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• What is the use of "Partition" keyword in MySQL?

  - by chandru_cp

  As I am a MySQL newbie. What does PARTITION mean in this MySQL statement? CREATE TABLE employees ( id INT NOT NULL, fname VARCHAR(30), lname VARCHAR(30), hired DATE NOT NULL DEFAULT '1970-01-01', separated DATE NOT NULL DEFAULT '9999-12-31', job_code INT NOT NULL, store_id INT NOT NULL ) PARTITION BY RANGE (store_id) ( PARTITION p0 VALUES LESS THAN (6), PARTITION p1 VALUES LESS THAN (11), PARTITION p2 VALUES LESS THAN (16), PARTITION p3 VALUES LESS THAN (21) );

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• Problem with joining to an empty table

  - by Imran Omar Bukhsh

  I use the following query: select * from A LEFT JOIN B on ( A.t_id != B.t_id) to get all the records in A that are not in B. The results are fine except when table B is completely empty, but then I do not get any records, even from table A. Later It wont work yet! CREATE TABLE IF NOT EXISTS T1 ( id int(11) unsigned NOT NULL AUTO_INCREMENT, title varchar(50) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL, t_id int(11) NOT NULL, PRIMARY KEY (id) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; -- -- Dumping data for table T1 INSERT INTO T1 (id, title, t_id) VALUES (1, 'apple', 1), (2, 'orange', 2); -- -- Table structure for table T2 CREATE TABLE IF NOT EXISTS T2 ( id int(11) NOT NULL AUTO_INCREMENT, title varchar(50) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL, t_id int(11) NOT NULL, PRIMARY KEY (id) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; -- -- Dumping data for table T2 INSERT INTO T2 (id, title, t_id) VALUES (1, 'dad', 2); Now I want to get all records in T1 that do not have a corresponding records in T2 I try SELECT * FROM T1 LEFT OUTER JOIN T2 ON T1.t_id != T2.t_id and it won't work

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• MACRO Question: Returning pointer to a certain value

  - by Andrei Ciobanu

  Is it possible to write a MACRO that has a type and a value as its input parameters (MACRO(type,value)), and returns a valid pointer to a location that holds the submitted value. This macro should perform like the following function, but in a more generic manner: int *val_to_ptr(int val){ int *r = NULL; r = nm_malloc(sizeof(*r)); *r = val; return r; } Where nm_malloc() is a failsafe malloc. The Macro usage should be compatible with this usage: printf("%d",*MACRO(int,5)); Is it possible to achieve that ?

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• Does std::vector change its address? How to avoid

  - by kunigami

  Since vector elements are stored contiguously, I guess it may not have the same address after some push_back's , because the initial allocated space could not suffice. I'm working on a code where I need a reference to an element in a vector, like: int main(){ vector<int> v; v.push_back(1); int *ptr = &v[0]; for(int i=2; i<100; i++) v.push_back(i); cout << *ptr << endl; //? return 0; } But it's not necessarily true that ptr contains a reference to v[0], right? How would be a good way to guarantee it? My first idea would be to use a vector of pointers and dynamic allocation. I'm wondering if there's an easier way to do that? PS.: Actually I'm using a vector of a class instead of int, but I think the issues are the same.

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• C++ assignment - stylish or performance?

  - by joejax

  Having been writing Java code for many years, I was amazed when I see this C++ statement: int a,b; int c = (a=1, b=a+2, b*3); My question is: Is this a choice of coding style, or it has real benefit? (looking for a practicle use case) I think the compiler will see it the same as following: int a=1, b=a+2; int c = b*3; (What's the offical name for this? I assume it's a standard C/C++ syntax.)

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• Mathematics errors in basic C++ program

  - by H Bomb1013

  I am working with a basic C++ program to determine the area and perimeter of a rectangle. My program works fine for whole numbers but falls apart when I use any number with a decimal. I get the impression that I am leaving something out, but since I'm a complete beginner, I have no idea what. Below is the source: #include <iostream> using namespace std; int main() { // Declared variables int length; // declares variable for length int width; // declares variable for width int area; // declares variable for area int perimeter; // declares variable for perimeter // Statements cout << "Enter the length and the width of the rectangle: "; // states what information to enter cin >> length >> width; // user input of length and width cout << endl; // closes the input area = length * width; // calculates area of rectangle perimeter = 2 * (length + width); //calculates perimeter of rectangle cout << "The area of the rectangle = " << area << " square units." <<endl; // displays the calculation of the area cout << "The perimeter of the rectangle = " << perimeter << " units." << endl; // displays the calculation of the perimeter system ("pause"); // REMOVE BEFORE RELEASE - testing purposes only return 0; }

