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• How to inherit methods from a parent class in C++

  - by Pat

  When inheriting classes in C++ I understand members are inherited. But how does one inherit the methods as well? For example, in the below code, I'd like the method "getValues" to be accessible not through just CPoly, but also by any class that inherits it. So one can call "getValues" on CRect directly. class CPoly { private: int width, height; public: void getValues (int* a, int* b) { *a=width; *b=height;} }; class CRect: public CPoly { public: int area () { return (width * height); } }; In other words, is there any way to inherit methods for simple generic methods like getters and setters?

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• java: useful example of a shutdown hook?

  - by Jason S

  I'm trying to make sure my Java application takes reasonable steps to be robust, and part of that involves shutting down gracefully. I am reading about shutdown hooks and I don't actually get how to make use of them in practice. Is there a practical example out there? Let's say I had a really simple application like this one below, which writes numbers to a file, 10 to a line, in batches of 100, and I want to make sure a given batch finishes if the program is interrupted. I get how to register a shutdown hook but I have no idea how to integrate that into my application. Any suggestions? package com.example.test.concurrency; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.PrintWriter; public class GracefulShutdownTest1 { final private int N; final private File f; public GracefulShutdownTest1(File f, int N) { this.f=f; this.N = N; } public void run() { PrintWriter pw = null; try { FileOutputStream fos = new FileOutputStream(this.f); pw = new PrintWriter(fos); for (int i = 0; i < N; ++i) writeBatch(pw, i); } catch (FileNotFoundException e) { e.printStackTrace(); } finally { pw.close(); } } private void writeBatch(PrintWriter pw, int i) { for (int j = 0; j < 100; ++j) { int k = i*100+j; pw.write(Integer.toString(k)); if ((j+1)%10 == 0) pw.write('\n'); else pw.write(' '); } } static public void main(String[] args) { if (args.length < 2) { System.out.println("args = [file] [N] " +"where file = output filename, N=batch count"); } else { new GracefulShutdownTest1( new File(args[0]), Integer.parseInt(args[1]) ).run(); } } }

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• Running for loop depending on size of string vector

  - by xbonez

  I have made a string vector vector actor_; and then added elements in it using push_back. I now want to display all of them, for which I need to run a loop according to the number of elements in the vector. For that, I need to run the following loop: for (int i = 0; i < (int)actor_.size; i++) { } but this returns the following error: error C2440: 'type cast' : cannot convert from 'unsigned int (__thiscall std::vector<_Ty::* )(void) const' to 'int' 1 with 1 [ 1 _Ty=std::string 1 ] 1 There is no context in which this conversion is possible

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• C programming, why does this large array declaration produce a segmentation fault?

  - by noneme

  This code produces a segmentation fault during the array declaration. I'm confused as to why this happens. I intentionally selected 2000000000 as a value because it is below 2^31 and can fit into an integer variable. int main() { int nums_size = 2000000000; int nums[nums_size]; int i; for(i = 0; i < nums_size; i++) { nums[i] = i; } return 0; }

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• Multiple declarations and definations

  - by Yogesh

  X.c >> ------------------------- int i; main () { fun (); } ------------------------- Y.c >> int i; fun () { } why does these two files compile with no error ? (using GCC) but if i use int i = 10; throws multiple definition error

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• how can this inner enum code be improved ?

  - by mafalda

  I have this construct public class Constants{ enum SystemA implements Marker{ ConstOne(1), ConstTwo(2), ConstThree(3); SystemA(int i) { number =i; } int number; } enum SystemB implements Marker{ ConstFour(4), ConstFive(5), ConstSix(6); SystemB(int i) { number =i; } int number; } } I have Marker so I can pass to method like this method(Constants.SystemA) or method(Constants.SystemB) What is the best way to list all the enum values ? I also want to make sure that it is not duplicating the number in any of the enums

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• Why this doesnt't work in C++?

  - by user3377450

  I'm doing something and I have this: //main.cpp file template<typename t1, typename t2> std::ostream& operator<<(std::ostream& os, const std::pair<t1, t2>& pair) { return os << "< " << pair.first << " , " << pair.second << " >"; } int main() { std::map<int, int> map = { { 1, 2 }, { 2, 3 } }; std::cout << *map.begin() << std::endl;//This works std::copy(map.begin(), map.end(), std::ostream_iterator<std::pair<int,int> >(std::cout, " "));//this doesn't work } I guess this is not working because in the std::copy algorithm the operator isn't defined, but what can I do?

