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  • conditional operator in C question

    - by Seephor
    I just have a quick question about the conditional operator. Still a budding programmer here. I am given x = 1, y = 2, and z = 3. I want to know, why after this statement: y += x-- ? z++ : --z; That y is 5. The values after the statement are x = 0, y = 5, and z = 4. I know the way the conditional operator works is that it is formatted like this: variable = condition ? value if true : value if false. For the condition, y += x-- , how does y become 5? I can only see 2 (2 += 0) and 3 (2 += 1)(then x-- becomes zero) as possibilities. Any help is much appreciated. :)

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  • What do you think about ??= operator in C#?

    - by TN
    Do you think that C# will support something like ??= operator? Instead of this: if (list == null) list = new List<int>(); It might be possible to write: list ??= new List<int>(); Now, I could use (but it seems to me not well readable): list = list ?? new List<int>();

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  • Java conditional operator ?: result type

    - by Wangnick
    I'm a bit puzzled about the conditional operator. Consider the following two lines: Float f1 = false? 1.0f: null; Float f2 = false? 1.0f: false? 1.0f: null; Why does f1 become null and the second statement throws a NullPointerException? Langspec-3.0 para 15.25 sais: Otherwise, the second and third operands are of types S1 and S2 respectively. Let T1 be the type that results from applying boxing conversion to S1, and let T2 be the type that results from applying boxing conversion to S2. The type of the conditional expression is the result of applying capture conversion (§5.1.10) to lub(T1, T2) (§15.12.2.7). So for false?1.0f:null T1 is Float and T2 is the null type. But what is the result of lub(T1,T2)? This para 15.12.2.7 is just a bit too much ... BTW, I'm using 1.6.0_18 on Windows. PS: I know that Float f2 = false? (Float) 1.0f: false? (Float) 1.0f: null; doesn't throw NPE.

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  • C++ Operator Ambiguity

    - by Scott
    Forgive me, for I am fairly new to C++, but I am having some trouble regarding operator ambiguity. I think it is compiler-specific, for the code compiled on my desktop. However, it fails to compile on my laptop. I think I know what's going wrong, but I don't see an elegant way around it. Please let me know if I am making an obvious mistake. Anyhow, here's what I'm trying to do: I have made my own vector class called Vector4 which looks something like this: class Vector4 { private: GLfloat vector[4]; ... } Then I have these operators, which are causing the problem: operator GLfloat* () { return vector; } operator const GLfloat* () const { return vector; } GLfloat& operator [] (const size_t i) { return vector[i]; } const GLfloat& operator [] (const size_t i) const { return vector[i]; } I have the conversion operator so that I can pass an instance of my Vector4 class to glVertex3fv, and I have subscripting for obvious reasons. However, calls that involve subscripting the Vector4 become ambiguous to the compiler: enum {x, y, z, w} Vector4 v(1.0, 2.0, 3.0, 4.0); glTranslatef(v[x], v[y], v[z]); Here are the candidates: candidate 1: const GLfloat& Vector4:: operator[](size_t) const candidate 2: operator[](const GLfloat*, int) <built-in> Why would it try to convert my Vector4 to a GLfloat* first when the subscript operator is already defined on Vector4? Is there a simple way around this that doesn't involve typecasting? Am I just making a silly mistake? Thanks for any help in advance.

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  • Ternary operator in VB.NET

