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  • how I can overcome this error C2679: binary '>>' : no operator found which takes a right-hand oper

    - by hussein abdullah
    #include <iostream> using std::cout; using std::cin; using std::endl; #include <cstring> void initialize(char[],int*); void input(const char[] ,int&); void print ( const char*,const int); void growOlder (const char [], int* ); bool comparePeople(const char* ,const int*,const char*,const int*); int main(){ char name1[25]; char name2[25]; int age1; int age2; initialize (name1,&age1); initialize (name2,&age2); print(name1,age1); print(name2,age2); input(name1,age1); input(name2,age2); print(name1,age1); print(name2,age2); growOlder(name2,&age2); if(comparePeople(name1,&age1,name2,&age2)) cout<<"Both People have the same name and age "<<endl; return 0; } void input(const char name[],int &age) { cout<<"Enter a name :"; cin>>name ; cout<<"Enter an age:"; cin>>age; cout<<endl; } void initialize ( char name[],int *age) { name[0]='\0'; *age=0; } void print ( const char name[],const int age ) { cout<<"The Value stored in variable name is :" <<name<<endl <<"The Value stored in variable age is :" <<age<<endl<<endl; } void growOlder(const char name[],int *age) { cout<< name <<" has grown one year older\n\n"; *age++; } bool comparePeople (const char *name1,const int *age1, const char *name2,const int *age2) { return(*age1==*age2 && !strcmp(name1,name2)); }

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  • operator "new" returning a non-local heap pointer for only one class ?

    - by KaluSingh Gabbar
    Language : C++ Platform : Windows Server 2003 I have an exe calling a DLL, in which when I allocate (new) the memory for class A (which is in DLL) it returns me a non-local heap pointer. I try to new other classes which are in DLL and "new" returns a valid heap pointer for them, its only Class A which is not being allocated properly. I am on windows and validating the heap by this function call : _CrtIsValidHeapPointer ( (const void *) pPtr ) I am seriously confused why this only happens with new-ing Class A and no other class ? (All Native Code)

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  • Why is there a sizeof... operator in C++0x?

    - by Motti
    I saw that @GMan implemented a version of sizeof... for variadic templates which (as far as I can tell) is equivalent to the built in sizeof.... Doesn't this go against the design principle of not adding anything to the core language if it can be implemented as a library function[citation needed]?

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  • "OR" Operator must be placed at end of previous line? (unexpected tOROP)

    - by akonsu
    I am running Ruby 1.9. This is a valid syntax: items = (data['DELETE'] || data['delete'] || data['GET'] || data['get'] || data['POST'] || data['post']) But this gives me an error: items = (data['DELETE'] || data['delete'] || data['GET'] || data['get'] || data['POST'] || data['post']) t.rb:8: syntax error, unexpected tOROP, expecting ')' || data['GET'] || data['get'] |... ^ Why?!

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  • How to make negate_unary work with any type?

    - by Chan
    Hi, Following this question: How to negate a predicate function using operator ! in C++? I want to create an operator ! can work with any functor that inherited from unary_function. I tried: template<typename T> inline std::unary_negate<T> operator !( const T& pred ) { return std::not1( pred ); } The compiler complained: Error 5 error C2955: 'std::unary_function' : use of class template requires template argument list c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 223 1 Graphic Error 7 error C2451: conditional expression of type 'std::unary_negate<_Fn1>' is illegal c:\program files\microsoft visual studio 10.0\vc\include\ostream 529 1 Graphic Error 3 error C2146: syntax error : missing ',' before identifier 'argument_type' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 4 error C2065: 'argument_type' : undeclared identifier c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 2 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 222 1 Graphic Error 6 error C2039: 'argument_type' : is not a member of 'std::basic_ostream<_Elem,_Traits>::sentry' c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 230 1 Graphic Any idea? Update Follow "templatetypedef" solution, I got new error: Error 3 error C2831: 'operator !' cannot have default parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 2 error C2808: unary 'operator !' has too many formal parameters c:\visual studio 2010 projects\graphic\graphic\main.cpp 39 1 Graphic Error 4 error C2675: unary '!' : 'is_prime' does not define this operator or a conversion to a type acceptable to the predefined operator c:\visual studio 2010 projects\graphic\graphic\main.cpp 52 1 Graphic Update 1 Complete code: #include <iostream> #include <functional> #include <utility> #include <cmath> #include <algorithm> #include <iterator> #include <string> #include <boost/assign.hpp> #include <boost/assign/std/vector.hpp> #include <boost/assign/std/map.hpp> #include <boost/assign/std/set.hpp> #include <boost/assign/std/list.hpp> #include <boost/assign/std/stack.hpp> #include <boost/assign/std/deque.hpp> struct is_prime : std::unary_function<int, bool> { bool operator()( int n ) const { if( n < 2 ) return 0; if( n == 2 || n == 3 ) return 1; if( n % 2 == 0 || n % 3 == 0 ) return 0; int upper_bound = std::sqrt( static_cast<double>( n ) ); for( int pf = 5, step = 2; pf <= upper_bound; ) { if( n % pf == 0 ) return 0; pf += step; step = 6 - step; } return 1; } }; /* template<typename T> inline std::unary_negate<T> operator !( const T& pred, typename T::argument_type* dummy = 0 ) { return std::not1<T>( pred ); } */ inline std::unary_negate<is_prime> operator !( const is_prime& pred ) { return std::not1( pred ); } template<typename T> inline void print_con( const T& con, const std::string& ms = "", const std::string& sep = ", " ) { std::cout << ms << '\n'; std::copy( con.begin(), con.end(), std::ostream_iterator<typename T::value_type>( std::cout, sep.c_str() ) ); std::cout << "\n\n"; } int main() { using namespace boost::assign; std::vector<int> nums; nums += 1, 3, 5, 7, 9; nums.erase( remove_if( nums.begin(), nums.end(), !is_prime() ), nums.end() ); print_con( nums, "After remove all primes" ); } Thanks, Chan Nguyen

