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• What is the purpose of Java's unary plus operator?

  - by Syntactic

  Java's unary plus operator appears to have come over from C, via C++. As near as I can tell, it has the following effects: promotes its operand to int, if it's not already an int or wider unboxes its operand, if it's a wrapper object complicates slightly the parsing of evil expressions containing large numbers of consecutive plus signs It seems to me that there are better (or, at least, clearer) ways to do all of these things. In this SO question, concerning the counterpart operator in C#, someone said that "It's there to be overloaded if you feel the need." But in Java, one cannot overload any operator. So does this operator exist in Java just because it existed in C++?

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• In what situation should the built-in 'operator' module be used in python?

  - by apphacker

  I'm speaking of this module: http://docs.python.org/library/operator.html From the article: The operator module exports a set of functions implemented in C corresponding to the intrinsic operators of Python. For example, operator.add(x, y) is equivalent to the expression x+y. The function names are those used for special class methods; variants without leading and trailing __ are also provided for convenience. I'm not sure I understand the benefit or purpose of this module.

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• Has anyone found the need to declare the return parameter of a copy assignment operator const?

  - by Keith

  The copy assignment operator has the usual signature: my_class & operator = (my_class const & rhs); Does the following signature have any practical use? my_class const & operator = (my_class const & rhs); You can only define one or the other, but not both.

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• C# Extend array type to overload operators

  - by Episodex

  I'd like to create my own class extending array of ints. Is that possible? What I need is array of ints that can be added by "+" operator to another array (each element added to each), and compared by "==", so it could (hopefully) be used as a key in dictionary. The thing is I don't want to implement whole IList interface to my new class, but only add those two operators to existing array class. I'm trying to do something like this: class MyArray : Array<int> But it's not working that way obviously ;). Sorry if I'm unclear but I'm searching solution for hours now... UPDATE: I tried something like this: class Zmienne : IEquatable<Zmienne> { public int[] x; public Zmienne(int ilosc) { x = new int[ilosc]; } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) { return false; } return base.Equals((Zmienne)obj); } public bool Equals(Zmienne drugie) { if (x.Length != drugie.x.Length) return false; else { for (int i = 0; i < x.Length; i++) { if (x[i] != drugie.x[i]) return false; } } return true; } public override int GetHashCode() { int hash = x[0].GetHashCode(); for (int i = 1; i < x.Length; i++) hash = hash ^ x[i].GetHashCode(); return hash; } } Then use it like this: Zmienne tab1 = new Zmienne(2); Zmienne tab2 = new Zmienne(2); tab1.x[0] = 1; tab1.x[1] = 1; tab2.x[0] = 1; tab2.x[1] = 1; if (tab1 == tab2) Console.WriteLine("Works!"); And no effect. I'm not good with interfaces and overriding methods unfortunately :(. As for reason I'm trying to do it. I have some equations like: x1 + x2 = 0.45 x1 + x4 = 0.2 x2 + x4 = 0.11 There are a lot more of them, and I need to for example add first equation to second and search all others to find out if there is any that matches the combination of x'es resulting in that adding. Maybe I'm going in totally wrong direction?

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• Why is Perl's smart-match operator considered broken?

  - by Sean McMillan

  I've seen a number of comments across the web Perl's smart-match operator is broken. I know it originally was part of Perl 6, then was implemented in Perl 5.10 off of an old version of the spec, and was then corrected in 5.10.1 to match the current Perl 6 spec. Is the problem fixed in 5.10.1+, or are there other problems with the smart-match operator that make it troublesome in practice? What are the problems? Is there a yet-more-updated version (Perl 6, perhaps) that fixes the problems?

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• Undocumented Gmail Search Operator Ferrets Out Large Email Attachments

  - by Jason Fitzpatrick

  If you’re looking for a way to quickly find large email attachments in your Gmail account, this undocumented search operator makes it simple to zero in on the hulking attachments hiding out in your inbox. To use the search operator simply plug in “size:” and some value to narrow your search to only emails that size or larger. In the screenshot above we searched for “size:20000000″ to search for files roughly 20MB or larger (if you want to be extremely precise, a true 20MB search would be “size:20971520″). If you’re looking to clean up your Gmail account this is a nearly zero-effort way to find the biggest space hogs–in our case, we found an email packed with massive PDF files from a 5 year old project that we were more than happy to purge. Finding Large Attachments in Google Mail/Gmail [via gHacks] 6 Ways Windows 8 Is More Secure Than Windows 7 HTG Explains: Why It’s Good That Your Computer’s RAM Is Full 10 Awesome Improvements For Desktop Users in Windows 8

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• Why would one overload the && and & operator?

