Default parameters for templates in C++: Like function default arguments, templates can also have default arguments. For example, in the following program, the second parameter U has the default value as char. 1 #include<iostream> 2 using namespace…
template <typename T> class A { ); }; template<typename T> ) { /* */ } 对于类似上文代码,VS编译器会报 “an out-of-line definition of a member of a class template cannot have default arguments”错误. 其原因在于:带有默认参数值的模板类成员不能在类外进行定义,修改方式有两种. 第一种在类内进行定义: template <…
Default arguments are a helpful feature, but there is one situation where they can be surprisingly unhelpful. Using a mutable type (like a list or dictionary) as a default argument and then modifying that argument can lead to strange results. It's us…
Predict the output of following C++ program. 1 #include <iostream> 2 using namespace std; 3 4 class Base 5 { 6 public: 7 virtual void fun ( int x = 0 ) 8 { 9 cout << "Base::fun(), x = " << x << endl; 10 } 11 }; 12 13 clas…
Python’s handling of default parameter values is one of a few things that tends to trip up most new Python programmers (but usually only once). What causes the confusion is the behaviour you get when you use a “mutable” object as a default value; tha…
Default Function Parameters.md Default Function Parameters function getSum(a,b){ a = (a !== undefined) ? a : 1 ; b = (b !== undefined) ? b : 41; console.log(a+b); } getSum(); getSum(1,2); getSum (10); getSum(null, 6); In ES5,if the argument is not sp…