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  • Calling different functions depending on the template parameter c++

    - by Noman Javed
    I want to have something like that class A { public: Array& operator()() { . . . } }; class B { public: Element& operator[](int i) { ... } }; template<class T> class execute { public: output_type = operator()(T& t) { if(T == A) Array out = T()(); else { Array res; for(int i=0 ; i < length; ++i) a[i] = t[i]; } } }; There are two issues here 1. Meta-function replacing if-else in the execute operator() 2. Return type of execute operator() Thanks in anticipation Noman

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  • Why does the right-shift operator produce a zero instead of a one?

    - by mrt181
    Hi, i am teaching myself java and i work through the exercises in Thinking in Java. On page 116, exercise 11, you should right-shift an integer through all its binary positions and display each position with Integer.toBinaryString. public static void main(String[] args) { int i = 8; System.out.println(Integer.toBinaryString(i)); int maxIterations = Integer.toBinaryString(i).length(); int j; for (j = 1; j < maxIterations; j++) { i >>= 1; System.out.println(Integer.toBinaryString(i)); } In the solution guide the output looks like this: 1000 1100 1110 1111 When i run this code i get this: 1000 100 10 1 What is going on here. Are the digits cut off? I am using jdk1.6.0_20 64bit. The book uses jdk1.5 32bit.

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  • insert ... select with divide operator in select errors?

    - by Mark
    Hi, the following query CREATE TABLE IF NOT EXISTS XY ( x INT NOT NULL , y FLOAT NULL , PRIMARY KEY(x) ) INSERT INTO XY (x,y) (select 1 as x ,(1/7) as y); errors with Error code 1064, SQL state 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INSERT INTO XY (x,y) (select 1 as x ,(1/7) as y)' at line 7 Line 1, column 1 any ideas?

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  • Is there a .NET class that represents operator types?

    - by user323774
    I would like to do the following: *OperatorType* o = *OperatorType*.GreaterThan; int i = 50; int increment = -1; int l = 0; for(i; i o l; i = i + increment) { //code } this concept can be kludged in javascript using an eval()... but this idea is to have a loop that can go forward or backward based on values set at runtime. is this possible? Thanks

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  • Why does the assignment operator return a value and not a reference?

    - by Nick Lowman
    I saw the example below explained on this site and thought both answers would be 20 and not the 10 that is returned. He wrote that both the comma and assignment returns a value, not a reference. I don't quite understand what that means. I understand it in relation to passing variables into functions or methods i.e primitive types are passed in by value and objects by reference but I'm not sure how it applies in this case. I also understand about context and the value of 'this' (after help from stackoverflow) but I thought in both cases I would still be invoking it as a method, foo.bar() which would mean foo is the context but it seems both result in a function call bar(). Why is that and what does it all mean? var x = 10; var foo = { x: 20, bar: function () {return this.x;} }; (foo.bar = foo.bar)();//returns 10 (foo.bar, foo.bar)();//returns 10

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  • is the + in += on a Map a prefix operator of =?

