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  • What are pointers to class members used for?

    - by srikfreak
    I have read about pointers to class members, but I have never seen them being used in any practical applications. Can someone explain what are the use cases of such pointers? Is it really necessary to have such pointers? Eg. class abc { public: int a; abc(int val) { a = val; } }; int main { int abc::*data; abc obj(5); data = &abc::a; cout << "Value of a is " << obj.*data << endl; return 0; } In the above eg. why is the value of 'a' accessed in this manner? What is the advantage of using pointers to class members?

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  • How use asp.net get video duration

    - by mhmt
    using Microsoft.DirectX.AudioVideoPlayback; Video vvideo = new Video(FileUpload.FileName.ToString()); StringBuilder sb = new StringBuilder(); sb.Append(duration.toString()); error message; “Installed an access attempt was made to the application domain.” “vvideo” instance is created error msj :// But down found cods I found a working code in c #. but asp.net does not work string file1 = "c://ds.mpeg" IMediaPosition m_objMediaPosition = null; FilgraphManager m_objFilterGraph = new FilgraphManager(); m_objFilterGraph.RenderFile(filename); m_objMediaPosition = m_objFilterGraph as IMediaPosition; int s = (int)m_objMediaPosition.Duration; int h = s / 3600; int m = (s - (h * 3600)) / 60; s = s - (h * 3600 + m * 60); I DON'T TAKE VIDEO DURATION BOYS :/

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  • How to design a class for managing file path ?

    - by remi bourgarel
    Hi All In my app, I generate some xml file for instance : "/xml/product/123.xml" where 123 is the product's id and 123.xml contains informations about this product. I also have "/xml/customer/123.xml" where 123.xml contains informations about the client ... 123 How can I manage these file paths : 1/ - I create the file path directly in the seralization method ? 2/ I create 2 static class : CustomerSerializationPathManager and ProductSerializationPathManager with 1 method : getPath(int customerID) and getPath(int productID) 3/ I create one static class : SerializationPathManager with 2 method : getCustomerPath(int customerID) and getProductPath(int productID) 4/ something else I'd prefer the solution 3 cause if I think there's only one reason to change this class : I change the root directory. So I'd like to have your thoughts about it... thx

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  • how to implement OOP using QT

    - by kaycee
    hi, this is a simple OOP QT question. my app consists of main window (QMainWindow) and a table (QTableWidget). in the main window i have arguments and variables which i would like to pass to the table class, and to access methods in main widnow class from the table class, how should i do it ? mainwindow.h class MainWindow : public QMainWindow { Q_OBJECT private: int a; int b; Spreadsheet *spreadsheet; public: void set_a(int); void set_b(int); spreadsheet.h class Spreadsheet : public QTableWidget { Q_OBJECT public: Spreadsheet(QWidget *parent = 0); atm i define Spreadsheet like this: spreadsheet = new Spreadsheet(this); and i'd like to access set_a() from spreadsheet.cpp...

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  • C++ non-member functions for nested template classes