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• byte and short data types in Java can accept the value outside the range by explicit cast. The higher data types however can not. Why?

  - by Lion

  Let's consider the following expressions in Java. byte a = 32; byte b = (byte) 250; int i = a + b; This is valid in Java even though the expression byte b = (byte) 250; is forced to assign the value 250 to b which is outside the range of the type byte. Therefore, b is assigned -6 and consequently i is assigned the value 26 through the statement int i = a + b;. The same thing is possible with short as follows. short s1=(short) 567889999; Although the specified value is outside the range of short, this statement is legal. The same thing is however wrong with higher data types such int, double, folat etc and hence, the following case is invalid and causes a compile-time error. int z=2147483648; This is illegal, since the range of int in Java is from -2,147,483,648 to 2147483647 which the above statement exceeds and issues a compile-time error. Why is such not wrong with byte and short data types in Java?

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• How do I make this Java code operate properly? [Multi-threaded, race condition]

  - by Fixee

  I got this code from a student, and it does not work properly because of a race condition involving x++ and x--. He added synchronized to the run() method trying to get rid of this bug, but obviously this only excludes threads from entering run() on the same object (which was never a problem in the first place) but doesn't prevent independent objects from updating the same static variable x at the same time. public class DataRace implements Runnable { static volatile int x; public synchronized void run() { for (int i = 0; i < 10000; i++) { x++; x--; } } public static void main(String[] args) throws Exception { Thread [] threads = new Thread[100]; for (int i = 0; i < threads.length; i++) threads[i] = new Thread(new DataRace()); for (int i = 0; i < threads.length; i++) threads[i].start(); for (int i = 0; i < threads.length; i++) threads[i].join(); System.out.println(x); // x not always 0! } } Since we cannot synchronize on x (because it is primitive), the best solution I can think of is to create a new static object like static String lock = ""; and enclose the x++ and x-- within a synchronized block, locking on lock. But this seems really awkward. Is there a better way?

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• ANSI C++: Diferences between delete and delete[]

  - by Sunscreen

  I was looking a snipset of code: int* ip; ip = new int[100]; delete ip; The example above states that: "This code will work with many compilers, but it should instead read:" int* ip; ip = new int[100]; delete [] ip; Is this indeed the case? I use the compiler "Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 11.00.7022 for 80x86" and does not complain (first example) while compiling. At runtime the pointer is set to NULL. Other compilers behave diferrently? Can a compiler not compain and issues can appear at runtime? Thanks, Sun

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• OnSize() Problem in VC++

  - by Anu

  Hi, In my VC++ MFC applcaiton,i have different views.And in each view,when i maximize it,i changed the size and position to new thing(Normally it fully get maximixed to screen size).But i dont want tht.So in OnSize() i coded like this. void CChildFrame::OnSize(UINT nType, int cx, int cy) { CMDIChildWnd::OnSize(nType, cx, cy); int XBorder = GetSystemMetrics(SM_CXMAXIMIZED); int YBorder = GetSystemMetrics(SM_CYMAXIMIZED); switch (nType) { case SIZE_MAXIMIZED: SetWindowPos(NULL,0,60,XBorder-45,YBorder-60,SWP_NOZORDER ); break; } } But what happened is?When i maximize the view,its get maximized to above mention size only.But in that blue bar,there si no minimize,maximize,close button. When i double click in the blue bar,its get to resumed to previous postion with all buttons. How can i get that?

