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• Why _PROTOTYPE is used header files.

  - by mohit

  Why do we use _PROTOTYPE e.g. _PROTOTYPE( void *memset, (void *_s, int _c, size_t _n) I saw it in MINIX3 source code

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• how to use ByteArrayOutputStream and DataOutputStream simultaneously (Java)

  - by Manuel

  Hi! I'm having quite a problem here, and I think it is because I don't understand very much how I should use the API provided by Java. I need to write an int and a byte[] into a byte[] I thought of using a DataOutputStream to solve the data writing with writeInt(int i) and write(byte[] b), and to be able to put that into a byte array, I should use ByteArrayOutputStream's method toByteArray(). I understand that this classes use the Wrapper pattern, so I had two options: DataOutputStream w = new DataOutputStream(new ByteArrayOutputStream()); or ByteArrayOutputStream w = new ByteArrayOutputStream(new DataOutputStream()); but in both cases, I "loose" a method. in the first case, I can't access the toByteArray method, and in the second, I can't access the writeInt method. How should I use this classes together?

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• Getting input in system() function (Mac)

  - by Alex

  #include <iostream> using namespace std; int main() { short int enterVal; cout << "enter a number to say: " << endl; cin >> enterVal; system("say "%d"") << enterVal; return 0; } Is what I am currently trying. I want the user to enter a number and the system() function says it basically. The code above has an error which says " 'd' was not declared in this scope ". Thanks in advance.

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• Minimizing distance to a weighted grid

  - by Andrew Tomazos - Fathomling

  Lets suppose you have a 1000x1000 grid of positive integer weights W. We want to find the cell that minimizes the average weighted distance.to each cell. The brute force way to do this would be to loop over each candidate cell and calculate the distance: int best_x, best_y, best_dist; for x0 = 1:1000, for y0 = 1:1000, int total_dist = 0; for x1 = 1:1000, for y1 = 1:1000, total_dist += W[x1,y1] * sqrt((x0-x1)^2 + (y0-y1)^2); if (total_dist < best_dist) best_x = x0; best_y = y0; best_dist = total_dist; This takes ~10^12 operations, which is too long. Is there a way to do this in or near ~10^8 or so operations?

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• C++ Function Calling Itself

  - by Ben

  Suppose I wish to have a function that fills an array either in pattern x,y,x,y,x,ywhere x and y are variables defined by some algorithm and x,y,z,x,y,z where x, y and z are variables defined by the same algorithm. This should continue for all number of variables. Is this a viable way to implement it. int recurse_n(int n) { while(n > 0) { --n; recurse_n(n); n = 0; // Use algorithm here } }

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• Key that yields multiple Results

  - by SgtStud

  I'm pretty new to programming so I'm sorry if this is a stupid question. I was wondering if there was a type of data that returns (possibly) more than one answer per key. For example: TestType<int,String> test = new TestType<int,String>(); So if you typed, test.getKey(1), you could get {"hello","this","is","a","test"}. Basically, is there a type of data that can return multiple answers, sort of like a HashMap and List combined?

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• error message fix

  - by user1722654

  for (int i = 0; i < dataGridView1.Rows.Count; i++) { //bool sleected = false; if (dataGridView1.Rows[i].Cells[3].Value != null) { selected.Add(i); } } //string donew = ""; // line off error textBox1.Text = ((String)dataGridView1.Rows[1].Cells[2].Value); /* for (int i = 0; i < selected.Count; i++) { textAdded.Add((String)dataGridView1.Rows[0].Cells[2].Value); // donew += (String)dataGridView1.Rows[selected[i]].Cells[2].Value; }*/ I keep getting the error Unable to cast object of type 'System.Double' to type 'System.String' What can I do to overcome this?

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• Java: Best approach to have a long list of variables needed all the time without consuming memory?