    - by beldaz
    I have been writing several class templates that contain nested iterator classes, for which an equality comparison is required. As I believe is fairly typical, the comparison is performed with a non-member (and non-friend) operator== function. In doing so, my compiler (I'm using Mingw32 GCC 4.4 with flags -O3 -g -Wall) fails to find the function and I have run out of possible reasons. In the rather large block of code below there are three classes: a Base class, a Composed class that holds a Base object, and a Nested class identical to the Composed class except that it is nested within an Outer class. Non-member operator== functions are supplied for each. These classes are in templated and untemplated forms (in their own respective namespaces), with the latter equivalent to the former specialised for unsigned integers. In main, two identical objects for each class are compared. For the untemplated case there is no problem, but for the templated case the compiler fails to find operator==. What's going on? #include <iostream> namespace templated { template<typename T> class Base { T t_; public: explicit Base(const T& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; template<typename T> bool operator==(const Base<T> &x, const Base<T> &y) { return x.equal(y); } template<typename T> class Composed { typedef Base<T> Base_; Base_ base_; public: explicit Composed(const T& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; template<typename T> bool operator==(const Composed<T> &x, const Composed<T> &y) { return x.equal(y); } template<typename T> class Outer { public: class Nested { typedef Base<T> Base_; Base_ base_; public: explicit Nested(const T& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; template<typename T> bool operator==(const typename Outer<T>::Nested &x, const typename Outer<T>::Nested &y) { return x.equal(y); } } // namespace templated namespace untemplated { class Base { unsigned int t_; public: explicit Base(const unsigned int& t) : t_(t) {} bool equal(const Base& x) const { return x.t_==t_; } }; bool operator==(const Base &x, const Base &y) { return x.equal(y); } class Composed { typedef Base Base_; Base_ base_; public: explicit Composed(const unsigned int& t) : base_(t) {} bool equal(const Composed& x) const {return x.base_==base_;} }; bool operator==(const Composed &x, const Composed &y) { return x.equal(y); } class Outer { public: class Nested { typedef Base Base_; Base_ base_; public: explicit Nested(const unsigned int& t) : base_(t) {} bool equal(const Nested& x) const {return x.base_==base_;} }; }; bool operator==(const Outer::Nested &x, const Outer::Nested &y) { return x.equal(y); } } // namespace untemplated int main() { using std::cout; unsigned int testVal=3; { // No templates first typedef untemplated::Base Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Composed Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "c==d ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef untemplated::Outer::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; } { // Now with templates typedef templated::Base<unsigned int> Base_t; Base_t a(testVal); Base_t b(testVal); cout << "a=b=" << testVal << "\n"; cout << "a==b ? " << (a==b ? "TRUE" : "FALSE") << "\n"; typedef templated::Composed<unsigned int> Composed_t; Composed_t c(testVal); Composed_t d(testVal); cout << "c=d=" << testVal << "\n"; cout << "d==c ? " << (c==d ? "TRUE" : "FALSE") << "\n"; typedef templated::Outer<unsigned int>::Nested Nested_t; Nested_t e(testVal); Nested_t f(testVal); cout << "e=f=" << testVal << "\n"; cout << "e==f ? " << (e==f ? "TRUE" : "FALSE") << "\n"; // Above line causes compiler error: // error: no match for 'operator==' in 'e == f' } cout << std::endl; return 0; }

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  • Dynamically change ViewPagerIndicator titles

    - by msal
    My current project uses some ListFragments to show rows of data. The rows get updated dynamically every some seconds. The amount of rows varies with every update and in every ListFragment. I would like to show the amount of rows to the user, and think that the perfect place for that would be next to the Fragment's title in the ViewPagerIndicator. I provided a sample image for better comprehension: Sadly I am pretty clueless how to achieve this. I tried the following: public class PagerAdapter extends FragmentPagerAdapter { private int numOne = 0; private int numTwo = 0; // ... @Override public CharSequence getPageTitle(int position) { switch (position) { case 0: return "List 1 (" + numOne + ")"; case 1: return "List 2 (" + numTwo + ")"; default: return ""; } public void setNumOne(int num) { this.numOne = num; } public void setNumTwo(int num) { this.numTwo = num; } } When I now call the setNumXXX() method, nothing happens, until I move between fragments, what seems to trigger the getPageTitle() to fire. My question is: How can I force an update of the title(s), everytime when the num value changes?

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  • Insert MANY key value pairs fast into berkeley db with hash access