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• Converting a string into a double

  - by Koning Baard

  I am trying to convert a string (const char* argv[]) to a double precision floating point number: int main(const int argc, const char *argv[]) { int i; double numbers[argc - 1]; for(i = 1; i < argc; i += 1) { /* -- Convert each argv into a double and put it in `number` */ } /* ... */ return 0; } Can anyone help me? Thanks

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• Detect if class has overloaded function fails on Comeau compiler

  - by Frank

  Hi Everyone, I'm trying to use SFINAE to detect if a class has an overloaded member function that takes a certain type. The code I have seems to work correctly in Visual Studio and GCC, but does not compile using the Comeau online compiler. Here is the code I'm using: #include <stdio.h> //Comeau doesnt' have boost, so define our own enable_if_c template<bool value> struct enable_if_c { typedef void type; }; template<> struct enable_if_c< false > {}; //Class that has the overloaded member function class TestClass { public: void Func(float value) { printf( "%f\n", value ); } void Func(int value) { printf( "%i\n", value ); } }; //Struct to detect if TestClass has an overloaded member function for type T template<typename T> struct HasFunc { template<typename U, void (TestClass::*)( U )> struct SFINAE {}; template<typename U> static char Test(SFINAE<U, &TestClass::Func>*); template<typename U> static int Test(...); static const bool Has = sizeof(Test<T>(0)) == sizeof(char); }; //Use enable_if_c to only allow the function call if TestClass has a valid overload for T template<typename T> typename enable_if_c<HasFunc<T>::Has>::type CallFunc(TestClass &test, T value) { test.Func( value ); } int main() { float value1 = 0.0f; int value2 = 0; TestClass testClass; CallFunc( testClass, value1 ); //Should call TestClass::Func( float ) CallFunc( testClass, value2 ); //Should call TestClass::Func( int ) } The error message is: no instance of function template "CallFunc" matches the argument list. It seems that HasFunc::Has is false for int and float when it should be true. Is this a bug in the Comeau compiler? Am I doing something that's not standard? And if so, what do I need to do to fix it?

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• C++ How fast is passing around objects?

  - by wndsr

  Assuming we are running a compiled C++ binary: Is passing around an int (e.g. function to function, or writing it into variables) slower than passing around structs/class objects like the following? class myClass { int a; int b; char c; vector d; string e; }

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• Help me understand this Strange C++ code

  - by java lava

  Hi! This was a question in our old C++ exam. This code is driving me crazy, could anyone explain what it does and - especially - why? int arr[3]={10,20,30}; int *arrp = new int; (*(arr+1)+=3)+=5; (arrp=&arr[0])++; std::cout<<*arrp;

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• What does this C++ construct do?

  - by cambr

  Somewhere in lines of code, I came across this construct... //void* v = void* value from an iterator int i = (int)(long(v)) What possible purpose can this contruct serve? Why not simply use int(v) instead? Why the cast to long first?

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• Efficient way to call .Sum() on multiple properties

  - by SherCoder

  I have a function that uses Linq to get data from the database and then I call that function in another function to sum all the individual properties using .Sum on each individual property. I was wondering if there is an efficient way to sum all the properties at once rather than calling .Sum() on each individual property. I think the way I am doing as of right now, is very slow (although untested). public OminitureStats GetAvgOmnitureData(int? fnsId, int dateRange) { IQueryable<OminitureStats> query = GetOmnitureDataAsQueryable(fnsId, dateRange); int pageViews = query.Sum(q => q.PageViews); int monthlyUniqueVisitors = query.Sum(q => q.MonthlyUniqueVisitors); int visits = query.Sum(q => q.Visits); double pagesPerVisit = (double)query.Sum(q => q.PagesPerVisit); double bounceRate = (double)query.Sum(q => q.BounceRate); return new OminitureStats(pageViews, monthlyUniqueVisitors, visits, bounceRate, pagesPerVisit); }

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• Do running times match with O(nlogn)?

  - by user472221

  Hi I have written a class(greedy strategy) that at first i used sort method which has O(nlogn) Collections.sort(array, new SortingObjectsWithProbabilityField()); and then i used the insert method of binary search tree which takes O(h) and h here is the tree height. for different n ,the running time will be : n,running time 17,515428 33,783340 65,540572 129,1285080 257,2052216 513,4299709 which I think is not correct because for increasing n , the running time should almost increase. This method will take the running time: Exponent = -1; for(int n = 2;n<1000;n+=Math.pow(2,exponent){ for (int j = 1; j <= 3; j++) { Random rand = new Random(); for (int i = 0; i < n; i++) { Element e = new Element(rand.nextInt(100) + 1, rand.nextInt(100) + 1, 0); for (int k = 0; k < i; k++) { if (e.getDigit() == randList.get(k).getDigit()) { e.setDigit(e.getDigit() + 1); } } randList.add(e); } double sum = 0.0; for (int i = 0; i < randList.size(); i++) { sum += randList.get(i).getProbability(); } for (Element i : randList) { i.setProbability(i.getProbability() / sum); } //Get time. long t2 = System.nanoTime(); GreedyVersion greedy = new GreedyVersion((ArrayList<Element>) randList); long t3 = System.nanoTime(); timeForGreedy = timeForGreedy + t3 - t2; } System.out.println(n + "," + "," + timeForGreedy/3 ); exponent++; } thanks