  - by acidzombie24

  The same question goes for | and ||. Why would one overload or 'use' the & and && operator? The only use i thought of are Bitwise Ands for int base types (but not float/decimals) using & logical short circuit for bools/functions that return bool. Using the && operator usually. I cant think of any classes that use those operators. Absolutely none. I know a class might support + (and not '-') which combine two strings together. I seen an object such as datetime overload '-' so two dates can be subtracted to make a timespan (obviously you cant add two dates) but i never seen &, &&, | and || used. Does anyone know of a use? In any language?

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• Null Values And The T-SQL IN Operator

  - by Jesse

  I came across some unexpected behavior while troubleshooting a failing test the other day that took me long enough to figure out that I thought it was worth sharing here. I finally traced the failing test back to a SELECT statement in a stored procedure that was using the IN t-sql operator to exclude a certain set of values. Here’s a very simple example table to illustrate the issue: Customers CustomerId INT, NOT NULL, Primary Key CustomerName nvarchar(100) NOT NULL SalesRegionId INT NULL   The ‘SalesRegionId’ column contains a number representing the sales region that the customer belongs to. This column is nullable because new customers get created all the time but assigning them to sales regions is a process that is handled by a regional manager on a periodic basis. For the purposes of this example, the Customers table currently has the following rows: CustomerId CustomerName SalesRegionId 1 Customer A 1 2 Customer B NULL 3 Customer C 4 4 Customer D 2 5 Customer E 3   How could we write a query against this table for all customers that are NOT in sales regions 2 or 4? You might try something like this: 1: SELECT 2: CustomerId, 3: CustomerName, 4: SalesRegionId 5: FROM Customers 6: WHERE SalesRegionId NOT IN (2,4)   Will this work? In short, no; at least not in the way that you might expect. Here’s what this query will return given the example data we’re working with: CustomerId CustomerName SalesRegionId 1 Customer A 1 5 Customer E 5   I was expecting that this query would also return ‘Customer B’, since that customer has a NULL SalesRegionId. In my mind, having a customer with no sales region should be included in a set of customers that are not in sales regions 2 or 4.When I first started troubleshooting my issue I made note of the fact that this query should probably be re-written without the NOT IN clause, but I didn’t suspect that the NOT IN clause was actually the source of the issue. This particular query was only one minor piece in a much larger process that was being exercised via an automated integration test and I simply made a poor assumption that the NOT IN would work the way that I thought it should. So why doesn’t this work the way that I thought it should? From the MSDN documentation on the t-sql IN operator: If the value of test_expression is equal to any value returned by subquery or is equal to any expression from the comma-separated list, the result value is TRUE; otherwise, the result value is FALSE. Using NOT IN negates the subquery value or expression. The key phrase out of that quote is, “… is equal to any expression from the comma-separated list…”. The NULL SalesRegionId isn’t included in the NOT IN because of how NULL values are handled in equality comparisons. From the MSDN documentation on ANSI_NULLS: The SQL-92 standard requires that an equals (=) or not equal to (<>) comparison against a null value evaluates to FALSE. When SET ANSI_NULLS is ON, a SELECT statement using WHERE column_name = NULL returns zero rows even if there are null values in column_name. A SELECT statement using WHERE column_name <> NULL returns zero rows even if there are nonnull values in column_name. In fact, the MSDN documentation on the IN operator includes the following blurb about using NULL values in IN sub-queries or expressions that are used with the IN operator: Any null values returned by subquery or expression that are compared to test_expression using IN or NOT IN return UNKNOWN. Using null values in together with IN or NOT IN can produce unexpected results. If I were to include a ‘SET ANSI_NULLS OFF’ command right above my SELECT statement I would get ‘Customer B’ returned in the results, but that’s definitely not the right way to deal with this. We could re-write the query to explicitly include the NULL value in the WHERE clause: 1: SELECT 2: CustomerId, 3: CustomerName, 4: SalesRegionId 5: FROM Customers 6: WHERE (SalesRegionId NOT IN (2,4) OR SalesRegionId IS NULL)   This query works and properly includes ‘Customer B’ in the results, but I ultimately opted to re-write the query using a LEFT OUTER JOIN against a table variable containing all of the values that I wanted to exclude because, in my case, there could potentially be several hundred values to be excluded. If we were to apply the same refactoring to our simple sales region example we’d end up with: 1: DECLARE @regionsToIgnore TABLE (IgnoredRegionId INT) 2: INSERT @regionsToIgnore values (2),(4) 3:  4: SELECT 5: c.CustomerId, 6: c.CustomerName, 7: c.SalesRegionId 8: FROM Customers c 9: LEFT OUTER JOIN @regionsToIgnore r ON r.IgnoredRegionId = c.SalesRegionId 10: WHERE r.IgnoredRegionId IS NULL By performing a LEFT OUTER JOIN from Customers to the @regionsToIgnore table variable we can simply exclude any rows where the IgnoredRegionId is null, as those represent customers that DO NOT appear in the ignored regions list. This approach will likely perform better if the number of sales regions to ignore gets very large and it also will correctly include any customers that do not yet have a sales region.

