c++ - 创建新map对象问题

Question

在《c++ primer》练习11.7中，当指定的家庭不存在时有一段代码如下：

families[family]=vector<string>();

这段代码最后一个括号作用是嘛啊- - 是哪一部分的知识呢？？

Answer 1

vector<string> represents a type
vector<string>() represents a (temporary) variable created by this type (equivalent to directly calling the constructor, but here a parameterless constructor is called, thus creating an anonymous temporary variable)

Answer 2

Call the default constructor of vector<string> to generate a vector object.
For example, there is a class A. Yes, A a = A(); is possible. This object is not new, so it is on the stack.