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• Processing a resultset to look up foriegn keys (and poulate a new table!)

  - by Gilly

  Hi, I've been handed a dataset that has some fairly basic table structures with no keys at all. eg {myRubishTable} - Area(varchar),AuthorityName(varchar),StartYear(varchar),StartMonth(varcha),EndYear(varchar),EndMonth(varchar),Amount(Money) there are other tables that use the Area and AuthorityName columns as well as a general use of Month and Years so I I figured a good first step was to pull Area and Authority into their own tables. I now want to process the data in the original table and lookup the key value to put into my new table with foreign keys which looks like this. (lookup Tables) {Area} - id (int, PK), name (varchar(50)) {AuthorityName} - id(int, PK), name(varchar(50) (TargetTable) {myBetterTable} - id (int,PK), area_id(int FK-Area),authority_name_id(int FK-AuthorityName),StartYear (varchar),StartMonth(varchar),EndYear(varchar),EndMonth(varchar),Amount(money) so row one in the old table read MYAREA, MYAUTHORITY,2009,Jan,2010,Feb,10000 and I want to populate the new table with 1,1,1,2009,Jan,2010,Feb,10000 where the first '1' is the primary key and the second two '1's are the ids in the lookup tables. Can anyone point me to the most efficient way of achieving this using just SQL? Thanks in advance Footnote:- I've achieved what I needed with some pretty simple WHERE clauses (I had left a rogue tablename in the FROM which was throwing me :o( ) but would be interested to know if this is the most efficient. ie SELECT [area].[area_id], [authority].[authority_name_id], [myRubishTable].[StartYear], [myRubishTable].[StartMonth], [myRubishTable].[EndYear], [myRubishTable].[EndMonth], [myRubishTable].[Amount] FROM [myRubishTable],[Area],[AuthorityName] WHERE [myRubishTable].[Area]=[Area].[name] AND [myRubishTable].[Authority Name]=[dim_AuthorityName].[name] TIA

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• Segmentation fault C++ in recursive function

  - by user69514

  Why do I get a segmentation fault in my recursive function. It happens every time i call it when a value greater than 4 as a parameter #include <iostream> #include <limits> using namespace std; int printSeries(int n){ if(n==1){ return 1; } else if( n==2){ return 2; } else if( n==3){ return 3; } else if( n==4){ return printSeries(1) + printSeries(2) + printSeries(3); } else{ return printSeries(n-3) + printSeries((n-2) + printSeries(n-1)); } } int main(){ //double infinity = numeric_limits<double>::max(); for(int i=1; i<=10; i++){ cout << printSeries(i) << endl; } return 0; }

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• Strange python error

  - by Werner

  Hi, I am trying to write a python program that calculates a histogram, given a list of numbers like: 1 3 2 3 4 5 3.2 4 2 2 so the input parameters are the filename and the number of intervals. The program code is: #!/usr/bin/env python import os, sys, re, string, array, math import numpy Lista = [] db = sys.argv[1] db_file = open(db,"r") ic=0 nintervals= int(sys.argv[2]) while 1: line = db_file.readline() if not line: break ll=string.split(line) #print ll[6] Lista.insert(ic,float(ll[0])) ic=ic+1 lmin=min(Lista) print "min= ",lmin lmax=max(Lista) print "max= ",lmax width=666.666 width=(lmax-lmin)/nintervals print "width= ",width nelements=len(Lista) print "nelements= ",nelements print " " Histogram = numpy.zeros(shape=(nintervals)) for item in Lista: #print item int_number = 1 + int((item-lmin)/width) print " " print "item,lmin= ",item,lmin print "(item-lmin)/width= ",(item-lmin)," / ",width," ====== ",(float(item)-float(lmin))/float(width) print "int((item-lmin)/width)= ",int((item-lmin)/width) print item , " belongs to interval ", int_number, " which is from ", lmin+width*(int_number-1), " to ",lmin+width*int_number Histogram[int_number] = Histogram[int_number] + 1 4 but somehow I am completely lost, I get strange errors, can anybody help¿ Thanks

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• How can i solve "0 " value try to get length value?