    - by Kungi
    Hi, i'm trying to build a hash with berkeley db, which shall contain many tuples (approx 18GB of key value pairs), but in all my tests the performance of the insert operations degrades drastically over time. I've written this script to test the performance: #include<iostream> #include<db_cxx.h> #include<ctime> #define MILLION 1000000 int main () { long long a = 0; long long b = 0; int passes = 0; int i = 0; u_int32_t flags = DB_CREATE; Db* dbp = new Db(NULL,0); dbp->set_cachesize( 0, 1024 * 1024 * 1024, 1 ); int ret = dbp->open( NULL, "test.db", NULL, DB_HASH, flags, 0); time_t time1 = time(NULL); while ( passes < 100 ) { while( i < MILLION ) { Dbt key( &a, sizeof(long long) ); Dbt data( &b, sizeof(long long) ); dbp->put( NULL, &key, &data, 0); a++; b++; i++; } DbEnv* dbep = dbp->get_env(); int tmp; dbep->memp_trickle( 50, &tmp ); i=0; passes++; std::cout << "Inserted one million --> pass: " << passes << " took: " << time(NULL) - time1 << "sec" << std::endl; time1 = time(NULL); } } Perhaps you can tell me why after some time the "put" operation takes increasingly longer and maybe how to fix this. Thanks for your help, Andreas

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  • What's the difference between an option type and a nullable type?

    - by Peter Olson
    In F# mantra there seems to be a visceral avoidance of null, Nullable<T> and its ilk. In exchange, we are supposed to instead use option types. To be honest, I don't really see the difference. My understanding of the F# option type is that it allows you to specify a type which can contain any of its normal values, or None. For example, an Option<int> allows all of the values that an int can have, in addition to None. My understanding of the C# nullable types is that it allows you to specify a type which can contain any of its normal values, or null. For example, a Nullable<int> a.k.a int? allows all of the values that an int can have, in addition to null. What's the difference? Do some vocabulary replacement with Nullable and Option, null and None, and you basically have the same thing. What's all the fuss over null about?

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  • Am I doing getters/setters the right way in Java?

    - by Sergio Tapia
    public class Persona { int Codigo; String Nombre; public Persona(int Codigo, String Nombre){ this.Codigo = Codigo; this.Nombre = Nombre; } public void setCodigo(int Codigo){ this.Codigo = Codigo; } public int getCodigo(){ return this.Codigo; } public void setNombre(String Nombre){ this.Nombre = Nombre; } public String getNombre(){ return this.Nombre; } } Or is there a much shorter (realiable) way to do it?

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  • What makes this struct incomplete?

    - by Mechko
    gcc lovingly throws me this error: bst.c:33: error: invalid application of ‘sizeof’ to incomplete type ‘struct BSTNode’ What makes BSTnode incomplete? Below are the struct definitions relevant to BSTnode. struct BSTnode{ struct BSTnode * left; struct BSTnode * right; struct hash minhash; struct hash maxhash; struct DHTid owner; int misses; }; where we have: struct hash{ int hash; } struct DHTid { int islocal; unsigned long addr; unsigned short port; struct DHTnode * node; }; and currently: struct DHTnode{ int something; }

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  • Dynamic memory inside a struct

    - by Maximilien
    Hello, I'm editing a piece of code, that is part of a big project, that uses "const's" to initialize a bunch of arrays. Because I want to parametrize these const's I have to adapt the code to use "malloc" in order to allocate the memory. Unfortunately there is a problem with structs: I'm not able to allocate dynamic memory in the struct itself. Doing it outside would cause to much modification of the original code. Here's a small example: int globalx,globaly; struct bigStruct{ struct subStruct{ double info1; double info2; bool valid; }; double data; //subStruct bar[globalx][globaly]; subStruct ** bar=(subStruct**)malloc(globalx*sizeof(subStruct*)); for(int i=0;i<globalx;i++) bar[i]=(*subStruct)malloc(globaly*sizeof(subStruct)); }; int main(){ globalx=2; globaly=3; bigStruct foo; for(int i=0;i<globalx;i++) for(int j=0;j<globaly;j++){ foo.bar[i][j].info1=i+j; foo.bar[i][j].info2=i*j; foo.bar[i][j].valid=(i==j); } return 0; } Note: in the program code I'm editing globalx and globaly were const's in a specified namespace. Now I removed the "const" so they can act as parameters that are set exactly once. Summarized: How can I properly allocate memory for the substruct inside the struct? Thank you very much! Max

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  • Why do I get Code Analysis CA1062 on an out parameter in this code?

