cin getline输入问题

大家好，我想问一个问题。就是
#include <iostream>
#include <cstring>

using namespace std;

struct datas{
    string name;
    double diameter;
    double weight;
};

int main()
{
    datas *pn = new datas;

    cout<<"Enter the diameter of the pizza:\n";
    cin>>pn->diameter;
   
    cout <<"Enter the name:\n";
    getline(cin,pn->name);

    cout <<"Enter the weight of the pizza:\n";
    cin>>pn->weight;

    cout <<pn->name<<"\n"<<pn->diameter<<"\n"<<pn->weight<<endl;
    delete pn;
    return 0;
}
这个程序为什么不能在输入diameter后不等待输入name而直接就出现Enter the name:Enter the weight of the pizza麻烦哪位高手帮帮我！！先谢谢了！