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• Implementing default constructors

  - by James

  Implement the default constructor, the constructors with one and two int parameters. The one-parameter constructor should initialize the first member of the pair, the second member of the pair is to be 0. Overload binary operator + to add the pairs as follows: (a, b) + (c, d) = (a + c, b + d); Overload the - analogously. Overload the * on pairs ant int as follows: (a, b) * c = (a * c, b * c). Write a program to test all the member functions and overloaded operators in your class definition. You will also need to write accessor (get) functions for each member. The definition of the class Pairs: class Pairs { public: Pairs(); Pairs(int first, int second); Pairs(int first); // other members and friends friend istream& operator>> (istream&, Pair&); friend ostream& operator<< (ostream&, const Pair&); private: int f; int s; }; Self-Test Exercise #17: istream& operator (istream& ins, Pair& second) { char ch; ins ch; // discard init '(' ins second.f; ins ch; // discard comma ',' ins second.s; ins ch; // discard final '(' return ins; } ostream& operator<< (ostream& outs, const Pair& second) { outs << '('; outs << second.f; outs << ", " ;// I followed the Author's suggestion here. outs << second.s; outs << ")"; return outs; }

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• Copy constructor bug

  - by user168715

  I'm writing a simple nD-vector class, but am encountering a strange bug. I've stripped out the class to the bare minimum that still reproduces the bug: #include <iostream> using namespace std; template<unsigned int size> class nvector { public: nvector() {data_ = new double[size];} ~nvector() {delete[] data_;} template<unsigned int size2> nvector(const nvector<size2> &other) { data_ = new double[size]; int i=0; for(; i<size && i < size2; i++) data_[i] = other[i]; for(; i<size; i++) data_[i] = 0; } double &operator[](int i) {return data_[i];} const double&operator[](int i) const {return data_[i];} private: const nvector<size> &operator=(const nvector<size> &other); //Intentionally unimplemented for now double *data_; }; int main() { nvector<2> vector2d; vector2d[0] = 1; vector2d[1] = 2; nvector<3> vector3d(vector2d); for(int i=0; i<3; i++) cout << vector3d[i] << " "; cout << endl; //Prints 1 2 0 nvector<3> other3d(vector3d); for(int i=0; i<3; i++) cout << other3d[i] << " "; cout << endl; //Prints 1 2 0 } //Segfault??? On the surface this seems to work fine, and both tests print out the correct values. However, at the end of main the program crashes with a segfault, which I've traced to nvector's destructor. At first I thought the (incorrect) default assignment operator was somehow being called, which is why I added the (currently) unimplemented explicit assignment operator to rule this possibility out. So my copy constructor must be buggy, but I'm having one of those days where I'm staring at extremely simple code and just can't see it. Do you guys have any ideas?

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• Can't insert a number into a C++ custom streambuf/ostream

  - by 0xbe5077ed

  I have written a custom std::basic_streambuf and std::basic_ostream because I want an output stream that I can get a JNI string from in a manner similar to how you can call std::ostringstream::str(). These classes are quite simple. namespace myns { class jni_utf16_streambuf : public std::basic_streambuf<char16_t> { JNIEnv * d_env; std::vector<char16_t> d_buf; virtual int_type overflow(int_type); public: jni_utf16_streambuf(JNIEnv *); jstring jstr() const; }; typedef std::basic_ostream<char16_t, std::char_traits<char16_t>> utf16_ostream; class jni_utf16_ostream : public utf16_ostream { jni_utf16_streambuf d_buf; public: jni_utf16_ostream(JNIEnv *); jstring jstr() const; }; // ... } // namespace myns In addition, I have made four overloads of operator<<, all in the same namespace: namespace myns { // ... utf16_ostream& operator<<(utf16_ostream&, jstring) throw(std::bad_cast); utf16_ostream& operator<<(utf16_ostream&, const char *); utf16_ostream& operator<<(utf16_ostream&, const jni_utf16_string_region&); jni_utf16_ostream& operator<<(jni_utf16_ostream&, jstring); // ... } // namespace myns The implementation of jni_utf16_streambuf::overflow(int_type) is trivial. It just doubles the buffer width, puts the requested character, and sets the base, put, and end pointers correctly. It is tested and I am quite sure it works. The jni_utf16_ostream works fine inserting unicode characters. For example, this works fine and results in the stream containing "hello, world": myns::jni_utf16_ostream o(env); o << u"hello, wor" << u'l' << u'd'; My problem is as soon as I try to insert an integer value, the stream's bad bit gets set, for example: myns::jni_utf16_ostream o(env); if (o.badbit()) throw "bad bit before"; // does not throw int32_t x(5); o << x; if (o.badbit()) throw "bad bit after"; // throws :( I don't understand why this is happening! Is there some other method on std::basic_streambuf I need to be implementing????

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• SQL SERVER – Merge Operations – Insert, Update, Delete in Single Execution

  - by pinaldave

  This blog post is written in response to T-SQL Tuesday hosted by Jorge Segarra (aka SQLChicken). I have been very active using these Merge operations in my development. However, I have found out from my consultancy work and friends that these amazing operations are not utilized by them most of the time. Here is my attempt to bring the necessity of using the Merge Operation to surface one more time. MERGE is a new feature that provides an efficient way to do multiple DML operations. In earlier versions of SQL Server, we had to write separate statements to INSERT, UPDATE, or DELETE data based on certain conditions; however, at present, by using the MERGE statement, we can include the logic of such data changes in one statement that even checks when the data is matched and then just update it, and similarly, when the data is unmatched, it is inserted. One of the most important advantages of MERGE statement is that the entire data are read and processed only once. In earlier versions, three different statements had to be written to process three different activities (INSERT, UPDATE or DELETE); however, by using MERGE statement, all the update activities can be done in one pass of database table. I have written about these Merge Operations earlier in my blog post over here SQL SERVER – 2008 – Introduction to Merge Statement – One Statement for INSERT, UPDATE, DELETE. I was asked by one of the readers that how do we know that this operator was doing everything in single pass and was not calling this Merge Operator multiple times. Let us run the same example which I have used earlier; I am listing the same here again for convenience. --Let’s create Student Details and StudentTotalMarks and inserted some records. USE tempdb GO CREATE TABLE StudentDetails ( StudentID INTEGER PRIMARY KEY, StudentName VARCHAR(15) ) GO INSERT INTO StudentDetails VALUES(1,'SMITH') INSERT INTO StudentDetails VALUES(2,'ALLEN') INSERT INTO StudentDetails VALUES(3,'JONES') INSERT INTO StudentDetails VALUES(4,'MARTIN') INSERT INTO StudentDetails VALUES(5,'JAMES') GO CREATE TABLE StudentTotalMarks ( StudentID INTEGER REFERENCES StudentDetails, StudentMarks INTEGER ) GO INSERT INTO StudentTotalMarks VALUES(1,230) INSERT INTO StudentTotalMarks VALUES(2,255) INSERT INTO StudentTotalMarks VALUES(3,200) GO -- Select from Table SELECT * FROM StudentDetails GO SELECT * FROM StudentTotalMarks GO -- Merge Statement MERGE StudentTotalMarks AS stm USING (SELECT StudentID,StudentName FROM StudentDetails) AS sd ON stm.StudentID = sd.StudentID WHEN MATCHED AND stm.StudentMarks > 250 THEN DELETE WHEN MATCHED THEN UPDATE SET stm.StudentMarks = stm.StudentMarks + 25 WHEN NOT MATCHED THEN INSERT(StudentID,StudentMarks) VALUES(sd.StudentID,25); GO -- Select from Table SELECT * FROM StudentDetails GO SELECT * FROM StudentTotalMarks GO -- Clean up DROP TABLE StudentDetails GO DROP TABLE StudentTotalMarks GO The Merge Join performs very well and the following result is obtained. Let us check the execution plan for the merge operator. You can click on following image to enlarge it. Let us evaluate the execution plan for the Table Merge Operator only. We can clearly see that the Number of Executions property suggests value 1. Which is quite clear that in a single PASS, the Merge Operation completes the operations of Insert, Update and Delete. I strongly suggest you all to use this operation, if possible, in your development. I have seen this operation implemented in many data warehousing applications. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, SQL, SQL Authority, SQL Joins, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Merge