    - by brickner
    I have a very simple code (simplified from the original code - so I know it's not a very clever code) that when I compile in Visual Studio 2010 with Code Analysis gives me warning CA1062: Validate arguments of public methods. public class Foo { protected static void Bar(out int[] x) { x = new int[1]; for (int i = 0; i != 1; ++i) x[i] = 1; } } The warning I get: CA1062 : Microsoft.Design : In externally visible method 'Foo.Bar(out int[])', validate local variable '(*x)', which was reassigned from parameter 'x', before using it. I don't understand why do I get this warning and how can I resolve it without suppressing it? Can new return null? Is this a Visual Studio 2010 bug?

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  • x86 Assembly Question about outputting

    - by jdea
    My code looks like this _declspec(naked) void f(unsigned int input,unsigned int *output) { __asm{ push dword ptr[esp+4] call factorial pop ecx mov [output], eax //copy result ret } } __declspec(naked) unsigned int factorial(unsigned int n) { __asm{ push esi mov esi, dword ptr [esp+8] cmp esi, 1 jg RECURSE mov eax, 1 jmp END RECURSE: dec esi push esi call factorial pop esi inc esi mul esi END: pop esi ret } } Its a factorial function and I'm trying to output the answer after it recursively calculates the number that was passed in But what I get returned as an output is the same large number I keep getting Not sure about what is wrong with my output, by I also see this error CXX0030: Error: expression cannot be evaluated Thanks!

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  • trace this java method

    - by Bader
    public static int ABC(int x, int y) { if(y==0) return(0); else return(x + ABC(x,y-1)); } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(ABC(5,3)); }

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  • Iterating backward

    - by MBennett
    Suppose I have a vector<int> myvec and I want to loop through all of the elements in reverse. I can think of a few ways of doing this: for (vector<int>::iterator it = myvec.end() - 1; it >= myvec.begin(); --it) { // do stuff here } for (vector<int>::reverse_iterator rit = myvec.rbegin(); rit != myvec.rend(); ++rit) { // do stuff here } for (int i = myvec.size() - 1; i >= 0; --i) { // do stuff here } So my question is when should I use each? Is there a difference? I know that the first one is dangerous because if I pass in an empty vector, then myvec.end() - 1 is undefined, but are there any other hazards or inefficiencies with this?

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  • C# wrapper for array of three pointers

    - by fergs
    I'm currently working on a C# wrapper to work with Dallmeier Common API light. See previous posting: http://stackoverflow.com/questions/2430089/c-wrapper-and-callbacks I've got pretty much everything 'wrapped' but I'm stuck on wrapping a callback which contains an array of three pointers & an array integers: dlm_setYUVDataCllback int(int SessionHandle, void (*callback) (long IPlayerID, unsigned char** yuvData, int* pitch, int width, int height, int64_t ts, char* extData)) Function Set callback, to receive current YUV image. Arguments SessionHandle: handle to current session. Return PlayerID (see callback). Callback - IPlayerId: id to the Player object - yuvData: array of three pointers to Y, U and V part of image The YUV format used is YUV420 planar (not packed). char *y = yuvData[0]; char *u = yuvData[1]; char *v = yuvData[2]; - pitch: array of integers for pitches for Y, U and V part of image - width: intrinsic width of image. - height - ts : timestamp of current frame - extData: additional data to frame How do I go about wrapping this in c#? Any help is much appreciated.

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  • How to call Android contacts list?