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• How to find the largest power of 2 less than the given number

  - by nazar_art

  I need to find the largest power of 2 less than the given number. And I stuck and can't find any solution. Code: public class MathPow { public int largestPowerOf2 (int n) { int res = 2; while (res < n) { res =(int)Math.pow(res, 2); } return res; } } This doesn't work correctly. Testing output: Arguments Actual Expected ------------------------- 9 16 8 100 256 64 1000 65536 512 64 256 32 How to solve this issue?

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• Mixing C and C++, raw pointers and (boost) shared pointers

  - by oompahloompah

  I am working in C++ with some legacy C code. I have a data structure that (during initialisation), makes a copy of the structure pointed to a ptr passed to its initialisation pointer. Here is a simplification of what I am trying to do - hopefully, no important detail has been lost in the "simplification": /* C code */ typedef struct MyData { double * elems; unsigned int len; }; int NEW_mydata(MyData* data, unsigned int len) { // no error checking data->elems = (double *)calloc(len, sizeof(double)); return 0; } typedef struct Foo { MyData data data_; }; void InitFoo(Foo * foo, const MyData * the_data) { //alloc mem etc ... then assign the STRUCTURE foo.data_ = *thedata ; } C++ code ------------- typedef boost::shared_ptr<MyData> MyDataPtr; typedef std::map<std::string, MyDataPtr> Datamap; class FooWrapper { public: FooWrapper(const std::string& key) { MyDataPtr mdp = dmap[key]; InitFoo(&m_foo, const_cast<MyData*>((*mdp.get()))); } ~FooWrapper(); double get_element(unsigned int index ) const { return m_foo.elems[index]; } private: // non copyable, non-assignable FooWrapper(const FooWrapper&); FooWrapper& operator= (const FooWrapper&); Foo m_foo; }; int main(int argc, char *argv[]) { MyData data1, data2; Datamap dmap; NEW_mydata(&data1, 10); data1->elems[0] = static_cast<double>(22/7); NEW_mydata(&data2, 42); data2->elems[0] = static_cast<double>(13/21); boost::shared_ptr d1(&data1), d2(&data2); dmap["data1"] = d1; dmap["data2"] = d2; FooWrapper fw("data1"); //expect 22/7, get something else (random number?) double ret fw.get_element(0); } Essentially, what I want to know is this: Is there any reason why the data retrieved from the map is different from the one stored in the map?

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• Beginner having difficulty with SQL query

  - by Vulcanizer

  Hi, I've been studying SQL for 2 weeks now and I'm preparing for an SQL test. Anyway I'm trying to do this question: For the table: 1 create table data { 2 id int, 3 n1 int not null, 4 n2 int not null, 5 n3 int not null, 6 n4 int not null, 7 primary key (id) 8 } I need to return the relation with tuples (n1, n2, n3) where all the corresponding values for n4 are 0. The problem asks me to solve it WITHOUT using subqueries(nested selects/views) It also gives me an example table and the expected output from my query: 01 insert into data (id, n1, n2, n3, n4) 02 values (1, 2,4,7,0), 03 (2, 2,4,7,0), 04 (3, 3,6,9,8), 05 (4, 1,1,2,1), 06 (5, 1,1,2,0), 07 (6, 1,1,2,0), 08 (7, 5,3,8,0), 09 (8, 5,3,8,0), 10 (9, 5,3,8,0); expects (2,4,7) (5,3,8) and not (1,1,2) since that has a 1 in n4 in one of the cases. The best I could come up with was: 1 SELECT DISTINCT n1, n2, n3 2 FROM data a, data b 3 WHERE a.ID <> b.ID 4 AND a.n1 = b.n1 5 AND a.n2 = b.n2 6 AND a.n3 = b.n3 7 AND a.n4 = b.n4 8 AND a.n4 = 0 but I found out that also prints (1,1,2) since in the example (1,1,2,0) happens twice from IDs 5 and 6. Any suggestions would be really appreciated.

