sizeof 可变参数的模版特化 C++ templa

1 sizeof 测量函数返回值大小的时候，是不执行函数的

2 可变参数列表可以没有一个参数，只是不能用参数了（这句不知到对不对）

3 可变参数列表再模版实例化过程中比较弱；

#include <iostream>using namespace std;long long fun1(...){cout << "in fun1 class" << endl;return 3l;}class MyClass{public:typedef int x;};template <typename T>char tmpfun1(typename T::x);template <typename T>long long tmpfun1(...);#define has_member_of_X(T) (sizeof(tmpfun1<T>(0)) == 1)int main(){fun1(1);fun1("adfdf");cout << "sizeof(fun1) = " << sizeof(fun1(2)) << endl;if(has_member_of_X(int))cout << "int has type member x" << endl;elsecout << "int has not member x" << endl;if(has_member_of_X(MyClass))cout << "MyClass has type member x"<< endl;elsecout << "MyClass has not type member x" << endl;int i;cin >> i;}