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• Template inheritence c++

  - by Chris Condy

  I have made a template singleton class, I have also made a data structure that is templated. My question is; how do I make my templated data structure inherit from a singleton so you can only have one float type of this structure? I have tested both seperate and have found no problems. Code provided under... (That is the problem) template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > The problem is the code above doesn't work I get alot of errors. I cant get it to no matter what I do template a templated singleton class... I was asking for maybe advice or maybe if the code above is incorrect guidence? #ifndef SINGLETON_H #define SINGLETON_H template <class Type> class Singleton { public: virtual ~Singleton(); Singleton(); static Type* m_instance; }; template <class Type> Type* Singleton<Type>::m_instance = 0; #include "Singleton.cpp" #endif #ifndef SINGLETON_CPP #define SINGLETON_CPP #include "Singleton.h" template <class Type> Singleton<Type>::Singleton() { } template <class Type> Singleton<Type>::~Singleton() { } template <class Type> Type* Singleton<Type>::getInstance() { if(m_instance==nullptr) { m_instance = new Type; } return m_instance; } #endif #ifndef ABSTRACTRMANAGERS_H #define ABSTRACTRMANAGERS_H #include <vector> #include <map> #include <stack> #include "Singleton.h" template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > { public: virtual ~AbstractRManagers(); int insert(Type* type, std::string name); Type* remove(int i); Type* remove(std::string name); Type* get(int i); Type* getS(std::string name); int get(std::string name); int get(Type* i); bool check(std::string name); int resourceSize(); protected: private: std::vector<Type*> m_resources; std::map<std::string,int> m_map; std::stack<int> m_freePos; }; #include "AbstractRManagers.cpp" #endif #ifndef ABSTRACTRMANAGERS_CPP #define ABSTRACTRMANAGERS_CPP #include "AbstractRManagers.h" template <class Type> int AbstractRManagers<Type>::insert(Type* type, std::string name) { int i=0; if(!check(name)) { if(m_freePos.empty()) { m_resources.push_back(type); i = m_resources.size()-1; m_map[name] = i; } else { i = m_freePos.top(); m_freePos.pop(); m_resources[i] = type; m_map[name] = i; } } else i = -1; return i; } template <class Type> int AbstractRManagers<Type>::resourceSize() { return m_resources.size(); } template <class Type> bool AbstractRManagers<Type>::check(std::string name) { std::map<std::string,int>::iterator it; it = m_map.find(name); if(it==m_map.end()) return false; return true; } template <class Type> Type* AbstractRManagers<Type>::remove(std::string name) { Type* temp = m_resources[m_map[name]]; if(temp!=NULL) { std::map<std::string,int>::iterator it; it = m_map[name]; m_resources[m_map[name]] = NULL; m_freePos.push(m_map[name]); delete (*it).second; delete (*it).first; return temp; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::remove(int i) { if((i < m_resources.size())&&(i > 0)) { Type* temp = m_resources[i]; m_resources[i] = NULL; m_freePos.push(i); std::map<std::string,int>::iterator it; for(it=m_map.begin();it!=m_map.end();it++) { if((*it).second == i) { delete (*it).second; delete (*it).first; return temp; } } return temp; } return NULL; } template <class Type> int AbstractRManagers<Type>::get(Type* i) { for(int i2=0;i2<m_resources.size();i2++) { if(i == m_resources[i2]) { return i2; } } return -1; } template <class Type> Type* AbstractRManagers<Type>::get(int i) { if((i < m_resources.size())&&(i >= 0)) { return m_resources[i]; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::getS(std::string name) { return m_resources[m_map[name]]; } template <class Type> int AbstractRManagers<Type>::get(std::string name) { return m_map[name]; } template <class Type> AbstractRManagers<Type>::~AbstractRManagers() { } #endif #include "AbstractRManagers.h" struct b { float x; }; int main() { b* a = new b(); AbstractRManagers<b>::getInstance()->insert(a,"a"); return 0; } This program produces next errors when compiled : 1> main.cpp 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1> c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(124) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const' 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(71) : see reference to class template instantiation 'std::less<_Ty>' being compiled 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(451) : see reference to class template instantiation 'std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,_Mfl>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int, 1> _Pr=std::less<std::string>, 1> _Alloc=std::allocator<std::pair<const std::string,int>>, 1> _Mfl=false 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(520) : see reference to class template instantiation 'std::_Tree_nod<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(659) : see reference to class template instantiation 'std::_Tree_val<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(81) : see reference to class template instantiation 'std::_Tree<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(28) : see reference to class template instantiation 'std::map<_Kty,_Ty>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(30) : see reference to class template instantiation 'AbstractRManagers<Type>' being compiled 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2676: binary '<' : 'const std::string' does not define this operator or a conversion to a type acceptable to the predefined operator ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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• Is it good practice to use the XOR (^) operator in Java for boolean checks?