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• Customs toString in Java not giving desired output and throwing error

  - by user2972048

  I am writing a program in Java to accept and validate dates according to the Gregorian Calendar. My public boolean setDate(String aDate) function for an incorrect entry is suppose to change the boolean goodDate variable to false. That variable is suppose tell the toString function, when called, to output "Invalid Entry" but it does not. My public boolean setDate(int d, int m, int y) function works fine though. I've only included the problem parts as its a long piece of code. Thanks public boolean setDate(int day, int month, int year){ // If 1 <= day <= 31, 1 <= month <= 12, and 0 <= year <= 9999 & the day match with the month // then set object to this date and return true // Otherwise,return false (and do nothing) boolean correct = isTrueDate(day, month, year); if(correct){ this.day = day; this.month = month; this.year = year; return true; }else{ goodDate = false; return false; } //return false; } public boolean setDate(String aDate){ // If aDate is of the form "dd/mm/yyyy" or "d/mm/yyyy" // Then set the object to this date and return true. // Otherwise, return false (and do nothing) Date d = new Date(aDate); boolean correct = isTrueDate(d.day, d.month, d.year); if(correct){ this.day = d.day; this.month = d.month; this.year = d.year; return true; }else{ goodDate = false; return false; } } public String toString(){ // outputs a String of the form "dd/mm/yyyy" // where dd must be 2 digits (with leading zero if needed) // mm must be 2 digits (with leading zero if needed) // yyyy must be 4 digits (with leading zeros if needed) String day1; String month1; String year1; if(day<10){ day1 = "0" + Integer.toString(this.day); } else{ day1 = Integer.toString(this.day); } if(month<10){ month1 = "0" + Integer.toString(this.month); } else{ month1 = Integer.toString(this.month); } if(year<10){ year1 = "00" + Integer.toString(this.year); } else{ year1 = Integer.toString(this.year); } if(goodDate){ return day1 +"/" +month1 +"/" + year1; }else{ goodDate = true; return "Invalid Entry"; } } Thank you

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• Event type can't be Action<> ?

  - by Freshblood

  Hello everybody this works public event Func<int,int> createEvents; but why not this ? public event Action<int> createEvents;

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• What's the simplest way to extract the last section of an IP address?

  - by Jon Cage

  I have an IP address which I want to grab the last chunk of as an integer. So from "192.168.1.150" I'd get 150. This is the code I'd concocted (I'm using C++/CLI), but somehow it feels rather clunky: String^ ipString = "192.168.1.150"; int lastDot = ipString->LastIndexOf('.'); int lastSection = int::Parse(ipString->Substring(lastDot, ipString->Length-lastDot)); Is there a simpler way of doing this?

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• VIM plugin for updating C++ function definition

  - by Sunny

  I'm looking for a VIM plugin that can do these kind of thing. Let's say I have a function in a .cpp file void myFunction(int arg1, int arg2, int arg3){ //code } The function definition is defined in the .h file. So every time I change the function name or add a new argument to the function, I have to go back the the .h file to do the same. Is there a VIM plugin that can automate this task?

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• How to gather arbitrary length list data in ASP.NET MVC.

  - by C. Ross

  I need to gather a list of items associated with another item from my user in a ASP.NET MVC project. I would like to have a controller action like bellow. [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create(int x, int y, IEnumerable<int> zKeys) { //Do stuff here } How can I setup my form to pass data in this way? If data of this particular form can't be provided, what's the next best way to pass this type of information in ASP.NET MVC?

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• How can I do a left outer join where both tables have a where clause?

  - by cdeszaq

  Here's the scenario: I have 2 tables: CREATE TABLE dbo.API_User ( id int NOT NULL, name nvarchar(255) NOT NULL, authorization_key varchar(255) NOT NULL, is_active bit NOT NULL ) ON [PRIMARY] CREATE TABLE dbo.Single_Sign_On_User ( id int NOT NULL IDENTITY (1, 1), API_User_id int NOT NULL, external_id varchar(255) NOT NULL, user_id int NULL ) ON [PRIMARY] What I am trying to return is the following: is_active for a given authorization_key The Single_Sign_On_User.id that matches the external_id/API_User_id pair if it exists or NULL if there is no such pair When I try this query: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE Single_Sign_On_User.external_id = 'test_ext_id' AND API_User.authorization_key = 'test' where the "test" API_User record exists but the "test_ext_id" record does not, and with no other values in either table, I get no records returned. When I use: SELECT Single_Sign_On_User.id, API_User.is_active FROM API_User LEFT OUTER JOIN Single_Sign_On_User ON Single_Sign_On_User.API_User_id = API_User.id WHERE API_User.authorization_key = 'test' I get the results I expect (NULL, 1), but that query doesn't allow me to find the "test_ext_id" record if it exists but would give me all records associated with the "test" API_User record. How can I get the results I am after?