    - by Steve
    In the book "Programming in Scala" from Martin Odersky there is a simple example in the first chapter: var capital = Map("US" -> "Washington", "France" -> "Paris") capital += ("Japan" -> "Tokyo") The second line can also be written as capital = capital + ("Japan" -> "Tokyo") I am curious about the += notation. In the class Map, I didn't found a += method. I was able to the same behaviour in an own example like class Foo() { def +(value:String) = { println(value) this } } object Main { def main(args: Array[String]) = { var foo = new Foo() foo = foo + "bar" foo += "bar" } } I am questioning myself, why the += notation is possible. It doesn't work if the method in the class Foo is called test for example. This lead me to the prefix notation. Is the + a prefix notation for the assignment sign (=)? Can somebody explain this behaviour?

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  • How to skip an empty LIKE operator in a multiple LIKE query?

    - by alex
    I notice my query doesn't behave correctly if one of the like variables is empty: SELECT name FROM employee WHERE name LIKE '%a%' AND color LIKE '%A%' AND city LIKE '%b%' AND country LIKE '%B%' AND sport LIKE '%c%' AND hobby LIKE '%C%' Now when a and A are not empty it works but when a, A and c are not empty the c part is not excuted so it seems? How can I fix this?

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  • C# performance of static string[] contains() (slooooow) vs. == operator

    - by Andrew White
    Hiya, Just a quick query: I had a piece of code which compared a string against a long list of values, e.g. if(str == "string1" || str = "string2" || str == "string3" || str = "string4". DoSomething(); And the interest of code clarity and maintainability I changed it to public static string[] strValues = { "String1", "String2", "String3", "String4"}; ... if(strValues.Contains(str) DoSomething(); Only to find the code execution time went from 2.5secs to 6.8secs (executed ca. 200,000 times). I certainly understand a slight performance trade off, but 300%? Anyway I could define the static strings differently to enhance performance? Cheers.

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  • Javascript === vs == : Does it matter which "equal" operator I use?

    - by bcasp
    I'm using JSLint to go through some horrific JavaScript at work and it's returning a huge number of suggestions to replace == with === when doing things like comparing 'idSele_UNVEHtype.value.length == 0' inside of an if statement. I'm basically wondering if there is a performance benefit to replacing == with ===. Any performance improvement would probably be welcomed as there are hundreds (if not thousands) of these comparison operators being used throughout the file. I tried searching for relevant information to this question, but trying to search for something like '=== vs ==' doesn't seem to work so well with search engines...

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  • Why would you use the ternary operator without assigning a value for the "true" condition?

    - by RickNotFred
    In the Android open-source qemu code I ran across this line of code: machine->max_cpus = machine->max_cpus ?: 1; /* Default to UP */ It this just a confusing way of saying: if (machine->max_cpus) { ; //do nothing } else { machine->max_cpus = 1; } If so, wouldn't it be clearer as: if (machine->max_cpus == 0) machine->max_cpus = 1; Interestingly, this compiles and works fine with gcc, but doesn't compile on http://www.comeaucomputing.com/tryitout/ .

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  • Is it bad practice to make an iterator that is aware of its own end

    - by aaronman
    For some background of why I am asking this question here is an example. In python the method chain chains an arbitrary number of ranges together and makes them into one without making copies. Here is a link in case you don't understand it. I decided I would implement chain in c++ using variadic templates. As far as I can tell the only way to make an iterator for chain that will successfully go to the next container is for each iterator to to know about the end of the container (I thought of a sort of hack in where when != is called against the end it will know to go to the next container, but the first way seemed easier and safer and more versatile). My question is if there is anything inherently wrong with an iterator knowing about its own end, my code is in c++ but this can be language agnostic since many languages have iterators. #ifndef CHAIN_HPP #define CHAIN_HPP #include "iterator_range.hpp" namespace iter { template <typename ... Containers> struct chain_iter; template <typename Container> struct chain_iter<Container> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end;//never really used but kept it for consistency public: chain_iter(Container & container, bool is_end=false) : begin(container.begin()),end(container.end()) { if(is_end) begin = container.end(); } chain_iter & operator++() { ++begin; return *this; } auto operator*()->decltype(*begin) { return *begin; } bool operator!=(const chain_iter & rhs) const{ return this->begin != rhs.begin; } }; template <typename Container, typename ... Containers> struct chain_iter<Container,Containers...> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end; bool end_reached = false; chain_iter<Containers...> next_iter; public: chain_iter(Container & container, Containers& ... rest, bool is_end=false) : begin(container.begin()), end(container.end()), next_iter(rest...,is_end) { if(is_end) begin = container.end(); } chain_iter & operator++() { if (begin == end) { ++next_iter; } else { ++begin; } return *this; } auto operator*()->decltype(*begin) { if (begin == end) { return *next_iter; } else { return *begin; } } bool operator !=(const chain_iter & rhs) const { if (begin == end) { return this->next_iter != rhs.next_iter; } else return this->begin != rhs.begin; } }; template <typename ... Containers> iterator_range<chain_iter<Containers...>> chain(Containers& ... containers) { auto begin = chain_iter<Containers...>(containers...); auto end = chain_iter<Containers...>(containers...,true); return iterator_range<chain_iter<Containers...>>(begin,end); } } #endif //CHAIN_HPP