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• concurrency::extent<N> from amp.h

  - by Daniel Moth

  Overview We saw in a previous post how index<N> represents a point in N-dimensional space and in this post we'll see how to define the N-dimensional space itself. With C++ AMP, an N-dimensional space can be specified with the template class extent<N> where you define the size of each dimension. From a look and feel perspective, you'd expect the programmatic interface of a point type and size type to be similar (even though the concepts are different). Indeed, exactly like index<N>, extent<N> is essentially a coordinate vector of N integers ordered from most- to least- significant, BUT each integer represents the size for that dimension (and hence cannot be negative). So, if you read the description of index, you won't be surprised with the below description of extent<N> There is the rank field returning the value of N you passed as the template parameter. You can construct one extent from another (via the copy constructor or the assignment operator), you can construct it by passing an integer array, or via convenience constructor overloads for 1- 2- and 3- dimension extents. Note that the parameterless constructor creates an extent of the specified rank with all bounds initialized to 0. You can access the components of the extent through the subscript operator (passing it an integer). You can perform some arithmetic operations between extent objects through operator overloading, i.e. ==, !=, +=, -=, +, -. There are operator overloads so that you can perform operations between an extent and an integer: -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, –= and, finally, there are additional overloads for plus and minus (+,-) between extent<N> and index<N> objects, returning a new extent object as the result. In addition to the usual suspects, extent offers a contains function that tests if an index is within the bounds of the extent (assuming an origin of zero). It also has a size function that returns the total linear size of this extent<N> in units of elements. Example code extent<2> e(3, 4); _ASSERT(e.rank == 2); _ASSERT(e.size() == 3 * 4); e += 3; e[1] += 6; e = e + index<2>(3,-4); _ASSERT(e == extent<2>(9, 9)); _ASSERT( e.contains(index<2>(8, 8))); _ASSERT(!e.contains(index<2>(8, 9))); grid<N> Our upcoming pre-release bits also have a similar type to extent, grid<N>. The way you create a grid is by passing it an extent, e.g. extent<3> e(4,2,6); grid<3> g(e); I am not going to dive deeper into grid, suffice for now to think of grid<N> simply as an alias for the extent<N> object, that you create when you encounter a function that expects a grid object instead of an extent object. Usage The extent class on its own simply defines the size of the N-dimensional space. We'll see in future posts that when you create containers (arrays) and wrappers (array_views) for your data, it is an extent<N> object that you'll need to use to create those (and use an index<N> object to index into them). We'll also see that it is a grid<N> object that you pass to the new parallel_for_each function that I'll cover in the next post. Comments about this post by Daniel Moth welcome at the original blog.

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• Not a statement?

  - by abelenky

  I have a simple little code fragment that is frustrating me: HashSet<long> groupUIDs = new HashSet<long>(); groupUIDs.Add(uid)? unique++ : dupes++; At compile time, it generates the error: Only assignment, call, increment, decrement, and new object expressions can be used as a statement HashSet.Add is documented to return a bool, so the ternary (?) operator should work, and this looks like a completely legitimate way to track the number of unique and duplicate items I add to a hash-set. When I reformat it as a if-then-else, it works fine. Can anyone explain the error, and if there is a way to do this as a simple ternary operator?

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• Exporting makefile from Eclipse CDT

  - by Alex Farber

  I have C++ project in the Ubuntu OS, Eclipse CDT. My final goal is to build the project binaries for FreeBSD OS. The first test. I create simple C++ CDT project with main.cpp file: cout << "OK" << endl; and build it. Then I open Terminal window in Release directory: alex@alex-linux:~/workspace/HelloWorld/Release$ ls HelloWorld main.d main.o makefile objects.mk sources.mk subdir.mk alex@alex-linux:~/workspace/HelloWorld/Release$ rm HelloWorld main.d main.o alex@alex-linux:~/workspace/HelloWorld/Release$ ls makefile objects.mk sources.mk subdir.mk alex@alex-linux:~/workspace/HelloWorld/Release$ make Building file: ../main.cpp Invoking: GCC C++ Compiler g++ -O3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp" Finished building: ../main.cpp Building target: HelloWorld Invoking: GCC C++ Linker g++ -o"HelloWorld" ./main.o Finished building target: HelloWorld alex@alex-linux:~/workspace/HelloWorld/Release$ ./HelloWorld OK alex@alex-linux:~/workspace/HelloWorld/Release$ So far, so good. Now I copy the whole project tree to FreeBSD and trying to build it: $ cd /home/alex/project $ ls main.cpp release $ cd release $ ls makefile objects.mk sources.mk subdir.mk $ make "makefile", line 5: Need an operator "makefile", line 10: Need an operator "makefile", line 11: Need an operator "makefile", line 12: Need an operator CDT-generated makefile doesn't work. This is makefile beginning: $ Automatically-generated file. Do not edit! -include ../makefile.init RM := rm -rf $ All of the sources participating in the build are defined here -include sources.mk -include subdir.mk -include objects.mk ... Line 5 is -include ../makefile.init. Really, there is no such file. But it works by some way on Ubuntu computer. What is the trick, how can I build this? BTW, manually written makefile works: all: g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp" g++ -o"HelloWorld" ./main.o Note: $ in makefile is actually #, I replaced it because # creates formatting problems inside of stackoverflow pre block.