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• c++ template function compiles in header but not implementation

  - by flies

  I'm trying to learn templates and I've run into this confounding error. I'm declaring some functions in a header file and I want to make a separate implementation file where the functions will be defined. Here's the code that calls the header (dum.cpp): #include <iostream> #include <vector> #include <string> #include "dumper2.h" int main() { std::vector<int> v; for (int i=0; i<10; i++) { v.push_back(i); } test(); std::string s = ", "; dumpVector(v,s); } now, here's a working header file (dumper2.h): #include <iostream> #include <string> #include <vector> void test(); template <class T> void dumpVector( std::vector<T> v,std::string sep); template <class T> void dumpVector(std::vector<T> v, std::string sep) { typename std::vector<T>::iterator vi; vi = v.begin(); std::cout << *vi; vi++; for (;vi<v.end();vi++) { std::cout << sep << *vi ; } std::cout << "\n"; return; } with implentation (dumper2.cpp): #include <iostream> #include "dumper2.h" void test() { std::cout << "!olleh dlrow\n"; } the weird thing is that if I move the code that defines dumpVector from the .h to the .cpp file, I get the following error: g++ -c dumper2.cpp -Wall -Wno-deprecated g++ dum.cpp -o dum dumper2.o -Wall -Wno-deprecated /tmp/ccKD2e3G.o: In function `main': dum.cpp:(.text+0xce): undefined reference to `void dumpVector<int>(std::vector<int, std::allocator<int> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)' collect2: ld returned 1 exit status make: *** [dum] Error 1 So why does it work one way and not the other? Clearly the compiler can find test(), so why can't it find dumpVector?

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• C++ circular dependency - namespace vs struct

  - by Dead or Alive

  Please educate me. Why does this compile: struct compiles { struct A; struct B { B(const A &a) : member(a.member) { } int member; }; struct A { A(const B &b) : member(b.member) { } int member; }; }; while this does not: namespace doesnt { struct A; struct B { B(const A &a) : member(a.member) { } int member; }; struct A { A(const B &b) : member(b.member) { } int member; }; } (in MSVC 9.0)

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• Using template specialization in C++

  - by user550413

  How can I write a function using template specialization that has 2 different input types and an output type: template <class input1, class input2, class output> and return the sum of the 2 numbers (integers/doubles). However, if I get 2 integers I want to return an integer type but for any other combinations of integer and double I'll always return double. I am trying to do that without using directly the '+' operator but having the next functions instead: double add_double_double(double a, double b) {return (a+b);} double add_int_double(int a, double b) {return ((double)(a)+b);} int add_int_int(int a, int b) {return (a+b);}

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• Reading a variable messes it up?!?!

  - by EpsilonVector

  We have the following line of code: printf("%d\n", toc->runlist.next); printf("%d\n", toc->runlist.next); These are the definitions: typedef struct thread_overview_control{ int id[NR_UTHREADS]; list_t runlist; int active_counter; int main_thread; int need_resched; } thread_overview_control; thread_overview_control* toc; What I'm trying to do is implement user threads. For some reason the output of the above code at the point where our test run crushes is: 12345678 //some address 0 //NOW IT'S NULL?!?!?! How can this happen?? All we do is read a variable. And the strange thing is, without printf's there are no crashes. What's going on?

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• defualt parameter values in arguments and inheritance

  - by sil3nt

  Hello there, Im having trouble with some Java, How do I give in default parameter values in java?. for example I have this in c++ DVD(int i, string t, int y, string d="Unknown"): Items(i,t,y),director(d){} and in Java I tried public Dvd(int i, String t,int y, String d="Unknown"){ super(i,t,y); director = d; } which fails to build. So how do I go about giving in default values? also In my main testing class I tried giving in 3 arguments insead of 4 but this fails also. How do I get around this problem?.

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• Is there any well-known paradigm for iterating enum values?