    - by Jalpesh P. Vadgama
    We all know about Ternary operator in C#.NET. I am a big fan of ternary operator and I like to use it instead of using IF..Else. Those who don’t know about ternary operator please go through below link. http://msdn.microsoft.com/en-us/library/ty67wk28(v=vs.80).aspx Here you can see ternary operator returns one of the two values based on the condition. See following example. bool value = false;string output=string.Empty;//using If conditionif (value==true) output ="True";else output="False";//using tenary operatoroutput = value == true ? "True" : "False"; In the above example you can see how we produce same output with the ternary operator without using If..Else statement. Recently in one of the project I was working with VB.NET language and I was eager to know if there is a ternary operator equivalent there or not. After searching on internet I have found two ways to do it. IF operator which works for VB.NET 2008 and higher version and IIF operator which is there since VB 6.0. So let’s check same above example with both of this operators. So let’s create a console application which has following code. Module Module1 Sub Main() Dim value As Boolean = False Dim output As String = String.Empty ''Output using if else statement If value = True Then output = "True" Else output = "False" Console.WriteLine("Output Using If Loop") Console.WriteLine(output) output = If(value = True, "True", "False") Console.WriteLine("Output using If operator") Console.WriteLine(output) output = IIf(value = True, "True", "False") Console.WriteLine("Output using IIF Operator") Console.WriteLine(output) Console.ReadKey() End If End SubEnd Module As you can see in the above code I have written all three-way to condition check using If.Else statement and If operator and IIf operator. You can see that both IIF and If operator has three parameter first parameter is the condition which you need to check and then another parameter is true part of you need to put thing which you need as output when condition is ‘true’. Same way third parameter is for the false part where you need to put things which you need as output when condition as ‘false’. Now let’s run that application and following is the output as expected. That’s it. You can see all three ways are producing same output. Hope you like it. Stay tuned for more..Till then Happy Programming.

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  • Plan Operator Tuesday round-up

    - by Rob Farley
    Eighteen posts for T-SQL Tuesday #43 this month, discussing Plan Operators. I put them together and made the following clickable plan. It’s 1000px wide, so I hope you have a monitor wide enough. Let me explain this plan for you (people’s names are the links to the articles on their blogs – the same links as in the plan above). It was clearly a SELECT statement. Wayne Sheffield (@dbawayne) wrote about that, so we start with a SELECT physical operator, leveraging the logical operator Wayne Sheffield. The SELECT operator calls the Paul White operator, discussed by Jason Brimhall (@sqlrnnr) in his post. The Paul White operator is quite remarkable, and can consume three streams of data. Let’s look at those streams. The first pulls data from a Table Scan – Boris Hristov (@borishristov)’s post – using parallel threads (Bradley Ball – @sqlballs) that pull the data eagerly through a Table Spool (Oliver Asmus – @oliverasmus). A scalar operation is also performed on it, thanks to Jeffrey Verheul (@devjef)’s Compute Scalar operator. The second stream of data applies Evil (I figured that must mean a procedural TVF, but could’ve been anything), courtesy of Jason Strate (@stratesql). It performs this Evil on the merging of parallel streams (Steve Jones – @way0utwest), which suck data out of a Switch (Paul White – @sql_kiwi). This Switch operator is consuming data from up to four lookups, thanks to Kalen Delaney (@sqlqueen), Rick Krueger (@dataogre), Mickey Stuewe (@sqlmickey) and Kathi Kellenberger (@auntkathi). Unfortunately Kathi’s name is a bit long and has been truncated, just like in real plans. The last stream performs a join of two others via a Nested Loop (Matan Yungman – @matanyungman). One pulls data from a Spool (my post – @rob_farley) populated from a Table Scan (Jon Morisi). The other applies a catchall operator (the catchall is because Tamera Clark (@tameraclark) didn’t specify any particular operator, and a catchall is what gets shown when SSMS doesn’t know what to show. Surprisingly, it’s showing the yellow one, which is about cursors. Hopefully that’s not what Tamera planned, but anyway...) to the output from an Index Seek operator (Sebastian Meine – @sqlity). Lastly, I think everyone put in 110% effort, so that’s what all the operators cost. That didn’t leave anything for me, unfortunately, but that’s okay. Also, because he decided to use the Paul White operator, Jason Brimhall gets 0%, and his 110% was given to Paul’s Switch operator post. I hope you’ve enjoyed this T-SQL Tuesday, and have learned something extra about Plan Operators. Keep your eye out for next month’s one by watching the Twitter Hashtag #tsql2sday, and why not contribute a post to the party? Big thanks to Adam Machanic as usual for starting all this. @rob_farley

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  • operator overloading of stream extraction operator in C++ help