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• Help with boost::lambda expression

  - by Venkat Shivanandan

  I tried to write a function that calculates a hamming distance between two codewords using the boost lambda library. I have the following code: #include <iostream> #include <numeric> #include <boost/function.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/if.hpp> #include <boost/bind.hpp> #include <boost/array.hpp> template<typename Container> int hammingDistance(Container & a, Container & b) { return std::inner_product( a.begin(), a.end(), b.begin(), (_1 + _2), boost::lambda::if_then_else_return(_1 != _2, 1, 0) ); } int main() { boost::array<int, 3> a = {1, 0, 1}, b = {0, 1, 1}; std::cout << hammingDistance(a, b) << std::endl; } And the error I am getting is: HammingDistance.cpp: In function ‘int hammingDistance(Container&, Container&)’: HammingDistance.cpp:15: error: no match for ‘operator+’ in ‘<unnamed>::_1 + <unnamed>::_2’ HammingDistance.cpp:17: error: no match for ‘operator!=’ in ‘<unnamed>::_1 != <unnamed>::_2’ /usr/include/c++/4.3/boost/function/function_base.hpp:757: note: candidates are: bool boost::operator!=(boost::detail::function::useless_clear_type*, const boost::function_base&) /usr/include/c++/4.3/boost/function/function_base.hpp:745: note: bool boost::operator!=(const boost::function_base&, boost::detail::function::useless_clear_type*) This is the first time I am playing with boost lambda. Please tell me where I am going wrong. Thanks.

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• "import numpy" tries to load my own package

  - by Sebastian

  I have a python (2.7) project containing my own packages util and operator (and so forth). I read about relative imports, but perhaps I didn't understand. I have the following directory structure: top-dir/ util/__init__.py (empty) util/ua.py util/ub.py operator/__init__.py ... test/test1.py The test1.py file contains #!/usr/bin/env python2 from __future__ import absolute_import # removing this line dosn't change anything. It's default functionality in python2.7 I guess import numpy as np It's fine when I execute test1.py inside the test/ folder. But when I move to the top-dir/ the import numpy wants to include my own util package: Traceback (most recent call last): File "tests/laplace_2d_square.py", line 4, in <module> import numpy as np File "/usr/lib/python2.7/site-packages/numpy/__init__.py", line 137, in <module> import add_newdocs File "/usr/lib/python2.7/site-packages/numpy/add_newdocs.py", line 9, in <module> from numpy.lib import add_newdoc File "/usr/lib/python2.7/site-packages/numpy/lib/__init__.py", line 4, in <module> from type_check import * File "/usr/lib/python2.7/site-packages/numpy/lib/type_check.py", line 8, in <module> import numpy.core.numeric as _nx File "/usr/lib/python2.7/site-packages/numpy/core/__init__.py", line 45, in <module> from numpy.testing import Tester File "/usr/lib/python2.7/site-packages/numpy/testing/__init__.py", line 8, in <module> from unittest import TestCase File "/usr/lib/python2.7/unittest/__init__.py", line 58, in <module> from .result import TestResult File "/usr/lib/python2.7/unittest/result.py", line 9, in <module> from . import util File "/usr/lib/python2.7/unittest/util.py", line 2, in <module> from collections import namedtuple, OrderedDict File "/usr/lib/python2.7/collections.py", line 9, in <module> from operator import itemgetter as _itemgetter, eq as _eq ImportError: cannot import name itemgetter The troublesome line is either from . import util or perhaps from operator import itemgetter as _itemgetter, eq as _eq What can I do?

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• 'SImple' 2 class Java calculator doesn't accept inputs or do calculations