  - by SadSido

  I have some C++ code, in which the following enum is declared: enum Some { Some_Alpha = 0, Some_Beta, Some_Gamma, Some_Total }; int array[Some_Total]; The values of Alpha, Beta and Gamma are sequential, and I gladly use the following cycle to iterate through them: for ( int someNo = (int)Some_Alpha; someNo < (int)Some_Total; ++someNo ) {} This cycle is ok, until I decide to change the order of the declarations in the enum, say, making Beta the first value and Alpha - the second one. That invalidates the cycle header, because now I have to iterate from Beta to Total. So, what are the best practices of iterating through enum? I want to iterate through all the values without changing the cycle headers every time. I can think of one solution: enum Some { Some_Start = -1, Some_Alpha, ... Some_Total }; int array[Some_Total]; and iterate from (Start + 1) to Total, but it seems ugly and I have never seen someone doing it in the code. Is there any well-known paradigm for iterating through the enum, or I just have to fix the order of the enum values? (let's pretend, I really have some awesome reasons for changing the order of the enum values)...

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• SQL Server dynamic pivot table

  - by user972255

  In SQL Server, I have two tables TableA and TableB, based on these I need to generate a report which is kind of very complex and after doing some research I come to a conclusion that I have to go with SQL Pivot table but I dont have any idea about the SQL Pivot feature so, can anyone please help me on this. Please see the details below: Create table TableA ( ProjectID INT NOT NULL, ControlID INT NOT NULL, ControlCode Varchar(2) NOT NULL, ControlPoint Decimal NULL, ControlScore Decimal NULL, ControlValue Varchar(50) ) Sample Data ------------- ProjectID | ControlID | ControlCode | ControlPoint | ControlScore | ControlValue P001 1 A 30.44 65 Invalid P001 2 C 45.30 85 Valid Create table TableB ( ControlID INT NOT NULL, ControlChildID INT NOT NULL, ControlChildValue Varchar(200) NULL ) Sample Data ------------ ControlID | ControlChildID | ControlChildValue 1 100 Yes 1 101 No 1 102 NA 1 103 Others 2 104 Yes 2 105 SomeValue Output should be in a single row for a given ProjectID with all its Control values first & followed by child control values (based on the ControlCode (i.e.) ControlCode_Child (1, 2, 3...) and it should look like this

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• Is Using Tuples in my .NET 4.0 Code a Poor Design Decision?

  - by Jason Webb

  With the addition of the Tuple class in .net 4, I have been trying to decide if using them in my design is a bad choice or not. The way I see it, a Tuple can be a shortcut to writing a result class (I am sure there are other uses too). So this: public class ResultType { public string StringValue { get; set; } public int IntValue { get; set; } } public ResultType GetAClassedValue() { //..Do Some Stuff ResultType result = new ResultType { StringValue = "A String", IntValue = 2 }; return result; } Is equivalent to this: public Tuple<string, int> GetATupledValue() { //...Do Some stuff Tuple<string, int> result = new Tuple<string, int>("A String", 2); return result; } So setting aside the possibility that I am missing the point of Tuples, is the example with a Tuple a bad design choice? To me it seems like less clutter, but not as self documenting and clean. Meaning that with the type ResultType, it is very clear later on what each part of the class means but you have extra code to maintain. With the Tuple<string, int> you will need to look up and figure out what each Item represents, but you write and maintain less code. Any experience you have had with this choice would be greatly appreciated.

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• Why does C++ behave this way?

  - by eSKay

  #include<stdio.h> int b = 0; class A { public: int a;}; class B: public A { int c; int d; public: B(){ b++; a = b; printf("B:%d\n",b); } }; int main() { A* a = new B[10]; B* b = new B[10]; printf("\n%d", a->a); a++; printf("\n%d", a->a); // prints junk value printf("\n\n%d", b->a); b++; printf("\n%d", b->a); return 0; } The second printf prints a junk value. It should figure that it is pointing to an object of type B and increment by the sizof(B). Why does that not happen?

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• Cast vector<T> to vector<const T>

  - by user345386

  I have a member variable of type vector (where is T is a custom class, but it could be int as well.) I have a function from which I want to return a pointer to this vector, but I don't want the caller to be able to change the vector or it's items. So I want the return type to be const vector* None of the casting methods I tried worked. The compiler keeps complaining that T is not compatible with const T. Here's some code that demonstrates the gist of what I'm trying to do; vector<int> a; const vector<const int>* b = (const vector<const int>* ) (&a); This code doesn't compile for me. Thanks in advance!

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