    - by Crystal
    I'm having some trouble overloading my stream extraction operator in C++ for a hw assignment. I'm not really sure why I am getting these compile errors since I thought I was doing it right... Here is my code: Complex.h #ifndef COMPLEX_H #define COMPLEX_H class Complex { //friend ostream &operator<<(ostream &output, const Complex &complexObj) const; public: Complex(double = 0.0, double = 0.0); // constructor Complex operator+(const Complex &) const; // addition Complex operator-(const Complex &) const; // subtraction void print() const; // output private: double real; // real part double imaginary; // imaginary part }; #endif Complex.cpp #include <iostream> #include "Complex.h" using namespace std; // Constructor Complex::Complex(double realPart, double imaginaryPart) : real(realPart), imaginary(imaginaryPart) { } // addition operator Complex Complex::operator+(const Complex &operand2) const { return Complex(real + operand2.real, imaginary + operand2.imaginary); } // subtraction operator Complex Complex::operator-(const Complex &operand2) const { return Complex(real - operand2.real, imaginary - operand2.imaginary); } // Overload << operator ostream &Complex::operator<<(ostream &output, const Complex &complexObj) const { cout << '(' << complexObj.real << ", " << complexObj.imaginary << ')'; return output; // returning output allows chaining } // display a Complex object in the form: (a, b) void Complex::print() const { cout << '(' << real << ", " << imaginary << ')'; } main.cpp #include <iostream> #include "Complex.h" using namespace std; int main() { Complex x; Complex y(4.3, 8.2); Complex z(3.3, 1.1); cout << "x: "; x.print(); cout << "\ny: "; y.print(); cout << "\nz: "; z.print(); x = y + z; cout << "\n\nx = y + z: " << endl; x.print(); cout << " = "; y.print(); cout << " + "; z.print(); x = y - z; cout << "\n\nx = y - z: " << endl; x.print(); cout << " = "; y.print(); cout << " - "; z.print(); cout << endl; } Compile erros: complex.cpp(23) : error C2039: '<<' : is not a member of 'Complex' complex.h(5) : see declaration of 'Complex' complex.cpp(24) : error C2270: '<<' : modifiers not allowed on nonmember functions complex.cpp(25) : error C2248: 'Complex::real' : cannot access private member declared in class 'Complex' complex.h(13) : see declaration of 'Complex::real' complex.h(5) : see declaration of 'Complex' complex.cpp(25) : error C2248: 'Complex::imaginary' : cannot access private member declared in class 'Complex' complex.h(14) : see declaration of 'Complex::imaginary' complex.h(5) : see declaration of 'Complex' Thanks!

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  • C++ [] array operator with multiple arguments?

    - by genesys
    Can I define in C++ an array operator that takes multiple arguments? I tried it like this: const T& operator[](const int i, const int j, const int k) const{ return m_cells[k*m_resSqr+j*m_res+i]; } T& operator[](const int i, const int j, const int k){ return m_cells[k*m_resSqr+j*m_res+i]; } But I'm getting this error: error C2804 binary operator '[' has too many parameters

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  • wrong operator() overload called

    - by user313202
    okay, I am writing a matrix class and have overloaded the function call operator twice. The core of the matrix is a 2D double array. I am using the MinGW GCC compiler called from a windows console. the first overload is meant to return a double from the array (for viewing an element). the second overload is meant to return a reference to a location in the array (for changing the data in that location. double operator()(int row, int col) const ; //allows view of element double &operator()(int row, int col); //allows assignment of element I am writing a testing routine and have discovered that the "viewing" overload never gets called. for some reason the compiler "defaults" to calling the overload that returns a reference when the following printf() statement is used. fprintf(outp, "%6.2f\t", testMatD(i,j)); I understand that I'm insulting the gods by writing my own matrix class without using vectors and testing with C I/O functions. I will be punished thoroughly in the afterlife, no need to do it here. Ultimately I'd like to know what is going on here and how to fix it. I'd prefer to use the cleaner looking operator overloads rather than member functions. Any ideas? -Cal the matrix class: irrelevant code omitted class Matrix { public: double getElement(int row, int col)const; //returns the element at row,col //operator overloads double operator()(int row, int col) const ; //allows view of element double &operator()(int row, int col); //allows assignment of element private: //data members double **array; //pointer to data array }; double Matrix::getElement(int row, int col)const{ //transform indices into true coordinates (from sorted coordinates //only row needs to be transformed (user can only sort by row) row = sortedArray[row]; result = array[usrZeroRow+row][usrZeroCol+col]; return result; } //operator overloads double Matrix::operator()(int row, int col) const { //this overload is used when viewing an element return getElement(row,col); } double &Matrix::operator()(int row, int col){ //this overload is used when placing an element return array[row+usrZeroRow][col+usrZeroCol]; } The testing program: irrelevant code omitted int main(void){ FILE *outp; outp = fopen("test_output.txt", "w+"); Matrix testMatD(5,7); //construct 5x7 matrix //some initializations omitted fprintf(outp, "%6.2f\t", testMatD(i,j)); //calls the wrong overload }