  - by evilReiko

  I wrote an abstract class to contain all rules of the application because I need them almost everywhere in my application. So most of what it contains is static final variables, something like this: public abstract class appRules { public static final boolean IS_DEV = true; public static final String CLOCK_SHORT_TIME_FORMAT = "something"; public static final String CLOCK_SHORT_DATE_FORMAT = "something else"; public static final String CLOCK_FULL_FORMAT = "other thing"; public static final int USERNAME_MIN = 5; public static final int USERNAME_MAX = 16; // etc. } The class is big and contains LOTS of such variables. My Question: Isn't setting static variables means these variables are floating in memory all the time? Do you suggest insteading of having an abstract class, I have a instantiable class with non-static variables (just public final), so I instantiate the class and use the variables only when I need them. Or is what am I doing is completely wrong approach and you suggest something else?

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• reading root element in xml not the child

  - by Umesha MS

  Hi I am working on an application which reads XML file. Here I am trying to read the node under the not under the node . When I tried to read the I get both. Please help me to solve the problem. Bellow is the sample. "a" "x"..."/X" "b" "name" 123 "/name" "/b" "name" main "/name" "c".."/c" "/a" QDomDocument mDocument; QDomElement mDocumentElement; if (!mDocument.setContent(file.readAll())) { return ; } mDocumentElement = mDocument.documentElement(); QDomNodeList list = mDocumentElement.elementsByTagName("a").at(0).toElement().elementsByTagName("name"); int count = list.count(); for (int i = 0; i < count; i++) { QString str = list.at(i).nodeValue(); QMessageBox::information(this, "text", str, QMessageBox::Yes, 0); }

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• In C++, I want to implement a ring iterator for a deque that contains a personally defined class.

  - by George

  I have a function of a "Table" class that should add a player to the table. I decided that if the seat is taken, the function should try and go through all the seats and add the player to the next available seat. How do I implement this in my addPlayer function? int Table::addPlayer(Player player, int position) { deque<Player>::iterator it; if(playerList[position] != "(empty seat)") { //What goes here? } playerList.put(player,it); cout >> "Player " >> player.toString >> " sits at position " >> position >> endl; }

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• Mysql with innodb and serializable transaction does not (always) lock rows

  - by Tobias G.

  Hello, I have a transaction with a SELECT and possible INSERT. For concurrency reasons, I added FOR UPDATE to the SELECT. To prevent phantom rows, I'm using the SERIALIZABLE transaction isolation level. This all works fine when there are any rows in the table, but not if the table is empty. When the table is empty, the SELECT FOR UPDATE does not do any (exclusive) locking and a concurrent thread/process can issue the same SELECT FOR UPDATE without being locked. CREATE TABLE t ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, display_order INT ) ENGINE = InnoDB; SET TRANSACTION ISOLATION LEVEL SERIALIZABLE; START TRANSACTION; SELECT COALESCE(MAX(display_order), 0) + 1 from t FOR UPDATE; .. This concept works as expected with SQL Server, but not with MySQL. Any ideas on what I'm doing wrong? EDIT Adding an index on display_order does not change the behavior.

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• xcode 4 creating a 2d grid (range and domain)

  - by user1706978

  I'm learning how to program c and i'm trying to make a program the finds the range (using an equation with x as the domain) of a 2d grid...ive already attempted it, but it's giving me all these errors on Xcode, any help?(As you can see, I'm quite stuck!) #include <stdio.h> #include <stdlib.h> float domain; float domain = 2.0; float domainsol(float x ) { domain = x; float func = 1.25 * x + 5.0; return func; } int main(int argc, const char * argv[]) { }

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• assigning a string to another string

  - by user1509676

  Why this code is not running? Why str1 is not assigned to str2 ?? I know i have an option of using strcpy but i wish to know the reason why this is not working?? #include<stdio.h> int main() { char str1[]="hello"; char str2[10]; str2=str1; printf("%s",str2); return 0; } Whereas if I use pointers than it works like here.. #include<stdio.h> int main() ( char *s="good morning"; char *q; q=s; while(*q!='\0') { printf("%c",*q); q++; } return 0; } This works. Now the string has been copied via pointers so why such difference??

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• How can I optimize this code?

