c++ - 调用运算符和默认构造函数

Question

关于符号()，它不是用在类名后面作用是调用默认构造函数，用在类的对象后边作用是函数调用运算符嘛。
但是在书里边有这样一行代码sort(svec.begin(),svec.end(),greater<string>());为嘛说它是调用给定的greater函数对象呢？

Answer 1

means that greater<string>() returns a function object constructed by calling the default constructor

Answer 2

greater is a class template, which overloads the operator() internally. In addition, function objects are defined as follows function objects are instances of a class with member operator() defined. this member function allows the object to be used with the same syntax as a function call. Therefore, the object of greater is a function object. greater<string>(), calls the default constructor to generate a temporary object.