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  • Operator Overloading in C

    - by Leif Andersen
    In C++, I can change the operator on a specific class by doing something like this: MyClass::operator==/*Or some other operator such as =, >, etc.*/(Const MyClass rhs) { /* Do Stuff*/; } But with there being no classes (built in by default) in C. So, how could I do operator overloading for just general functions? For example, if I remember correctly, importing stdlib.h gives you the - operator, which is just syntactic sugar for (*strcut_name).struct_element. So how can I do this in C? Thank you.

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  • Explain this C++ operator definition

    - by David Johnstone
    I have the following operator defined in a C++ class called StringProxy: operator std::string&() { return m_string; } a) What is this and how does this work? I understand the idea of operator overloading, but they normally look like X operator+(double i). b) Given an instance of StringProxy, how can I use this operator to get the m_string?

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  • C++ Operator overloading - 'recreating the Vector'

    - by Wallter
    I am currently in a collage second level programing course... We are working on operator overloading... to do this we are to rebuild the vector class... I was building the class and found that most of it is based on the [] operator. When I was trying to implement the + operator I run into a weird error that my professor has not seen before (apparently since the class switched IDE's from MinGW to VS express...) (I am using Visual Studio Express 2008 C++ edition...) Vector.h #include <string> #include <iostream> using namespace std; #ifndef _VECTOR_H #define _VECTOR_H const int DEFAULT_VECTOR_SIZE = 5; class Vector { private: int * data; int size; int comp; public: inline Vector (int Comp = 5,int Size = 0) : comp(Comp), size(Size) { if (comp > 0) { data = new int [comp]; } else { data = new int [DEFAULT_VECTOR_SIZE]; comp = DEFAULT_VECTOR_SIZE; } } int size_ () const { return size; } int comp_ () const { return comp; } bool push_back (int); bool push_front (int); void expand (); void expand (int); void clear (); const string at (int); int operator[ ](int); Vector& operator+ (Vector&); Vector& operator- (const Vector&); bool operator== (const Vector&); bool operator!= (const Vector&); ~Vector() { delete [] data; } }; ostream& operator<< (ostream&, const Vector&); #endif Vector.cpp #include <iostream> #include <string> #include "Vector.h" using namespace std; const string Vector::at(int i) { this[i]; } void Vector::expand() { expand(size); } void Vector::expand(int n ) { int * newdata = new int [comp * 2]; if (*data != NULL) { for (int i = 0; i <= (comp); i++) { newdata[i] = data[i]; } newdata -= comp; comp += n; delete [] data; *data = *newdata; } else if ( *data == NULL || comp == 0) { data = new int [DEFAULT_VECTOR_SIZE]; comp = DEFAULT_VECTOR_SIZE; size = 0; } } bool Vector::push_back(int n) { if (comp = 0) { expand(); } for (int k = 0; k != 2; k++) { if ( size != comp ){ data[size] = n; size++; return true; } else { expand(); } } return false; } void Vector::clear() { delete [] data; comp = 0; size = 0; } int Vector::operator[] (int place) { return (data[place]); } Vector& Vector::operator+ (Vector& n) { int temp_int = 0; if (size > n.size_() || size == n.size_()) { temp_int = size; } else if (size < n.size_()) { temp_int = n.size_(); } Vector newone(temp_int); int temp_2_int = 0; for ( int j = 0; j <= temp_int && j <= n.size_() && j <= size; j++) { temp_2_int = n[j] + data[j]; newone[j] = temp_2_int; } //////////////////////////////////////////////////////////// return newone; //////////////////////////////////////////////////////////// } ostream& operator<< (ostream& out, const Vector& n) { for (int i = 0; i <= n.size_(); i++) { //////////////////////////////////////////////////////////// out << n[i] << " "; //////////////////////////////////////////////////////////// } return out; } Errors: out << n[i] << " "; error C2678: binary '[' : no operator found which takes a left-hand operand of type 'const Vector' (or there is no acceptable conversion) return newone; error C2106: '=' : left operand must be l-value As stated above, I am a student going into Computer Science as my selected major I would appreciate tips, pointers, and better ways to do stuff :D

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  • Are free operator->* overloads evil?