  - by Tony O'Keeffe

  Hi, I'm trying to get a two class java calculator working (new to java) to work but so far i'm having no success. the two classes are outlined below, calcFrame is for the interface and calEngine should do the actual calculations but i can't get them to talk to one another. i'd really appreciate any assistance on same. Thanks. CalcFrame Code - import java.awt.; import javax.swing.; import javax.swing.border.; import java.awt.event.; /** *A Class that operates as the framework for a calculator. *No calculations are performed in this section */ public class CalcFrame implements ActionListener { private CalcEngine calc; private JFrame frame; private JTextField display; private JLabel status; /** * Constructor for objects of class GridLayoutExample */ public CalcFrame() { makeFrame(); //calc = engine; } /** * This allows you to quit the calculator. */ // Alows the class to quit. private void quit() { System.exit(0); } // Calls the dialog frame with the information about the project. private void showAbout() { JOptionPane.showMessageDialog(frame, "Group Project", "About Calculator Group Project", JOptionPane.INFORMATION_MESSAGE); } private void makeFrame() { frame = new JFrame("Group Project Calculator"); makeMenuBar(frame); JPanel contentPane = (JPanel)frame.getContentPane(); contentPane.setLayout(new BorderLayout(8, 8)); contentPane.setBorder(new EmptyBorder( 10, 10, 10, 10)); /** * Insert a text field */ display = new JTextField(); contentPane.add(display, BorderLayout.NORTH); //Container contentPane = frame.getContentPane(); contentPane.setLayout(new GridLayout(4, 4)); JPanel buttonPanel = new JPanel(new GridLayout(4, 4)); contentPane.add(new JButton("1")); contentPane.add(new JButton("2")); contentPane.add(new JButton("3")); contentPane.add(new JButton("4")); contentPane.add(new JButton("5")); contentPane.add(new JButton("6")); contentPane.add(new JButton("7")); contentPane.add(new JButton("8")); contentPane.add(new JButton("9")); contentPane.add(new JButton("0")); contentPane.add(new JButton("+")); contentPane.add(new JButton("-")); contentPane.add(new JButton("/")); contentPane.add(new JButton("*")); contentPane.add(new JButton("=")); contentPane.add(new JButton("C")); contentPane.add(buttonPanel, BorderLayout.CENTER); //status = new JLabel(calc.getAuthor()); //contentPane.add(status, BorderLayout.SOUTH); frame.pack(); frame.setVisible(true); } /** * Create the main frame's menu bar. * The frame that the menu bar should be added to. */ private void makeMenuBar(JFrame frame) { final int SHORTCUT_MASK = Toolkit.getDefaultToolkit().getMenuShortcutKeyMask(); JMenuBar menubar = new JMenuBar(); frame.setJMenuBar(menubar); JMenu menu; JMenuItem item; // create the File menu menu = new JMenu("File"); menubar.add(menu); // create the Quit menu with a shortcut "Q" key. item = new JMenuItem("Quit"); item.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, SHORTCUT_MASK)); item.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { quit(); } }); menu.add(item); // Adds an about menu. menu = new JMenu("About"); menubar.add(menu); // Displays item = new JMenuItem("Calculator Project"); item.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { showAbout(); } }); menu.add(item); } /** * An interface action has been performed. * Find out what it was and handle it. * @param event The event that has occured. */ public void actionPerformed(ActionEvent event) { String command = event.getActionCommand(); if(command.equals("0") || command.equals("1") || command.equals("2") || command.equals("3") || command.equals("4") || command.equals("5") || command.equals("6") || command.equals("7") || command.equals("8") || command.equals("9")) { int number = Integer.parseInt(command); calc.numberPressed(number); } else if(command.equals("+")) { calc.plus(); } else if(command.equals("-")) { calc.minus(); } else if(command.equals("=")) { calc.equals(); } else if(command.equals("C")) { calc.clear(); } else if(command.equals("?")) { } // else unknown command. redisplay(); } /** * Update the interface display to show the current value of the * calculator. */ private void redisplay() { display.setText("" + calc.getDisplayValue()); } /** * Toggle the info display in the calculator's status area between the * author and version information. */ } CalcEngine - public class CalcEngine { // The calculator's state is maintained in three fields: // buildingDisplayValue, haveLeftOperand, and lastOperator. // The current value (to be) shown in the display. private int displayValue; // The value of an existing left operand. private int leftOperand; /** * Create a CalcEngine. */ public CalcEngine() { clear(); } public int getDisplayValue() { return displayValue; } /** * A number button was pressed. * Either start a new operand, or incorporate this number as * the least significant digit of an existing one. * @param number The number pressed on the calculator. */ public void numberPressed(int number) { if(buildingDisplayValue) { // Incorporate this digit. displayValue = displayValue*10 + number; } else { // Start building a new number. displayValue = number; buildingDisplayValue = true; } } /** * The 'plus' button was pressed. */ public void plus() { applyOperator('+'); } /** * The 'minus' button was pressed. */ public void minus() { applyOperator('-'); } /** * The '=' button was pressed. */ public void equals() { // This should completes the building of a second operand, // so ensure that we really have a left operand, an operator // and a right operand. if(haveLeftOperand && lastOperator != '?' && buildingDisplayValue) { calculateResult(); lastOperator = '?'; buildingDisplayValue = false; } else { keySequenceError(); } } /** * The 'C' (clear) button was pressed. * Reset everything to a starting state. */ public void clear() { lastOperator = '?'; haveLeftOperand = false; buildingDisplayValue = false; displayValue = 0; } /** * @return The title of this calculation engine. */ public String getTitle() { return "Java Calculator"; } /** * @return The author of this engine. */ public String getAuthor() { return "David J. Barnes and Michael Kolling"; } /** * @return The version number of this engine. */ public String getVersion() { return "Version 1.0"; } /** * Combine leftOperand, lastOperator, and the * current display value. * The result becomes both the leftOperand and * the new display value. */ private void calculateResult() { switch(lastOperator) { case '+': displayValue = leftOperand + displayValue; haveLeftOperand = true; leftOperand = displayValue; break; case '-': displayValue = leftOperand - displayValue; haveLeftOperand = true; leftOperand = displayValue; break; default: keySequenceError(); break; } } /** * Apply an operator. * @param operator The operator to apply. */ private void applyOperator(char operator) { // If we are not in the process of building a new operand // then it is an error, unless we have just calculated a // result using '='. if(!buildingDisplayValue && !(haveLeftOperand && lastOperator == '?')) { keySequenceError(); return; } if(lastOperator != '?') { // First apply the previous operator. calculateResult(); } else { // The displayValue now becomes the left operand of this // new operator. haveLeftOperand = true; leftOperand = displayValue; } lastOperator = operator; buildingDisplayValue = false; } /** * Report an error in the sequence of keys that was pressed. */ private void keySequenceError() { System.out.println("A key sequence error has occurred."); // Reset everything. clear(); } }

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• Which non-clustered index should I use?

  - by Junior Mayhé

  Here I am studying nonclustered indexes on SQL Server Management Studio. I've created a table with more than 1 million records. This table has a primary key. CREATE TABLE [dbo].[Customers]( [CustomerId] [int] IDENTITY(1,1) NOT NULL, [CustomerName] [varchar](100) NOT NULL, [Deleted] [bit] NOT NULL, [Active] [bit] NOT NULL, CONSTRAINT [PK_Customers] PRIMARY KEY CLUSTERED ( [CustomerId] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] This is the query I'll be using to see what execution plan is showing: SELECT CustomerName FROM Customers Well, executing this command with no additional non-clustered index, it leads the execution plan to show me: I/O cost = 3.45646 Operator cost = 4.57715 Now I'm trying to see if it's possible to improve performance, so I've created a non-clustered index for this table: 1) First non-clustered index CREATE NONCLUSTERED INDEX [IX_CustomerID_CustomerName] ON [dbo].[Customers] ( [CustomerId] ASC, [CustomerName] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO Executing again the select against Customers table, the execution plan shows me: I/O cost = 2.79942 Operator cost = 3.92001 It seems better. Now I've deleted this just created non-clustered index, in order to create a new one: 2) First non-clustered index CREATE NONCLUSTERED INDEX [IX_CustomerIDIncludeCustomerName] ON [dbo].[Customers] ( [CustomerId] ASC ) INCLUDE ( [CustomerName]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this new non-clustered index, I've executed the select statement again and the execution plan shows me the same result: I/O cost = 2.79942 Operator cost = 3.92001 So, which non-clustered index should I use? Why the costs are the same on execution plan for I/O and Operator? Am I doing something wrong or this is expected? thank you

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• Disturbing or politically incorrect classes

  - by Jonas B

  Please don't take this seriously! - Community wikied Satire is always fun. Try to come up with the most shocking, disturbing or politically incorrect class you can think of. (But please no racism or anything seriously offensive or anything that can't be interpeted as satire). I'll go first with my example: public class Person { public bool Female; public Person(bool female) { Female = female; } public static bool operator <(Person j1, Person j2) { if (j1.Female && !j2.Female) return true; else return false; } public static bool operator >(Person j1, Person j2) { if (!j1.Female && j2.Female) return true; else return false; } public static bool operator <=(Person j1, Person j2) { if ((j1.Female == j2.Female) || (j1.Female && !j2.Female)) return true; else return false; } public static bool operator >=(Person j1, Person j2) { if ((j1.Female == j2.Female) || (!j1.Female && j2.Female)) return true; else return false; } }