  - by loop0

  Hi, I'm developing a logger daemon to squid to grab the logs on a mongodb database. But I'm experiencing too much cpu utilization. How can I optimize this code? from sys import stdin from pymongo import Connection connection = Connection() db = connection.squid logs = db.logs buffer = [] a = 'timestamp' b = 'resp_time' c = 'src_ip' d = 'cache_status' e = 'reply_size' f = 'req_method' g = 'req_url' h = 'username' i = 'dst_ip' j = 'mime_type' L = 'L' while True: l = stdin.readline() if l[0] == L: l = l[1:].split() buffer.append({ a: float(l[0]), b: int(l[1]), c: l[2], d: l[3], e: int(l[4]), f: l[5], g: l[6], h: l[7], i: l[8], j: l[9] } ) if len(buffer) == 1000: logs.insert(buffer) buffer = [] if not l: break connection.disconnect()

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• What is the complexity of this c function

  - by Bunny Rabbit

  what is the complexity of the following c Function ? double foo (int n) { int i; double sum; if (n==0) return 1.0; else { sum = 0.0; for (i =0; i<n; i++) sum +=foo(i); return sum; } } Please don't just post the complexity can you help me in understanding how to go about it . EDIT: It was an objective question asked in an exam and the Options provided were 1.O(1) 2.O(n) 3.O(n!) 4.O(n^n)

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• How to convert a void pointer to array of classes

  - by user99545

  I am trying to convert a void pointer to an array of classes in a callback function that only supports a void pointer as a means of passing paramaters to the callback. class person { std::string name, age; }; void callback (void *val) { for (int i = 0; i < 9; i++) { std::cout << (person [])val[i].name; } } int main() { person p[10]; callback((void*)p); } My goal is to be able to pass an array of the class person to the callback which then prints out the data such as their name and age. However, the compile does not like what I am doing and complains that error: request for member 'name' in 'val', which is of non-class type 'void*' How can I go about doing this?

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• Strange iterator's behaviour;

  - by A-ha

  #include "stdafx.h" int _tmain(int argc, _TCHAR* argv[]) { string s = "Haven't got an idea why."; auto beg = s.begin(); auto end = s.end(); while (beg < end) { cout << *beg << '\n'; if (*beg == 'a') {//whithout if construct it works perfectly beg = s.erase(beg); } ++beg; } return 0; } Why if I erase one or more chars from this string this code breaks? I suppose it has something to do with returned iterator after erase operation being created at higher address than end iterator but I'm not sure and it surely isn't right behaviour. Or is it?

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• Why do you sometimes need to write <typename T> instead of just <T> ?

  - by StackedCrooked

  I was reading the Wikipedia article on SFINAE and encountered following code sample: struct Test { typedef int Type; }; template < typename T > void f( typename T::Type ) {} // definition #1 template < typename T > void f( T ) {} // definition #2 void foo() { f< Test > ( 10 ); //call #1 f< int > ( 10 ); //call #2 without error thanks to SFINAE } Now I've actually written code like this before, and somehow intuitively I knew that I needed to type "typename T" instead of just "T". However, it would be nice to know the actual logic behind it. Anyone care to explain?

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• "An access violation (Segmentation Fault) raised in your program."

  - by Mark

  My C++ program compiles and works up until I call this function from main(): int uword(){fstream infile("numbers.txt"); fstream exfile("wordlist.txt"); string numb[numoflines]; string lines[numoflines]; number = 1; line = 1; for(int i=0;!infile.eof();++i) { getline (infile,number); numb[i] = number; getline (exfile,line); lines[i] = line; } infile.close(); exfile.close(); string yourword; Something here causes it to crash, in the debug it pops up with "An access violation (Segmentation Fault) raised in your program."

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• C++ destructor issue with std::vector of class objects

  - by Nigel

  I am confused about how to use destructors when I have a std::vector of my class. So if I create a simple class as follows: class Test { private: int *big; public: Test () { big = new int[10000]; } ~Test () { delete [] big; } }; Then in my main function I do the following: Test tObj = Test(); vector<Test> tVec; tVec.push_back(tObj); I get a runtime crash in the destructor of Test when I go out of scope. Why is this and how can I safely free my memory?

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• How to identify each parameter type in a C# method?