    - by Potatoswatter
    I was perusing section 13.5 after refuting the notion that built-in operators do not participate in overload resolution, and noticed that there is no section on operator->*. It is just a generic binary operator. Its brethren, operator->, operator*, and operator[], are all required to be non-static member functions. This precludes definition of a free function overload to an operator commonly used to obtain a reference from an object. But the uncommon operator->* is left out. In particular, operator[] has many similarities. It is binary (they missed a golden opportunity to make it n-ary), and it accepts some kind of container on the left and some kind of locator on the right. Its special-rules section, 13.5.5, doesn't seem to have any actual effect except to outlaw free functions. (And that restriction even precludes support for commutativity!) So, for example, this is perfectly legal (in C++0x, remove obvious stuff to translate to C++03): #include <utility> #include <iostream> #include <type_traits> using namespace std; template< class F, class S > typename common_type< F,S >::type operator->*( pair<F,S> const &l, bool r ) { return r? l.second : l.first; } template< class T > T & operator->*( pair<T,T> &l, bool r ) { return r? l.second : l.first; } template< class T > T & operator->*( bool l, pair<T,T> &r ) { return l? r.second : r.first; } int main() { auto x = make_pair( 1, 2.3 ); cerr << x->*false << " " << x->*4 << endl; auto y = make_pair( 5, 6 ); y->*(0) = 7; y->*0->*y = 8; // evaluates to 7->*y = y.second cerr << y.first << " " << y.second << endl; } I can certainly imagine myself giving into temp[la]tation. For example, scaled indexes for vector: v->*matrix_width[2][5] = x; Did the standards committee forget to prevent this, was it considered too ugly to bother, or are there real-world use cases?

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  • Overloading *(iterator + n) and *(n + iterator) in a C++ iterator class?

    - by exscape
    (Note: I'm writing this project for learning only; comments about it being redundant are... uh, redundant. ;) I'm trying to implement a random access iterator, but I've found very little literature on the subject, so I'm going by trial and error combined with Wikpedias list of operator overload prototypes. It's worked well enough so far, but I've hit a snag. Code such as exscape::string::iterator i = string_instance.begin(); std::cout << *i << std::endl; works, and prints the first character of the string. However, *(i + 1) doesn't work, and neither does *(1 + i). My full implementation would obviously be a bit too much, but here's the gist of it: namespace exscape { class string { friend class iterator; ... public: class iterator : public std::iterator<std::random_access_iterator_tag, char> { ... char &operator*(void) { return *p; // After some bounds checking } char *operator->(void) { return p; } char &operator[](const int offset) { return *(p + offset); // After some bounds checking } iterator &operator+=(const int offset) { p += offset; return *this; } const iterator operator+(const int offset) { iterator out (*this); out += offset; return out; } }; }; } int main() { exscape::string s = "ABCDEF"; exscape::string::iterator i = s.begin(); std::cout << *(i + 2) << std::endl; } The above fails with (line 632 is, of course, the *(i + 2) line): string.cpp: In function ‘int main()’: string.cpp:632: error: no match for ‘operator*’ in ‘*exscape::string::iterator::operator+(int)(2)’ string.cpp:105: note: candidates are: char& exscape::string::iterator::operator*() *(2 + i) fails with: string.cpp: In function ‘int main()’: string.cpp:632: error: no match for ‘operator+’ in ‘2 + i’ string.cpp:434: note: candidates are: exscape::string exscape::operator+(const char*, const exscape::string&) My guess is that I need to do some more overloading, but I'm not sure what operator I'm missing.

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  • How do you override operator == when using interfaces instead of actual types?