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• Win32 DLL importing issues (DllMain)

  - by brady

  I have a native DLL that is a plug-in to a different application (one that I have essentially zero control of). Everything works just great until I link with an additional .lib file (links my DLL to another DLL named ABQSMABasCoreUtils.dll). This file contains some additional API from the parent application that I would like to utilize. I haven't even written any code to use any of the functions exported but just linking in this new DLL is causing problems. Specifically I get the following error when I attempt to run the program: The application failed to initialize properly (0xc0000025). Clock on OK to terminate the application. I believe I have read somewhere that this is typically due to a DllMain function returning FALSE. Also, the following message is written to the standard output: ERROR: Memory allocation attempted before component initialization I am almost 100% sure this error message is coming from the application and is not some type of Windows error. Looking into this a little more (aka flailing around and flipping every switch I know of) I linked with /MAP turned on and found this in the resulting .map file: 0001:000af220 ??3@YAXPEAX@Z 00000001800b0220 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll 0001:000af226 ??2@YAPEAX_K@Z 00000001800b0226 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll 0001:000af22c ??_U@YAPEAX_K@Z 00000001800b022c f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll 0001:000af232 ??_V@YAXPEAX@Z 00000001800b0232 f ABQSMABasCoreUtils_import:ABQSMABasCoreUtils.dll If I undecorate those names using "undname" they give the following (same order): void __cdecl operator delete(void * __ptr64) void * __ptr64 __cdecl operator new(unsigned __int64) void * __ptr64 __cdecl operator new[](unsigned __int64) void __cdecl operator delete[](void * __ptr64) I am not sure I understand how anything from ABQSMABasCoreUtils.dll can exist within this .map file or why my DLL is even attempting to load ABQSMABasCoreUtils.dll if I don't have any code that references this DLL. Can anyone help me put this information together and find out why this isn't working? For what it's worth I have confirmed via "dumpbin" that the parent application imports the same DLL (ABQSMABasCoreUtils.dll), so it is being loaded no matter what. I have also tried delay loading this DLL in my DLL but that did not change the results.

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• How do I improve my performance with this singly linked list struct within my program?

  - by Jesus

  Hey guys, I have a program that does operations of sets of strings. We have to implement functions such as addition and subtraction of two sets of strings. We are suppose to get it down to the point where performance if of O(N+M), where N,M are sets of strings. Right now, I believe my performance is at O(N*M), since I for each element of N, I go through every element of M. I'm particularly focused on getting the subtraction to the proper performance, as if I can get that down to proper performance, I believe I can carry that knowledge over to the rest of things I have to implement. The '-' operator is suppose to work like this, for example. Declare set1 to be an empty set. Declare set2 to be a set with { a b c } elements Declare set3 to be a set with ( b c d } elements set1 = set2 - set3 And now set1 is suppose to equal { a }. So basically, just remove any element from set3, that is also in set2. For the addition implementation (overloaded '+' operator), I also do the sorting of the strings (since we have to). All the functions work right now btw. So I was wondering if anyone could a) Confirm that currently I'm doing O(N*M) performance b) Give me some ideas/implementations on how to improve the performance to O(N+M) Note: I cannot add any member variables or functions to the class strSet or to the node structure. The implementation of the main program isn't very important, but I will post the code for my class definition and the implementation of the member functions: strSet2.h (Implementation of my class and struct) // Class to implement sets of strings // Implements operators for union, intersection, subtraction, // etc. for sets of strings // V1.1 15 Feb 2011 Added guard (#ifndef), deleted using namespace RCH #ifndef _STRSET_ #define _STRSET_ #include <iostream> #include <vector> #include <string> // Deleted: using namespace std; 15 Feb 2011 RCH struct node { std::string s1; node * next; }; class strSet { private: node * first; public: strSet (); // Create empty set strSet (std::string s); // Create singleton set strSet (const strSet &copy); // Copy constructor ~strSet (); // Destructor int SIZE() const; bool isMember (std::string s) const; strSet operator + (const strSet& rtSide); // Union strSet operator - (const strSet& rtSide); // Set subtraction strSet& operator = (const strSet& rtSide); // Assignment }; // End of strSet class #endif // _STRSET_ strSet2.cpp (implementation of member functions) #include <iostream> #include <vector> #include <string> #include "strset2.h" using namespace std; strSet::strSet() { first = NULL; } strSet::strSet(string s) { node *temp; temp = new node; temp->s1 = s; temp->next = NULL; first = temp; } strSet::strSet(const strSet& copy) { if(copy.first == NULL) { first = NULL; } else { node *n = copy.first; node *prev = NULL; while (n) { node *newNode = new node; newNode->s1 = n->s1; newNode->next = NULL; if (prev) { prev->next = newNode; } else { first = newNode; } prev = newNode; n = n->next; } } } strSet::~strSet() { if(first != NULL) { while(first->next != NULL) { node *nextNode = first->next; first->next = nextNode->next; delete nextNode; } } } int strSet::SIZE() const { int size = 0; node *temp = first; while(temp!=NULL) { size++; temp=temp->next; } return size; } bool strSet::isMember(string s) const { node *temp = first; while(temp != NULL) { if(temp->s1 == s) { return true; } temp = temp->next; } return false; } strSet strSet::operator + (const strSet& rtSide) { strSet newSet; newSet = *this; node *temp = rtSide.first; while(temp != NULL) { string newEle = temp->s1; if(!isMember(newEle)) { if(newSet.first==NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; newSet.first = newNode; } else if(newSet.SIZE() == 1) { if(newEle < newSet.first->s1) { node *tempNext = newSet.first; node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = tempNext; newSet.first = newNode; } else { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; newSet.first->next = newNode; } } else { node *prev = NULL; node *curr = newSet.first; while(curr != NULL) { if(newEle < curr->s1) { if(prev == NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = curr; newSet.first = newNode; break; } else { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = curr; prev->next = newNode; break; } } if(curr->next == NULL) { node *newNode; newNode = new node; newNode->s1 = newEle; newNode->next = NULL; curr->next = newNode; break; } prev = curr; curr = curr->next; } } } temp = temp->next; } return newSet; } strSet strSet::operator - (const strSet& rtSide) { strSet newSet; newSet = *this; node *temp = rtSide.first; while(temp != NULL) { string element = temp->s1; node *prev = NULL; node *curr = newSet.first; while(curr != NULL) { if( element < curr->s1 ) break; if( curr->s1 == element ) { if( prev == NULL) { node *duplicate = curr; newSet.first = newSet.first->next; delete duplicate; break; } else { node *duplicate = curr; prev->next = curr->next; delete duplicate; break; } } prev = curr; curr = curr->next; } temp = temp->next; } return newSet; } strSet& strSet::operator = (const strSet& rtSide) { if(this != &rtSide) { if(first != NULL) { while(first->next != NULL) { node *nextNode = first->next; first->next = nextNode->next; delete nextNode; } } if(rtSide.first == NULL) { first = NULL; } else { node *n = rtSide.first; node *prev = NULL; while (n) { node *newNode = new node; newNode->s1 = n->s1; newNode->next = NULL; if (prev) { prev->next = newNode; } else { first = newNode; } prev = newNode; n = n->next; } } } return *this; }