    - by aZn137
    Hi, I'm making an Android app, and need to call the phone's contact list. I need to call the contacts list function, pick a contact, then return to my app with the contact's name. Here's the code I got on the internet, but it doesnt work. Please help: import android.app.ListActivity; import android.content.Intent; import android.database.Cursor; import android.os.Bundle; import android.provider.Contacts.People; import android.view.View; import android.widget.ListAdapter; import android.widget.ListView; import android.widget.SimpleCursorAdapter; import android.widget.TextView; public class Contacts extends ListActivity { private ListAdapter mAdapter; public TextView pbContact; public static String PBCONTACT; public static final int ACTIVITY_EDIT=1; private static final int ACTIVITY_CREATE=0; // Called when the activity is first created. @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); Cursor C = getContentResolver().query(People.CONTENT_URI, null, null, null, null); startManagingCursor(C); String[] columns = new String[] {People.NAME}; int[] names = new int[] {R.id.row_entry}; mAdapter = new SimpleCursorAdapter(this, R.layout.mycontacts, C, columns, names); setListAdapter(mAdapter); } // end onCreate() // Called when contact is pressed @Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); Cursor C = (Cursor) mAdapter.getItem(position); PBCONTACT = C.getString(C.getColumnIndex(People.NAME)); // RHS 05/06 //pbContact = (TextView) findViewById(R.id.myContact); //pbContact.setText(new StringBuilder().append("b")); Intent i = new Intent(this, NoteEdit.class); startActivityForResult(i, ACTIVITY_CREATE); } }

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  • How to get values after dictionary sorting by values with linq

    - by user301639
    hey, I've a dictionary, which i sorted by value with linq, how can i get those sorted value from the sorted result i get that's what i did so far Dictionary<char, int> lettersAcurr = new Dictionary<char, int>();//sort by int value var sortedDict = (from entry in lettersAcurr orderby entry.Value descending select entry); during the debug i can see that sortedDic has a KeyValuePar, but i cant accesses to it thanks for help

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  • Why no DatePicker.setDateChangedListener() method

    - by OceanBlue
    Since most widgets have a standard method of setting a listener, setOnXXXListener(), just wondering why there is no setDateChangedListener() method for DatePicker? I know init(int, int, int, OnDateChangedListener) can be used for the same purpose, but surely there must be some reason why Google decided not to use the standard method here. I went through the API docs and couldn't find the reason. Would one of the gurus here know the answer to this?

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  • What is difference between my atoi() calls?

    - by Lucas
    I have a big number stored in a string and try to extract a single digit. But what are the differences between those calls? #include <iostream> #include <string> int main(){ std::string bigNumber = "93485720394857230"; char tmp = bigNumber.at(5); int digit = atoi(&tmp); int digit2 = atoi(&bigNumber.at(5)) int digit3 = atoi(&bigNumber.at(12)); std::cout << "digit: " << digit << std::endl; std::cout << "digit2: " << digit2 << std::endl; std::cout << "digit3: " << digit3 << std::endl; } This will produce the following output. digit: 7 digit2: 2147483647 digit3: 57230 The first one is the desired result. The second one seems to me to be a random number, which I cannot find in the string. The third one is the end of the string, but not just a single digit as I expected, but up from the 12th index to the end of the string. Can somebody explain the different outputs to me? EDIT: Would this be an acceptable solution? char tmp[2] = {bigNumber.at(5), '\0'}; int digit = atoi(tmp); std::cout << "digit: " << digit << std::endl;

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  • How can I set the TextColor of a TextAppearanceSpan?

    - by michael
    Hi, I currently able to create a Medium size TextAppearanceSpan, But how can I set the text color to a specified RBG color (say #c71585)? new TextAppearanceSpan(context, android.R.style.TextAppearance_Medium); I see there is a constructor for public TextAppearanceSpan(Context context, int appearance, int colorList) { But what is the int for colorList? Is there any example for this? Thank you.

