return i < j; }), 10); // hard to use auto bound = std::bind1st(std::make_function([](int i, int j){ return i < j; }), 10); // nice to have but does not compile. I could not find a convenient object generator for std::function. Something like std::make_fuction would be nice to have. Does such a thing exist? If not, is there any other better way of binding lamdas to the classic binders?

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  • retrieve image from gallery in android

    - by smsys
    I have created an Activity where i have a Button. By pressing the button an android Gallery opens. When i choose an image from the gallery it is shows it in an ImageView of my Activity but after choosing second time the following error occuring 01-13 17:55:25.323: ERROR/AndroidRuntime(14899): java.lang.OutOfMemoryError: bitmap size exceeds VM budget Here is the source code i am using: public class MyImage extends Activity { /** Called when the activity is first created. */ Gallery gallery; private Uri[] mUrls; String[] mFiles=null; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); File images = Environment.getDataDirectory(); File[] imagelist = images.listFiles(); mFiles = new String[imagelist.length]; for(int i= 0 ; i< imagelist.length; i++) { mFiles[i] = imagelist[i].getAbsolutePath(); } mUrls = new Uri[mFiles.length]; for(int i=0; i < mFiles.length; i++) { mUrls[i] = Uri.parse(mFiles[i]); } Gallery g = (Gallery) findViewById(R.id.Gallery01); g.setAdapter(new ImageAdapter(this)); g.setFadingEdgeLength(40); } public class ImageAdapter extends BaseAdapter{ int mGalleryItemBackground; public ImageAdapter(Context c) { mContext = c; } public int getCount(){ return mUrls.length; } public Object getItem(int position){ return position; } public long getItemId(int position) { return position; } public View getView(int position, View convertView, ViewGroup parent){ ImageView i = new ImageView(mContext); i.setImageURI(mUrls[position]); i.setScaleType(ImageView.ScaleType.FIT_XY); i.setLayoutParams(new Gallery.LayoutParams(260, 210)); return i; } private Context mContext; } }

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  • Loading data from file to Vector structure

    - by owca
    I'm trying to parse through fixed-width formatted file extracting x,y values of points from it, and then storing them in int[] array inside a Vector. Text file looks as follows : 0006 0015 0125 0047 0250 0131 That's the code : Vector<int[]> vc = new Vector<int[]>(); try { BufferedReader file = new BufferedReader(new FileReader("myfile.txt")); String s; int[] vec = new int[2]; while ((s = file.readLine()) != null) { vec[0] = Integer.parseInt(s.substring(0, 4).trim()); vec[1] = Integer.parseInt(s.substring(5, 8).trim()); vc.add(vec); } file.close(); } catch (IOException e) { } for(int i=0; i<vc.size(); i++){ for(int j=0; j<2; j++){ System.out.println(vc.elementAt(i)[j]); } } But the output shows only last line. 250 131 250 131 250 131 Should I somehow use Vector.nextElement() here to get all my data ?

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  • passing multidimensional arrays to function

    - by Pegah
    hi! I have a method in my class which uses a 3dimensional tfpairexp as input parameter. and I need to use the values in tfpairexp later. void calctfpairexp (int tf1, int tf2, double tfpairexp[][2][3]) { int ctr,c; for (int j = 0; j < cchips && (c = chips[j].crepls); j += c) { int ctrl_no=0; for (int *p = chips[j].ctrl ; p && (ctr=*p)>=0; ++p,ctrl_no++) { for (int k = 0; k < c; ++k) { tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); } } } } I call the method inside the class like this: calctfpairexp(tf1,tf2,tfpairexp); and I need to use values inside tfpairexp in next lines. but the compiler gives error in this line: tfpairexp[j][ctrl_no][k]=interactionFunc(2,3,1); and says that the tfpairexp variable is not defined in the calctfpairexp function. any idea?