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• operators computing direction

  - by amiad

  Hi all! I enqunterd something that I can't understand. I have this code: cout << "f1 * f1 + f2 * f1 - f1 / f2 is: "<< f1 * f1 + f2 * f1 - f1 / f2 << endl; All the "f"s are objects, and all the operators are overloaded. The weird this is that the first computarion is of the "/" operator, then the second "" and then the first "", after that - the operator "+" and at last - operator "-". So basicly - the "/" and "*" worked from right to left, and the "+" and "-" operators worked from left to right. I made another test... I checked this code: cout << "f1 * f1 / f2 is: " << f1 * f1 / f2 << endl; Now, the first operator was "*" and only then oerator "/". So now, it worked from left to right. Can someone help me underatand why is there diffrence in the directions? 10X!

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• c++ queue template

  - by Dalton Conley

  ALright, pardon my messy code please. Below is my queue class. #include <iostream> using namespace std; #ifndef QUEUE #define QUEUE /*---------------------------------------------------------------------------- Student Class # Methods # Student() // default constructor Student(string, int) // constructor display() // out puts a student # Data Members # Name // string name Id // int id ----------------------------------------------------------------------------*/ class Student { public: Student() { } Student(string iname, int iid) { name = iname; id = iid; } void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } private: string name; int id; }; // define a typedef of a pointer to a student. typedef Student * StudentPointer; template <typename T> class Queue { public: /*------------------------------------------------------------------------ Queue Default Constructor Preconditions: none Postconditions: assigns default values for front and back to 0 description: constructs a default empty Queue. ------------------------------------------------------------------------*/ Queue() : myFront(0), myBack(0) {} /*------------------------------------------------------------------------ Copy Constructor Preconditions: requres a reference to a value for which you are copying Postconditions: assigns a copy to the parent Queue. description: Copys a queue and assigns it to the parent Queue. ------------------------------------------------------------------------*/ Queue(const T & q) { myFront = myBack = 0; if(!q.empty()) { // copy the first node myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } /*------------------------------------------------------------------------ Destructor Preconditions: none Postconditions: deallocates the dynamic memory for the Queue description: deletes the memory stored for a Queue. ------------------------------------------------------------------------*/ ~Queue() { NodePointer prev = myFront, ptr; while(prev != NULL) { ptr = prev->next; delete prev; prev = ptr; } } /*------------------------------------------------------------------------ Empty() Preconditions: none Postconditions: returns a boolean value. description: returns true/false based on if the queue is empty or full. ------------------------------------------------------------------------*/ bool empty() const { return (myFront == NULL); } /*------------------------------------------------------------------------ Enqueue Preconditions: requires a constant reference Postconditions: allocates memory and appends a value at the end of a queue description: ------------------------------------------------------------------------*/ void enqueue(const T & value) { NodePointer newNodePtr = new Node(value); if(empty()) { myFront = myBack = newNodePtr; newNodePtr->next = NULL; } else { myBack->next = newNodePtr; myBack = newNodePtr; newNodePtr->next = NULL; } } /*------------------------------------------------------------------------ Display Preconditions: requires a reference of type ostream Postconditions: returns the ostream value (for chaining) description: outputs the contents of a queue. ------------------------------------------------------------------------*/ void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } /*------------------------------------------------------------------------ Front Preconditions: none Postconditions: returns a value of type T description: returns the first value in the parent Queue. ------------------------------------------------------------------------*/ T front() const { if ( !empty() ) return (myFront->data); else { cerr << "*** Queue is empty -- returning garbage value ***\n"; T * temp = new(T); T garbage = * temp; delete temp; return garbage; } } /*------------------------------------------------------------------------ Dequeue Preconditions: none Postconditions: removes the first value in a queue ------------------------------------------------------------------------*/ void dequeue() { if ( !empty() ) { NodePointer ptr = myFront; myFront = myFront->next; delete ptr; if(myFront == NULL) myBack = NULL; } else { cerr << "*** Queue is empty -- " "can't remove a value ***\n"; exit(1); } } /*------------------------------------------------------------------------ pverloaded = operator Preconditions: requires a constant reference Postconditions: returns a const type T description: this allows assigning of queues to queues ------------------------------------------------------------------------*/ Queue<T> & operator=(const T &q) { // make sure we arent reassigning ourself // e.g. thisQueue = thisQueue. if(this != &q) { this->~Queue(); if(q.empty()) { myFront = myBack = NULL; } else { myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } return *this; } private: class Node { public: T data; Node * next; Node(T value, Node * first = 0) : data(value), next(first) {} }; typedef Node * NodePointer; NodePointer myFront, myBack, queueSize; }; /*------------------------------------------------------------------------ join Preconditions: requires 2 queue values Postconditions: appends queue2 to the end of queue1 description: this function joins 2 queues into 1. ------------------------------------------------------------------------*/ template <typename T> Queue<T> join(Queue<T> q1, Queue<T> q2) { Queue<T> q1Copy(q1), q2Copy(q2); Queue<T> jQueue; while(!q1Copy.empty()) { jQueue.enqueue(q1Copy.front()); q1Copy.dequeue(); } while(!q2Copy.empty()) { jQueue.enqueue(q2Copy.front()); q2Copy.dequeue(); } cout << jQueue << endl; return jQueue; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a Queue of type T Postconditions: returns the ostream (for chaining) description: this function is overloaded for outputing a queue with << ----------------------------------------------------------------------------*/ template <typename T> ostream & operator<<(ostream &out, Queue<T> &s) { s.display(out); return out; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of type Student Postconditions: none description: this function is overloaded for outputing an object of type Student. ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, Student &s) { s.display(out); } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of a pointer to a Student object. Postconditions: none description: this function is overloaded for outputing pointers to Students ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, StudentPointer &s) { s->display(out); } #endif Now I'm having some issues with it. For one, when I add 0 to a queue and then I output the queue like so.. Queue<double> qdub; qdub.enqueue(0); cout << qdub << endl; That works, it will output 0. But for example, if I modify that queue in any way.. like.. assign it to a different queue.. Queue<double> qdub1; Queue<double> qdub2; qdub1.enqueue(0; qdub2 = qdub1; cout << qdub2 << endl; It will give me weird values for 0 like.. 7.86914e-316. Help on this would be much appreciated!