  - by Pete

  I personally like the 'exclusive or' operator when it makes sense in context of boolean checks because of its conciseness. I much prefer to write if (boolean1 ^ boolean2) { //do it } than if((boolean1 && !boolean2) || (boolean2 && !boolean1)) { //do it } but I often get confused looks (from other experienced java developers, not just the newbies), and sometimes comments about how it should only be used for bitwise operations. I'm curious as to the best practices others use around the '^' operator.

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• When I overload the assignment operator for my simple class array, I get the wrong answer I espect

  - by user299648

  //output is "01234 00000" but the output should be or what I want it to be is // "01234 01234" because of the assignment overloaded operator #include <iostream> using namespace std; class IntArray { public: IntArray() : size(10), used(0) { a= new int[10]; } IntArray(int s) : size(s), used(0) { a= new int[s]; } int& operator[]( int index ); IntArray& operator =( const IntArray& rightside ); ~IntArray() { delete [] a; } private: int *a; int size; int used;//for array position }; int main() { IntArray copy; if( 2>1) { IntArray arr(5); for( int k=0; k<5; k++) arr[k]=k; copy = arr; for( int j=0; j<5; j++) cout<<arr[j]; } cout<<" "; for( int j=0; j<5; j++) cout<<copy[j]; return 0; } int& IntArray::operator[]( int index ) { if( index >= size ) cout<<"ilegal index in IntArray"<<endl; return a[index]; } IntArray& IntArray::operator =( const IntArray& rightside ) { if( size != rightside.size )//also checks if on both side same object { delete [] a; a= new int[rightside.size]; } size=rightside.size; used=rightside.used; for( int i = 0; i < used; i++ ) a[i]=rightside.a[i]; return *this; }

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• Assigning a vector of one type to a vector of another type

  - by deworde

  Hi, I have an "Event" class. Due to the way dates are handled, we need to wrap this class in a "UIEvent" class, which holds the Event, and the date of the Event in another format. What is the best way of allowing conversion from Event to UIEvent and back? I thought overloading the assignment or copy constructor of UIEvent to accept Events (and vice versa)might be best.

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• == and === operators in php

  - by Lizard

  Lets say I have a variable that will always be a string. Now take the code below: if($myVar === "teststring") Note $myVar will always be a string, so my questions is Which is quicker/best, using === (Indentity) or the == (Equality)?