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  • clang does not compile but g++ does

    - by user1095108
    Can someone help me with this code: #include <type_traits> #include <vector> struct nonsense { }; template <struct nonsense const* ptr, typename R> typename std::enable_if<!std::is_void<R>::value, int>::type fo(void* const) { return 0; } template <struct nonsense const* ptr, typename R> typename std::enable_if<std::is_void<R>::value, int>::type fo(void* const) { return 1; } typedef int (*func_type)(void*); template <std::size_t O> void run_me() { static struct nonsense data; typedef std::pair<char const* const, func_type> pair_type; std::vector<pair_type> v; v.push_back(pair_type{ "a", fo<&data, int> }); v.push_back(pair_type{ "b", fo<&data, void> }); } int main(int, char*[]) { run_me<2>(); return 0; } clang-3.3 does not compile this code, but g++-4.8.1 does, which of the two compiler is right? Is something wrong with the code, as I suspect? The error reads: a.cpp:32:15: error: no matching constructor for initialization of 'pair_type' (aka 'pair<const char *const, func_type>') v.push_back(pair_type{ "a", fo<&data, int> }); ^ ~~~~~~~~~~~~~~~~~~~~~~~ a.cpp:33:15: error: no matching constructor for initialization of 'pair_type' (aka 'pair<const char *const, func_type>') v.push_back(pair_type{ "b", fo<&data, void> }); ^ ~~~~~~~~~~~~~~~~~~~~~~~~

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  • Using an empty column as a divider in a JTable.

    - by Catalina Island
    I'm trying to use an empty column as a divider between pairs of columns in a JTable. Here's a picture and code for what I have so far. I know I can change the look using a custom TableCellRenderer. Before I go down that road, is there a better way to do this? Any ideas appreciated. import javax.swing.*; import javax.swing.table.*; public class TablePanel extends JPanel { public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { JFrame f = new JFrame("TablePanel"); f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); f.add(new TablePanel()); f.pack(); f.setVisible(true); } }); } public TablePanel() { TableModel dataModel = new MyModel(); JTable table = new JTable(dataModel); table.getColumnModel().getColumn(MyModel.DIVIDER).setMaxWidth(0); JScrollPane jsp = new JScrollPane(table); jsp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS); this.add(jsp); } private static class MyModel extends AbstractTableModel { private static final int DIVIDER = 2; private final String[] names = { "A1", "A2", "", "B1", "B2" }; @Override public int getRowCount() { return 32; } @Override public int getColumnCount() { return names.length; } @Override public String getColumnName(int col) { if (col == DIVIDER) return ""; return names[col]; } @Override public Object getValueAt(int row, int col) { if (col == DIVIDER) return ""; return (row + 1) / 10.0; } @Override public Class<?> getColumnClass(int col) { if (col == DIVIDER) return String.class; return Number.class; } } }

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  • Visual C++ 2010, rvalue reference bug?

    - by Sergey Shandar
    Is it a bug in Visual C++ 2010 or right behaviour? template<class T> T f(T const &r) { return r; } template<class T> T f(T &&r) { static_assert(false, "no way"); return r; } int main() { int y = 4; f(y); } I thought, the function f(T &&) should never be called but it's called with T = int &. The output: main.cpp(10): error C2338: no way main.cpp(17) : see reference to function template instantiation 'T f<int&>(T)' being compiled with [ T=int & ] Update 1 Do you know any C++x0 compiler as a reference? I've tried comeau online test-drive but could not compile r-value reference. Update 2 Workaround (using SFINAE): #include <boost/utility/enable_if.hpp> #include <boost/type_traits/is_reference.hpp> template<class T> T f(T &r) { return r; } template<class T> typename ::boost::disable_if< ::boost::is_reference<T>, T>::type f(T &&r) { static_assert(false, "no way"); return r; } int main() { int y = 4; f(y); // f(5); // generates "no way" error, as expected. }

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  • How can i create an n-dimensional array in c

    - by shortCircuit
    I was thinking of making a function that would accept the size of array as a parameter and create a n dimensional array. My room-mate took the liberty of making it complex. He said lets write a function that takes n parameters and returns an n-dimensional array using those parameters as the dimensions. Now i realize an one-day and d array is easy to implement with pointers. For 2d array the snippet would be something like (standard way) : int** x; int* temp; x = (int**)malloc(m * sizeof(int*)); temp = (int*)malloc(m*n * sizeof(int)); for (int i = 0; i < m; i++) { x[i] = temp + (i * n); } where the array is of size m*n; But the problem lies how do we find the nested loop parameters for a n-dimensional array? Is there any way to optimize the code?