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• Division by zero: Undefined Behavior or Implementation Defined in C and/or C++ ?

  - by SiegeX

  Regarding division by zero, the standards say: C99 6.5.5p5 - The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined. C++03 5.6.4 - The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second. If the second operand of / or % is zero the behavior is undefined. If we were to take the above paragraphs at face value, the answer is clearly Undefined Behavior for both languages. However, if we look further down in the C99 standard we see the following paragraph which appears to be contradictory(1): C99 7.12p4 - The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; Do the standards have some sort of golden rule where Undefined Behavior cannot be superseded by a (potentially) contradictory statement? Barring that, I don't think it's unreasonable to conclude that if your implementation defines the INFINITY macro, division by zero is defined to be such. However, if your implementation does not define such a macro, the behavior is Undefined. I'm curious what the consensus on this matter for each of the two languages. Would the answer change if we are talking about integer division int i = 1 / 0 versus floating point division float i = 1.0 / 0.0 ? Note (1) The C++03 standard talks about the library which includes the INFINITY macro.

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• multiple definition in header file

  - by Jérôme

  Here is a small code-example from which I'd like to ask a question : complex.h : #ifndef COMPLEX_H #define COMPLEX_H #include <iostream> class Complex { public: Complex(float Real, float Imaginary); float real() const { return m_Real; }; private: friend std::ostream& operator<<(std::ostream& o, const Complex& Cplx); float m_Real; float m_Imaginary; }; std::ostream& operator<<(std::ostream& o, const Complex& Cplx) { return o << Cplx.m_Real << " i" << Cplx.m_Imaginary; } #endif // COMPLEX_H complex.cpp : #include "complex.h" Complex::Complex(float Real, float Imaginary) { m_Real = Real; m_Imaginary = Imaginary; } main.cpp : #include "complex.h" #include <iostream> int main() { Complex Foo(3.4, 4.5); std::cout << Foo << "\n"; return 0; } When compiling this code, I get the following error : multiple definition of operator<<(std::ostream&, Complex const&) I've found that making this fonction inline solves the problem, but I don't understand why. Why does the compiler complain about multiple definition ? My header file is guarded (with #define COMPLEX_H). And, if complaining about the operator<< fonction, why not complain about the public real() fonction, which is defined in the header as well ? And is there another solution as using the inline keyword ?

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• The correct usage of nested #pragma omp for directives

  - by GoldenLee

  The following code runs like a charm before OpenMP parallelization was applied. In fact, the following code was in a state of endless loop! I'm sure that's result from my incorrect use to the OpenMP directives. Would you please show me the correct way? Thank you very much. #pragma omp parallel for for (int nY = nYTop; nY <= nYBottom; nY++) { for (int nX = nXLeft; nX <= nXRight; nX++) { // Use look-up table for performance dLon = theApp.m_LonLatLUT.LonGrid()[nY][nX] + m_FavoriteSVISSRParams.m_dNadirLon; dLat = theApp.m_LonLatLUT.LatGrid()[nY][nX]; // If you don't want to use longitude/latitude look-up table, uncomment the following line //NOMGeoLocate.XYToGEO(dLon, dLat, nX, nY); if (dLon > 180 || dLat > 180) { continue; } if (Navigation.GeoToXY(dX, dY, dLon, dLat, 0) > 0) { continue; } // Skip void data scanline dY = dY - nScanlineOffset; // Compute coefficients as well as its four neighboring points' values nX1 = int(dX); nX2 = nX1 + 1; nY1 = int(dY); nY2 = nY1 + 1; dCx = dX - nX1; dCy = dY - nY1; dP1 = pIRChannelData->operator [](nY1)[nX1]; dP2 = pIRChannelData->operator [](nY1)[nX2]; dP3 = pIRChannelData->operator [](nY2)[nX1]; dP4 = pIRChannelData->operator [](nY2)[nX2]; // Bilinear interpolation usNomDataBlock[nY][nX] = (unsigned short)BilinearInterpolation(dCx, dCy, dP1, dP2, dP3, dP4); } }

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• Getting a type for a template instantiation?

  - by ebo

  I have the following situation: I have a object of type MyClass, which has a method to cast itself to it's base class. The class includes a typedef for it's base class and a method to do the downcast. template <class T, class B> class BaseClass; template <class T> class NoAccess; template <class T> class MyClass : public BaseClass<T, NoAccess<T> > { private: typedef BaseClass<T, NoAccess<T> > base; public: base &to_base(); }; I need to pass the result of a base call to a functor Operator: template <class Y> class Operator { Operator(Y &x); }; Operator<???> op(myobject.to_base()); Is there a easy way to fill the ??? provided that I do not want to use NoAccess?

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• Syntax for finding structs in multisets - C++

  - by Sarah

  I can't seem to figure out the syntax for finding structs in containers. I have a multiset of Event structs. I'm trying to find one of these structs by searching on its key. I get the compiler error commented below. struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } bool operator > ( const Event & rhs ) const { return ( time > rhs.time ); } bool operator == ( const Event & rhs ) const { return ( time == rhs.time ); } double time; int eventID; int hostID; int s; }; typedef std::multiset< Event, std::less< Event > > EventPQ; EventPQ currentEvents; double oldRecTime = 20.0; EventPQ::iterator ceItr = currentEvents.find( EventPQ::key_type( oldRecTime ) ); // no matching function call I've tried a few permutations to no avail. I thought defining the conditional equality operator was going to be enough.

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• C++ Problem: Class Promotion using derived class

  - by Michael Fitzpatrick

  I have a class for Float32 that is derived from Float32_base class Float32_base { public: // Constructors Float32_base(float x) : value(x) {}; Float32_base(void) : value(0) {}; operator float32(void) {return value;}; Float32_base operator =(float x) {value = x; return *this;}; Float32_base operator +(float x) const { return value + x;}; protected: float value; } class Float32 : public Float32_base { public: float Tad() { return value + .01; } } int main() { Float32 x, y, z; x = 1; y = 2; // WILL NOT COMPILE! z = (x + y).Tad(); // COMPILES OK z = ((Float32)(x + y)).Tad(); } The issue is that the + operator returns a Float32_base and Tad() is not in that class. But 'x' and 'y' are Float32's. Is there a way that I can get the code in the first line to compile without having to resort to a typecast like I did on the next line?