    - by RickL
    I have some code like this: How should I implement the operator == so that it will be called when the variables are of interface IMyClass? public class MyClass : IMyClass { public static bool operator ==(MyClass a, MyClass b) { if (ReferenceEquals(a, b)) return true; if ((Object)a == null || (Object)b == null) return false; return false; } public static bool operator !=(MyClass a, MyClass b) { return !(a == b); } } class Program { static void Main(string[] args) { IMyClass m1 = new MyClass(); IMyClass m2 = new MyClass(); MyClass m3 = new MyClass(); MyClass m4 = new MyClass(); Console.WriteLine(m1 == m2); // does not go into custom == function. why not? Console.WriteLine(m3 == m4); // DOES go into custom == function } }

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  • friending istream operator with class

    - by user1388172
    hello i'm trying to overload my operator >> to my class but i ecnouter an error in eclipse. code: friend istream& operator>>(const istream& is, const RAngle& ra){ return is >> ra.x >> ra.y; } code2: friend istream& operator>>(const istream& is, const RAngle& ra) { is >> ra.x; is >> ra.y; return is } Both crash and i don't know why, please help. EDIT: ra.x & ra.y are both 2 private ints of my class; Full error: error: ..\/rightangle.h: In function 'std::istream& operator>>(std::istream&, const RAngle&)': ..\/rightangle.h:65:12: error: ambiguous overload for 'operator>>' in 'is >> ra.RAngle::x' ..\/rightangle.h:65:12: note: candidates are: c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>, std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: no known conversion for argument 1 from 'const int' to 'std::ios_base& (*)(std::ios_base&)' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}' ..\/rightangle.h:66:12: error: ambiguous overload for 'operator>>' in 'is >> ra.RAngle::y' ..\/rightangle.h:66:12: note: candidates are: c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>, std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: no known conversion for argument 1 from 'const int' to 'std::ios_base& (*)(std::ios_base&)' c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>] <near match> c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}''

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  • User defined conversion operator as argument for printf

    - by BC
    I have a class that defined a user defined operator for a TCHAR*, like so CMyClass::operator const TCHAR*() const { // returns text as const TCHAR* } I want to be able to do something like CMyClass myClass; _tprintf(_T("%s"), myClass); or even _tprintf(_T("%s"), CMyClass(value)); But when trying, printf always prints (null) instead of the value. I have also tried a normal char* operator, as well variations with const etc. It only works correctly if I explicitly call the operator or do a cast, like _tprintf(_T("%s\n"), (const TCHAR*)myClass); _tprintf(_T("%s\n"), myClass.operator const TCHAR *()); However, I don't want to cast. How can this be achieved? Note, that a possibility is to create a function that has a parameter of const TCHAR*, so that it forcible calls the operator TCHAR*, but this I also don't want to implement.

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  • How to reduce redundant code when adding new c++0x rvalue reference operator overloads

    - by Inverse
    I am adding new operator overloads to take advantage of c++0x rvalue references, and I feel like I'm producing a lot of redundant code. I have a class, tree, that holds a tree of algebraic operations on double values. Here is an example use case: tree x = 1.23; tree y = 8.19; tree z = (x + y)/67.31 - 3.15*y; ... std::cout << z; // prints "(1.23 + 8.19)/67.31 - 3.15*8.19" For each binary operation (like plus), each side can be either an lvalue tree, rvalue tree, or double. This results in 8 overloads for each binary operation: // core rvalue overloads for plus: tree operator +(const tree& a, const tree& b); tree operator +(const tree& a, tree&& b); tree operator +(tree&& a, const tree& b); tree operator +(tree&& a, tree&& b); // cast and forward cases: tree operator +(const tree& a, double b) { return a + tree(b); } tree operator +(double a, const tree& b) { return tree(a) + b; } tree operator +(tree&& a, double b) { return std::move(a) + tree(b); } tree operator +(double a, tree&& b) { return tree(a) + std::move(b); } // 8 more overloads for minus // 8 more overloads for multiply // 8 more overloads for divide // etc which also has to be repeated in a way for each binary operation (minus, multiply, divide, etc). As you can see, there are really only 4 functions I actually need to write; the other 4 can cast and forward to the core cases. Do you have any suggestions for reducing the size of this code? PS: The class is actually more complex than just a tree of doubles. Reducing copies does dramatically improve performance of my project. So, the rvalue overloads are worthwhile for me, even with the extra code. I have a suspicion that there might be a way to template away the "cast and forward" cases above, but I can't seem to think of anything.