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  • SELECT product from subclass: How many queries do I need?

    - by Stefano
    I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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  • Why won't this work; opencv Mat_<float>

    - by user1371674
    I can't seem to get this to work. I'm trying to get the pixel value of an image but first need to change the color of the image, but since I cannot use int or just Mat because the values are not whole numbers, I have to use and because of that errors pop up when I try to run this on the cmd. int main(int argc, char **argv) { Mat img = imread(argv[1]); ofstream myfile; Mat_<float> MatBlue = img; int rows1 = MatBlue.rows; int cols1 = MatBlue.cols; for(int x = 0; x < cols1; x++) { for(int y = 0; y < rows1; y++) { float val = MatBlue.at<cv::Vec3b>(y, x)[1]; MatBlue.at<cv::Vec3b>(y, x)[0] = val + 1; } } }

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  • Need help in Hashtable implementation

    - by rafael
    Hi all, i'm quite a beginner in C# , i tried to write a program that extract words from an entered string, the user has to enter a minimum length for the word to filter the words output ... my code doesn't look good or intuitive, i used two arrays countStr to store words , countArr to store word length corresponding to each word .. but the problem is i need to use hashtables instead of those two arrays , because both of their sizes are depending on the string length that the user enter , i think that's not too safe for the memory or something ? here's my humble code , again i'm trying to replace those two arrays with one hashtable , how can this be done ? using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Collections; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { int i = 0 ; int j = 0; string myString = ""; int counter = 0; int detCounter = 0; myString = Console.ReadLine(); string[] countStr = new string[myString.Length]; int[] countArr = new int[myString.Length]; Console.Write("Enter minimum word length:"); detCounter = int.Parse(Console.ReadLine()); for (i = 0; i < myString.Length; i++) { if (myString[i] != ' ') { counter++; countStr[j] += myString[i]; } else { countArr[j] = counter; counter = 0; j++; } } if (i == myString.Length) { countArr[j] = counter; } for (i = 0; i < myString.Length ; i++) { if (detCounter <= countArr[i]) { Console.WriteLine(countStr[i]); } } Console.ReadLine(); } } }

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  • C struct written in file, open with Java

    - by DaunnC
    For example in C I have structure: typedef struct { int number; double x1; double y1; double x2; double y2; double x3; double y3; } CTRstruct;` Then I write it to file fwrite(&tr, 1, sizeof(tr), fp); (tr - its CTRstruct var, fp - File pointer); Then I need to read it with Java! I really don't know how to read struct from file... I tried to read it with ObjectInputStream(), last idea is to read with RandomAccessFile() but I also don't know how to... (readLong(), readDouble() also doesn't work, it works ofcource but doesn't read correct data). So, any idea how to read C struct from binary file with Java? If it's interesting, my version to read integer (but it's ugly, & I don't know what to do with double): public class MyDataInputStream extends DataInputStream{ public MyDataInputStream(InputStream AIs) { super(AIs); } public int readInt1() throws IOException{ int ch1 = in.read(); int ch2 = in.read(); int ch3 = in.read(); int ch4 = in.read(); if ((ch1 | ch2 | ch3 | ch4) < 0) throw new EOFException(); return ((ch4 << 24) + (ch3 << 16) + (ch2 << 8) + (ch1 << 0)); } with double we can deal the same way (like with int or with long (8bytes) & then convert to double with native func).

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  • whether rand_r is real thread safe?

    - by terry
    Well, rand_r function is supposed to be a thread safe function. However, by its implementation, I cannot believe it could make itself not change by other threads. Suppose that two threads will invoke rand_r in the same time with the same variable seed. So read-write race will occur. The code rand_r implemented by glibc is listed below. Anybody knows why rand_r is called thread safe? int rand_r (unsigned int *seed) { unsigned int next = *seed; int result; next *= 1103515245; next += 12345; result = (unsigned int) (next / 65536) % 2048; next *= 1103515245; next += 12345; result <<= 10; result ^= (unsigned int) (next / 65536) % 1024; next *= 1103515245; next += 12345; result <<= 10; result ^= (unsigned int) (next / 65536) % 1024; *seed = next; return result; }

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