  - by Phsika

  if i try to add int value into array with string length Whole data is "0" why? and how can solve it? for (int j = 0; j < dTable.Columns.Count; j++) for (int i = 0; i < dTable.Rows.Count; i++) { mycounter[i] = dTable.Rows[i][j].ToString().Length; } it is not related to mycounter because: string test = ""; foreach(DataColumn dc in dTable.Columns) for (int i = 0; i < dTable.Rows.Count; i++) { // MessageBox.Show(dTable.Rows[i][dc].ToString()); test = dTable.Rows[i][dc].ToString().Length.ToString(); }

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• Java Error When correct code is put together

  - by Eric

  I have a few string problems that I need to put together for a complete homework assignment. They all work correctly by themselves, but when I put them together in the main function, the last one that finds the smallest word in a string gives an error. Anyone know why? public static void main(String[] args){ Scanner sc = new Scanner(System.in); //Length of Word String word1 = sc.next(); System.out.println(word1.length()); //Evens in one string odds in the other String word2 = sc.next(); StringBuilder even = new StringBuilder(); StringBuilder odd = new StringBuilder(); for(int i = 0; i < word2.length(); i++){ if(i % 2 == 0){ even.append(word2.charAt(i)); } else{ odd.append(word2.charAt(i)); } } System.out.println(even + " " + odd); //Diminishing Suffix String word3 = sc.next(); for(int j = 0; j < word3.length(); j++){ System.out.print(word3.substring(j, word3.length()) + " "); } System.out.printf("\n"); //Letter Replacement String word4 = sc.next(); String word5 = sc.next(); String word6 = sc.next(); String word7 = word4.replace(word5, word6); System.out.println(word7); //How many times x appears in xstring String word8 = sc.next(); String word9 = sc.next(); int index = word8.indexOf(word9); int count = 0; while (index != -1) { count++; word8 = word8.substring(index + 1); index = word8.indexOf(word9); } System.out.println(count); System.out.println(); //Lexicographically smallest word String Sentence = sc.nextLine(); String[] myWords = Sentence.split(" "); int shortestLengths, shortestLocation; shortestLengths=(myWords[1]).length(); shortestLocation=1; for (int i = 1; i <myWords.length; i++) { if ((myWords[i]).length() < shortestLengths) { shortestLengths=(myWords[i]).length(); shortestLocation=i; } } System.out.println(myWords[shortestLocation]); } } Talking about the lexicographically smallest one

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• C++ vector reference parameter

  - by Archanimus

  Hello folks, let's say we have a class class MyClass { vector<vector<int > > myMatrice; public : MyClass(vector<vector<int > > &); } MyClass::MyClass(vector<vector<int > > & m) { myMatrice = m; } During the instanciation of MyClass, I pass a big vector < vector < int and I find that the object is actually copied and not only the reference, so it takes the double of the memory ... Please, can anyone help me out with this problem, I'm stuck since too many time ... And thanks a lot!

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• Word Counter Implementation

  - by kenny

  Is there a better way than the following brute foce implementation of a c# word counting class? UPDATED CODE: Sorry! /// <summary> /// A word counting class. /// </summary> public class WordCounter { Dictionary<string, int> dictTest = new Dictionary<string, int> (); /// <summary> /// Enters a word and returns the current number of times that word was found. /// </summary> /// <param name="word">The word or string found.</param> /// <returns>Count of times Found() was called with provided word.</returns> public int Found ( string word ) { int count = 1; return dictTest.TryGetValue ( word, out count ) ? ++dictTest[word] : dictTest[word] = 1; } }

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