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  • Objective-C scanf spaces issue

    - by Rob
    I am learning objective-C and for the life of me can't figure out why this is happening. When the user inputs when the code is: scanf("%c %lf", &operator, &number); For some reason it messes with this code: doQuit = 0; [deskCalc setAccumulator: 0]; while (doQuit == 0) { NSLog(@"Please input an operation and then a number:"); scanf("%c %lf", &operator, &number); switch (operator) { case '+': [deskCalc add: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '-': [deskCalc subtract: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '*': case 'x': [deskCalc multiply: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case '/': if (number == 0) NSLog(@"You can't divide by zero."); else [deskCalc divide: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case 'S': [deskCalc setAccumulator: number]; NSLog (@"%lf", [deskCalc accumulator]); break; case 'E': doQuit = 1; break; default: NSLog(@"You did not enter a valid operator."); break; } } When the user inputs for example "E 10" it will exit the loop but it will also print "You did not enter a valid operator." When I change the code to: scanf(" %c %lf", &operator, &number); It all of a sudden doesn't print this last line. What is it about the space before %c that fixes this?

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  • Why we can't we overload "=" using friend function?

    - by ashish-sangwan
    Why it is not allowed to overload "=" using friend function? I have written a small program but it is giving error. class comp { int real; int imaginary; public: comp(){real=0; imaginary=0;} void show(){cout << "Real="<<real<<" Imaginary="<<imaginary<<endl;} void set(int i,int j){real=i;imaginary=j;} friend comp operator=(comp &op1,const comp &op2); }; comp operator=(comp &op1,const comp &op2) { op1.imaginary=op2.imaginary; op1.real=op2.real; return op1; } int main() { comp a,b; a.set(10,20); b=a; b.show(); return 0; } The compilation gives the following error :- [root@dogmatix stackoverflow]# g++ prog4.cpp prog4.cpp:11: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp:14: error: ‘comp operator=(comp&, const comp&)’ must be a nonstatic member function prog4.cpp: In function ‘int main()’: prog4.cpp:25: error: ambiguous overload for ‘operator=’ in ‘b = a’ prog4.cpp:4: note: candidates are: comp& comp::operator=(const comp&) prog4.cpp:14: note: comp operator=(comp&, const comp&)

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  • C++ overloading comparative operators for a MyString class

    - by Taylor Gang
    bool operator == (const MyString& left, const MyString& right) { if(left.value == right.value) return true; else return false; } bool operator != (const MyString& left, const MyString& right) { if(left == right) return false; else return true; } bool operator < (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == -1) return true; else return false; } bool operator > (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == 1) return true; else return false; } bool operator <= (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == -1 || strcmp(left.value, right.value) == 0) return true; else return false; } bool operator >= (const MyString& left, const MyString& right) { if(strcmp(left.value, right.value) == 1 || strcmp(left.value, right.value) == 0) return true; else return false; } So these are my implemented comparison operators for my MyString class, they fail the test program that my professor gave me and could use some direction. Thanks in advance for any and all help I receive.

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  • C++ unrestricted union workaround

    - by Chris
    #include <stdio.h> struct B { int x,y; }; struct A : public B { // This whines about "copy assignment operator not allowed in union" //A& operator =(const A& a) { printf("A=A should do the exact same thing as A=B\n"); } A& operator =(const B& b) { printf("A = B\n"); } }; union U { A a; B b; }; int main(int argc, const char* argv[]) { U u1, u2; u1.a = u2.b; // You can do this and it calls the operator = u1.a = (B)u2.a; // This works too u1.a = u2.a; // This calls the default assignment operator >:@ } Is there any workaround to be able to do that last line u1.a = u2.a with the exact same syntax, but have it call the operator = (don't care if it's =(B&) or =(A&)) instead of just copying data? Or are unrestricted unions (not supported even in Visual Studio 2010) the only option?

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