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  • C++ stream as a parameter when overloading operator<<

    - by TheOm3ga
    I'm trying to write my own logging class and use it as a stream: logger L; L << "whatever" << std::endl; This is the code I started with: #include <iostream> using namespace std; class logger{ public: template <typename T> friend logger& operator <<(logger& log, const T& value); }; template <typename T> logger& operator <<(logger& log, T const & value) { // Here I'd output the values to a file and stdout, etc. cout << value; return log; } int main(int argc, char *argv[]) { logger L; L << "hello" << '\n' ; // This works L << "bye" << "alo" << endl; // This doesn't work return 0; } But I was getting an error when trying to compile, saying that there was no definition for operator<<: pruebaLog.cpp:31: error: no match for ‘operator<<’ in ‘operator<< [with T = char [4]](((logger&)((logger*)operator<< [with T = char [4]](((logger&)(& L)), ((const char (&)[4])"bye")))), ((const char (&)[4])"alo")) << std::endl’ So, I've been trying to overload operator<< to accept this kind of streams, but it's driving me mad. I don't know how to do it. I've been loking at, for instance, the definition of std::endl at the ostream header file and written a function with this header: logger& operator <<(logger& log, const basic_ostream<char,char_traits<char> >& (*s)(basic_ostream<char,char_traits<char> >&)) But no luck. I've tried the same using templates instead of directly using char, and also tried simply using "const ostream& os", and nothing. Another thing that bugs me is that, in the error output, the first argument for operator<< changes, sometimes it's a reference to a pointer, sometimes looks like a double reference...

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  • C++ Unary - Operator Overload Won't Compile

    - by Brian Hooper
    I am attempting to create an overloaded unary - operator but can't get the code to compile. A cut-down version of the code is as follows:- class frag { public: frag myfunc (frag oper1, frag oper2); frag myfunc2 (frag oper1, frag oper2); friend frag operator + (frag &oper1, frag &oper2); frag operator - () { frag f; f.element = -element; return f; } private: int element; }; frag myfunc (frag oper1, frag oper2) { return oper1 + -oper2; } frag myfunc2 (frag oper1, frag oper2) { return oper1 + oper2; } frag operator+ (frag &oper1, frag &oper2) { frag innerfrag; innerfrag.element = oper1.element + oper2.element; return innerfrag; } The compiler reports... /home/brian/Desktop/frag.hpp: In function ‘frag myfunc(frag, frag)’: /home/brian/Desktop/frag.hpp:41: error: no match for ‘operator+’ in ‘oper1 + oper2.frag::operator-()’ /home/brian/Desktop/frag.hpp:16: note: candidates are: frag operator+(frag&, frag&) Could anyone suggest what I need to be doing here? Thanks.

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  • operator overloading and inheritance

    - by user168715
    I was given the following code: class FibHeapNode { //... // These all have trivial implementation virtual void operator =(FibHeapNode& RHS); virtual int operator ==(FibHeapNode& RHS); virtual int operator <(FibHeapNode& RHS); }; class Event : public FibHeapNode { // These have nontrivial implementation virtual void operator=(FibHeapNode& RHS); virtual int operator==(FibHeapNode& RHS); virtual int operator<(FibHeapNode& RHS); }; class FibHeap { //... int DecreaseKey(FibHeapNode *theNode, FibHeapNode& NewKey) { FibHeapNode *theParent; // Some code if (theParent != NULL && *theNode < *theParent) { //... } //... return 1; } }; Much of FibHeap's implementation is similar: FibHeapNode pointers are dereferenced and then compared. Why does this code work? (or is it buggy?) I would think that the virtuals here would have no effect: since *theNode and *theParent aren't pointer or reference types, no dynamic dispatch occurs and FibHeapNode::operator< gets called no matter what's written in Event.

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  • Keyword Research - Four Key Criteria For Selecting "Money" Keywords

    Keyword research is absolutely essential to the success of any website because keywords are what people use to find websites and are what search engines use as the basis for their rankings. Good keyword research increases the probability that search engines will rank the pages on your website high for your target keyword; and bad keyword research (which often means no keyword research) will doom your website to the search engine cellars.

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