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• Changing the cell range of conditional formatting in LibreOffice Calc

  - by Simon Lundberg

  Is there any way of changing the range of conditional formatting in LibreOffice Calc (version 3.6)? I have a set applied already to a range of cells, but there is no obvious way of changing which cells a given set of conditional formatting is applied to. I either have to copy and paste the formatting, which results in multiple entries in the conditional formatting (which makes it difficult to manage), or delete the entire thing and create a new one every single time I want to change the range of cells. Is there a better way? link to screenshot

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• Other ternary operators besides ternary conditional (?:)

  - by Malcolm

  The "ternary operator" expression is now almost equivalent to the ternary conditional operator: condition ? trueExpression : falseExpression; However, "ternary operator" only means that it takes three arguments. I'm just curious, are there any languages with any other built-in ternary operators besides conditional operator and which ones?

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• Is calling of overload operator-> resolved at compile time?

  - by Brent

  when I tried to compile the code: (note: func and func2 is not typo) struct S { void func2() {} }; class O { public: inline S* operator->() const; private: S* ses; }; inline S* O::operator->() const { return ses; } int main() { O object; object->func(); return 0; } there is a compile error reported: D:\code>g++ operatorp.cpp -S -o operatorp.exe operatorp.cpp: In function `int main()': operatorp.cpp:27: error: 'struct S' has no member named 'func' it seems that invoke the overloaded function of "operator-" is done during compile time? I'd added "-S" option for compile only.

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• Is it possible to supply template parameters when calling operator()?

  - by Paul

  I'd like to use a template operator() but am not sure if it's possible. Here is a simple test case that won't compile. Is there something wrong with my syntax, or is this simply not possible? struct A { template<typename T> void f() { } template<typename T> void operator()() { } }; int main() { A a; a.f<int>(); // This compiles. a.operator()<int>(); // This compiles. a<int>(); // This won't compile. return 0; }

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• Showplan Operator of the Week - Compute Scalar

  The third part of Fabiano's mission to describe the major Showplan Operators used by SQL Server's Query Optimiser continues with the 'Compute Scalar' operator. Fabiano shows how a tweak to SQL to avoid a 'Compute Scalar' step can improve its performance.

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• Showplan Operator of the Week - Lazy Spool

  Continuing to illuminate the depths of SQL Server's Query Optimizer, Fabiano shines a light on the sixth major Showplan Operator on his list: the Lazy Spool. What does the Lazy Spool do that's so special, how does the Query Optimizer use it, and why is it so Lazy? Fabiano explains all...

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• Showplan Operator of the Week - Merge Interval

  When Fabiano agreed to undertake the epic task of describing each showplan operator, none of us quite predicted the interesting ways that the series helps to understand how the query optimizer works. With the Merge Interval, Fabiano comes up with some insights about the way that the Query optimizer handles overlapping ranges efficiently. Free trial of SQL Backup™“SQL Backup was able to cut down my backup time significantly AND achieved a 90% compression at the same time!” Joe Cheng. Download a free trial now.

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• Showplan Operator of the Week - Concatenation

  Fabiano continues in his mission to describe, one week at a time, all the major Showplan Operators used by SQL Server's Query Optimiser to build the Query Plan. This week he gets the Concatenation operator .

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• Showplan Operator of the Week - Concatenation

  Fabiano continues in his mission to describe, one week at a time, all the major Showplan Operators used by SQL Server's Query Optimiser to build the Query Plan. This week he gets the Concatenation operator ....Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• C# Algorithms for * Operator

  - by Harsha

  I was reading up on Algorithms and came across the Karatsuba multiplication algorithm and a little wiki-ing led to the Schonhage-Strassen and Furer algorithms for multiplication. I was wondering what algorithms are used on the * operator in C#? While multiplying a pair of integers or doubles, does it use a combination of algorithms with some kind of strategy based on the size of the numbers? How could I find out the implementation details for C#?

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• ShowPlan Operator of the Week - Merge Join

  Did you ever wonder how and why your indexes affect the performances of joins? Once you've read Fabiano Amorim's unforgettable explanation, you'll learn to love the MERGE operator, and plan your indexes so as to allow the Query Optimiser to use it. Free trial of SQL Backup™“SQL Backup was able to cut down my backup time significantly AND achieved a 90% compression at the same time!” Joe Cheng. Download a free trial now.

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• Physical Join Operators in SQL Server - Merge Operator

  In Part I of this series on physical join operators we looked at Nested Loops. We now turn our attention to the Merge operator. For this article series I am using an analogy of two sets ... [Read Full Article]

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