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• Can't figure out where race condition is occuring

  - by Nik

  I'm using Valgrind --tool=drd to check my application that uses Boost::thread. Basically, the application populates a set of "Book" values with "Kehai" values based on inputs through a socket connection. On a seperate thread, a user can connect and get the books send to them. Its fairly simple, so i figured using a boost::mutex::scoped_lock on the location that serializes the book and the location that clears out the book data should be suffice to prevent any race conditions. Here is the code: void Book::clear() { boost::mutex::scoped_lock lock(dataMutex); for(int i =NUM_KEHAI-1; i >= 0; --i) { bid[i].clear(); ask[i].clear(); } } int Book::copyChangedKehaiToString(char* dst) const { boost::mutex::scoped_lock lock(dataMutex); sprintf(dst, "%-4s%-13s",market.c_str(),meigara.c_str()); int loc = 17; for(int i = 0; i < Book::NUM_KEHAI; ++i) { if(ask[i].changed > 0) { sprintf(dst+loc,"A%i%-21s%-21s%-21s%-8s%-4s",i,ask[i].price.c_str(),ask[i].volume.c_str(),ask[i].number.c_str(),ask[i].postTime.c_str(),ask[i].status.c_str()); loc += 77; } } for(int i = 0; i < Book::NUM_KEHAI; ++i) { if(bid[i].changed > 0) { sprintf(dst+loc,"B%i%-21s%-21s%-21s%-8s%-4s",i,bid[i].price.c_str(),bid[i].volume.c_str(),bid[i].number.c_str(),bid[i].postTime.c_str(),bid[i].status.c_str()); loc += 77; } } return loc; } The clear() function and the copyChangedKehaiToString() function are called in the datagetting thread and data sending thread,respectively. Also, as a note, the class Book: struct Book { private: Book(const Book&); Book& operator=(const Book&); public: static const int NUM_KEHAI=10; struct Kehai; friend struct Book::Kehai; struct Kehai { private: Kehai& operator=(const Kehai&); public: std::string price; std::string volume; std::string number; std::string postTime; std::string status; int changed; Kehai(); void copyFrom(const Kehai& other); Kehai(const Kehai& other); inline void clear() { price.assign(""); volume.assign(""); number.assign(""); postTime.assign(""); status.assign(""); changed = -1; } }; std::vector<Kehai> bid; std::vector<Kehai> ask; tm recTime; mutable boost::mutex dataMutex; Book(); void clear(); int copyChangedKehaiToString(char * dst) const; }; When using valgrind --tool=drd, i get race condition errors such as the one below: ==26330== Conflicting store by thread 1 at 0x0658fbb0 size 4 ==26330== at 0x653AE68: std::string::_M_mutate(unsigned int, unsigned int, unsigned int) (in /usr/lib/libstdc++.so.6.0.8) ==26330== by 0x653AFC9: std::string::_M_replace_safe(unsigned int, unsigned int, char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8) ==26330== by 0x653B064: std::string::assign(char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8) ==26330== by 0x653B134: std::string::assign(char const*) (in /usr/lib/libstdc++.so.6.0.8) ==26330== by 0x8055D64: Book::Kehai::clear() (Book.h:50) ==26330== by 0x8094A29: Book::clear() (Book.cpp:78) ==26330== by 0x808537E: RealKernel::start() (RealKernel.cpp:86) ==26330== by 0x804D15A: main (main.cpp:164) ==26330== Allocation context: BSS section of /usr/lib/libstdc++.so.6.0.8 ==26330== Other segment start (thread 2) ==26330== at 0x400BB59: pthread_mutex_unlock (drd_pthread_intercepts.c:633) ==26330== by 0xC59565: pthread_mutex_unlock (in /lib/libc-2.5.so) ==26330== by 0x805477C: boost::mutex::unlock() (mutex.hpp:56) ==26330== by 0x80547C9: boost::unique_lock<boost::mutex>::~unique_lock() (locks.hpp:340) ==26330== by 0x80949BA: Book::copyChangedKehaiToString(char*) const (Book.cpp:134) ==26330== by 0x80937EE: BookSerializer::serializeBook(Book const&, std::string const&) (BookSerializer.cpp:41) ==26330== by 0x8092D05: BookSnapshotManager::getSnaphotDataList() (BookSnapshotManager.cpp:72) ==26330== by 0x8088179: SnapshotServer::getDataList() (SnapshotServer.cpp:246) ==26330== by 0x808870F: SnapshotServer::run() (SnapshotServer.cpp:183) ==26330== by 0x808BAF5: boost::_mfi::mf0<void, RealThread>::operator()(RealThread*) const (mem_fn_template.hpp:49) ==26330== by 0x808BB4D: void boost::_bi::list1<boost::_bi::value<RealThread*> >::operator()<boost::_mfi::mf0<void, RealThread>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, RealThread>&, boost::_bi::list0&, int) (bind.hpp:253) ==26330== by 0x808BB90: boost::_bi::bind_t<void, boost::_mfi::mf0<void, RealThread>, boost::_bi::list1<boost::_bi::value<RealThread*> > >::operator()() (bind_template.hpp:20) ==26330== Other segment end (thread 2) ==26330== at 0x400B62A: pthread_mutex_lock (drd_pthread_intercepts.c:580) ==26330== by 0xC59535: pthread_mutex_lock (in /lib/libc-2.5.so) ==26330== by 0x80546B8: boost::mutex::lock() (mutex.hpp:51) ==26330== by 0x805473B: boost::unique_lock<boost::mutex>::lock() (locks.hpp:349) ==26330== by 0x8054769: boost::unique_lock<boost::mutex>::unique_lock(boost::mutex&) (locks.hpp:227) ==26330== by 0x8094711: Book::copyChangedKehaiToString(char*) const (Book.cpp:113) ==26330== by 0x80937EE: BookSerializer::serializeBook(Book const&, std::string const&) (BookSerializer.cpp:41) ==26330== by 0x808870F: SnapshotServer::run() (SnapshotServer.cpp:183) ==26330== by 0x808BAF5: boost::_mfi::mf0<void, RealThread>::operator()(RealThread*) const (mem_fn_template.hpp:49) ==26330== by 0x808BB4D: void boost::_bi::list1<boost::_bi::value<RealThread*> >::operator()<boost::_mfi::mf0<void, RealThread>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, RealThread>&, boost::_bi::list0&, int) (bind.hpp:253) For the life of me, i can't figure out where the race condition is. As far as I can tell, clearing the kehai is done only after having taken the mutex, and the same holds true with copying it to a string. Does anyone have any ideas what could be causing this, or where I should look? Thank you kindly.

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