  - by user465876

  I have a C# method say: MyMethod(int num, string name, Color color, MyComplexType complex) Using reflection, how can I distinctly identify each of the parameter types of any method? I want to perform some task by parameter type. If the type is simple int, string or boolean then I do something, if it is Color, XMLDocument, etc I do something else and if it is user defined type like MyComplexType or MyCalci etc then I want to do certain task. I am able to retrieve all the parameters of a method using ParameterInfo and can loop through each parameter and get their types. But how can I identify each data type? foreach (var parameter in parameters) { //identify primitive types?? //identify value types //identify reference types } Edit: this is apart of my code to create a propert grid sort of page where I want to show the parameter list with data types for the selected method. If the parameter has any userdefined type/reference type then I want to expand it further to show all the elements under it with datatypes.

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• PHP : flatten array - fastest way?

  - by Industrial

  Is there any fast way to flatten an array and select subkeys ('key'&'value' in this case) without running a foreach loop, or is the foreach always the fastest way? Array ( [0] => Array ( [key] => string [value] => a simple string [cas] => 0 ) [1] => Array ( [key] => int [value] => 99 [cas] => 0 ) [2] => Array ( [key] => array [value] => Array ( [0] => 11 [1] => 12 ) [cas] => 0 ) ) To: Array ( [int] => 99 [string] => a simple string [array] => Array ( [0] => 11 [1] => 12 ) )

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• How do I provide a string with a list of values to an "IN" statement

  - by Degan

  I am creating a string that is a list of comma-delimitted values by looping through the selections in a CheckBoxList. I am able to display this value, so I know that it is creating what I expect. I am attempting to pass this list to an IN statment in a SELECT query: SelectCommand="SELECT ThisDate, DATEPART(dw, ThisDate) AS Expr1 FROM fbCalendar WHERE (ThisDate &gt;= @ThisDate) AND (ThisDate &lt;= @ThisDate2) AND (DATEPART(dw, ThisDate) IN (@TheseDays))" <asp:ControlParameter ControlID="Label1" Name="TheseDays" PropertyName="Text" Type="String" /> This works fine as long as there is only a single item selected, but selecting a second item fails with the message: Conversion failed when converting the nvarchar value '4,5' to data type int. However, I do not understand when this would be converted to an INT. I have tried many different formatting attempts (such as encapsulating the string in parenthesis (e.g. "(4,5)" ) for the SELECT query, but I have yet to find the right one to make this work. It seems like formatting is the problem, but perhaps I am missing something else.

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• Most efficient way to Update with Linq2Sql

  - by pranay

  can I update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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• activating the class need help.... :)

  - by asm_debuger

  this is my code... i dont anderstend way the class dont work... import java.awt.BorderLayout; import java.awt.Button; import java.awt.Color; import java.awt.GridLayout; import java.awt.Panel; public class Caldesinger { public Panel p1=new Panel(); public Button[] arr=new Button[20]; public String[] name = {"9","8","7","6","5","4","3","2","1","0","+","-","*","/",".","cos","sin","=","pow"}; public Caldesinger() { for (int i = 0; i < arr.length; i++) { this.arr[i]=new Button(""+name[i]); } } public Panel getP1() { return p1; } public void setP1(Panel p1) { this.p1 = p1; } public Button[] getArr() { return arr; } public void setArr(Button[] arr) { this.arr = arr; } public Object c() { this.p1.setLayout(new GridLayout(4,15)); for (int i = 0; i < arr.length; i++) { arr[i].setBackground(Color.LIGHT_GRAY); arr[i].setForeground(Color.orange); p1.add(arr[i]); } this.p1.setLayout(new GridLayout(4,15)); return this; } } the class desinge the applet this is the main: import java.applet.Applet; import java.awt.BorderLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; public class Mainapp extends Applet implements ActionListener { Caldesinger desinge=new Caldesinger (); public void init() { this.setLayout(new BorderLayout()); this.desinge.c(); } public void ActionPerformed(ActionEvent arg0) { for (int i = 0; i <20; i++) { if(arg0.getSource()== this.desinge.arr[i]); } } } way the method c does not work? the method desinge the applet

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