operator-keyword | 易学教程

<?= operator C++ greater less question mark equals sign

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问题 I saw <?= and >?= used in a code: http://community.topcoder.com/stat?c=problem_solution&rm=151152&rd=5854&pm=2923&cr=310333 I tried to compile without the includes to test if it's standard, but it didn't work. I then added the includes, but it still gives the same error: question-mark.cpp:15:5: error: expected primary-expression before ‘?’ token question-mark.cpp:15:6: error: expected primary-expression before ‘=’ token question-mark.cpp:15:9: error: expected ‘:’ before ‘;’ token question

isSet() or operator void*() or explicit opertor bool() or something else?

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问题 What is the state of the art about functions to check whether a value is set or not ? For example, the below iterator parses cells. Some cells contain a value, other cells are empty. What is the most convenient way? struct iterator { //usage: bool isset() const // if (it.isset()) bool isSet() const // if (it.isSet()) bool empty() const // if (it.empty()) bool is_set() const // if (it.is_set()) bool is_valid() const // if (it.is_valid()) operator void*() const; // if (it) explicit operator

Why does 1.add(2) not work out? [duplicate]

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问题 This question already exists : Closed 7 years ago . Possible Duplicate: accessing a python int literals methods In Python, everything is an object . But then again, why doesn't the following snippet work? 1.__add__(2) However, this does work: n = 1 n.__add__(2) What is the difference between n and 1 ? Isn't it a design failure that it doesn't work? For instance, it does work with string literals as well. "one".__add__("two") For comparison, it works well on other purely object oriented

@ error suppression operator and set_error_handler

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问题 I am following good programming practices and I am logging the PHP errors to file instead of displaying it to user. I use set_error_handler() for that. Now the problem. For example, I have somewhere: @file_exists('/some/file/that/is/outside/openbasedir.txt'); But despite the error suppression operator, the error message logs. I don't want that. I want suppressed errors not to pass to my error handler. 回答1: The @ operator temporarily sets error_reporting to 0, so you can test the value of

C++ Operator Overloading [ ] for lvalue and rvalue

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问题 I made a class Array which holds an integer array. From the main function, I'm trying to get an element of the array in Array using [ ] as we do for arrays declared in main. I overloaded the operator [ ] as in the following code; the first function returns an lvalue and the second an rvalue (Constructors and other member functions are not shown.) #include <iostream> using namespace std; class Array { public: int& operator[] (const int index) { return a[index]; } int operator[] (const int

Bitwise Logic in C

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I have some familiarity with bitwise operations, but this function just went over my head. void binary_print(unsigned int value) { unsigned int mask = 0xff000000; // Start with a mask for the highest byte. unsigned int shift = 256*256*256; // Start with a shift for the highest byte. unsigned int byte, byte_iterator, bit_iterator; for (byte_iterator=0; byte_iterator < 4; byte_iterator++) { byte = (value & mask) / shift; // Isolate each byte. printf(" "); for (bit_iterator=0; bit_iterator < 8; bit_iterator++) { // Print the byte's bits. if (byte & 0x80) // If the highest bit in the byte isn't 0,

Overload * operator in python (or emulate it)

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问题 I want to overload the * operator in python. In C++, you can overload the dereference operator, so that you can create a class with a custom way to respond to *alpha . Part of this question is that I don't know exactly, and I mean EXACTLY, what the * operator (unpacking operator as I call it) does. So how can I overload it, or emulate the overloading of it. Eventually I want to be able to do: *alpha with a custom response and return value. EDIT: I found the solution thanks to Joe Kington's

operator << overload

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//using namespace std; using std::ifstream; using std::ofstream; using std::cout; class Dog { friend ostream& operator<< (ostream&, const Dog&); public: char* name; char* breed; char* gender; Dog(); ~Dog(); }; im trying to overload the << operator. I'm also trying to practice good coding. But my code wont compile unless i uncomment the using namespace std. i keep getting this error and i dont know. im using g++ compiler. Dog.h:20: error: ISO C++ forbids declaration of ‘ostream’ with no type Dog.h:20: error: ‘ostream’ is neither function nor member function; cannot be declared friend. if i add

Operator [] in two dimensional vector

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I want to create an operator [] in the case of two dimensional vector. After searching, I have found that it's impossible to pass two arguments. How I can obtain the value of m_matrix[i][j] in the main? relevant code: class MyMatrix { public: // Methods MyMatrix(); ~MyMatrix(); int operator[] (int n); private: // Attributes int m_n; int m_m; std:: vector <std:: vector <int> > m_matrix; }; int MyMatrix::operator[](int n, int m) // in the cpp { if (n>=0 && m>=0 && n<=m_n && m<=m_m) { return m_matrix[n-1][m-1]; } else { cout<<"******************"<<endl; cout<<"No valid index"<<endl; cout<<"******

Iterate through a sequence of operators

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Is it possible/Is there a way to iterate through a sequence of operators as in the following example? a, b = 5, 7 for op in (+, -, *, /): print(a, str(op), b, a op b) One possible use case is the test of the implementation of various operators on some abstract data type where these operators are overloaded. You can use the operator module. for op in [('+', operator.add), ('-', operator.sub), ('*', operator.mul), ('/', operator.div)]: print("{} {} {} = {}".format(a, op[0], b, op[1](a, b))) You can create your own operations, then iterate through them. def add(a, b): return a + b def sub(a, b):