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  • Need help in displaying data insider marquee

    - by user59637
    Hi all, I want to display news inside the marquee markup in my banking application but its not happening.Please somebody help me what is the error in my code.Here is my code: <marquee bgcolor="silver" direction="left" id="marq1" runat="server" behavior="scroll" scrolldelay="80" style="height: 19px" width="565"> <% String se = Session["countnews"].ToString(); for (int i = 0; i < int.Parse("" +se); i++) { %> <strong><%Response.Write("&nbsp;&nbsp;" + Session["news"+i] + "&nbsp;&nbsp;"); %></strong> <% } %> </marquee> public class News { DataSet ds = new DataSet("Bank"); SqlConnection conn; String check; SqlDataAdapter sda; int i; public string News_Name; public int Count_News; public int newsticker() { conn = new SqlConnection(ConfigurationManager.ConnectionStrings["BankingTransaction"].ConnectionString.ToString()); check = "Select NewsTitle from News where NewsStatus = 'A'"; sda = new SqlDataAdapter(check, conn); sda.Fill(ds, "News"); if (ds.Tables[0].Rows.Count > 0) { for (i = 0; i < ds.Tables[0].Rows.Count; i++) { News_Name =i+ ds.Tables[0].Rows[i].ItemArray[0].ToString(); } Count_News = ds.Tables[0].Rows.Count; } else { News_Name =0+ "Welcome to WestSide Bank Online Web site!"; Count_News = 1; } return int.Parse(Count_News.ToString()); } protected void Page_Load(object sender, EventArgs e) { News obj = new News(); try { obj.newsticker(); Session["news"] = obj.News_Name.ToString(); Session["countnews"] = obj.Count_News.ToString(); } catch (SqlException ex) { Response.Write("Error in login" + ex.Message); Response.Redirect("Default.aspx"); } finally { obj = null; } }

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  • Handling "Big" Integers in C#

    - by priyanka.sarkar
    How do I handle big integers in C#? I have a function that will give me the product of divisors: private static int GetDivisorProduct(int N, int product) { for (int i = 1; i < N; i++) { if (N % i == 0) { Console.WriteLine(i.ToString()); product *= i; } } return product; } The calling function is GetDivisorProduct(N, 1) If the result is bigger than 4 digits , I should obtain only the last 4 digits. ( E.g. If I give an input of 957, the output is 7493 after trimming out only the last four values. The actual result is 876467493.). Other sample inputs: If I give 10000, the output is 0. The BigInteger class has been removed from the C# library! How can I get the last four digits?

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  • Recursion with an Array; can't get the right value to return

    - by Matt
    Recursive Solution: Not working! Explanation: An integer, time, is passed into the function. It's then used to provide an end to the FOR statement (counter<time). The IF section (time == 0) provides a base case where the recursion should terminate, returning 0. The ELSE section is where the recursive call occurs: total is a private variable defined in the header file, elsewhere. It's initialized to 0 in a constructor, elsewhere. The function calls itself, recursively, adding productsAndSales[time-1][0] to total, again, and again, until the base call. Then the total is returned, and printed out later. Well, that's what I hoped for anyway. What I imagined would happen is that I would add up all the values in this one column of the array and the value would get returned, and printed out. Instead if returns 0. If I set the IF section to "return 1", I noticed that it returns powers of 2, for whatever value time is. EG: Time = 3, it returns 2*2 + 1. If time = 5, it returns 2*2*2*2 + 1. I don't understand why it's not returning the value I'm expecting. int CompanySales::calcTotals( int time ) { cout << setw( 4 ); if ( time == 0 ) { return 0; } else { return total += calcTotals( productsAndSales[ time-1 ][ 0 ]); } } Iterative Solution: Working! Explanation: An integer, time, is passed into the function. It's then used to provide an end to the FOR statement (counter<time). The FOR statement cycles through an array, adding all of the values in one column together. The value is then returned (and elsewhere in the program, printed out). Works perfectly. int CompanySales::calcTotals( int time ) { int total = 0; cout << setw( 4 ); for ( int counter = 0; counter < time; counter++ ) { total += productsAndSales[counter][0]; } return total0; }

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  • Arithmetic operator confusion

    - by Dusk
    Why I'm getting two different values while using the arithmetic operators for the same value of variables. I've just altered little bit my second program, which is resulted in giving me the different output. Could anyone please tell me why? int number=113; int rot=0; rot=number%10; rot*=100+number/10; System.out.println(rot);//333 int number=113; int rot=0; rot=number%10; rot=rot*100+number/10; System.out.println(rot);//311

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