类含有指针数据成员的时候，将类的对象作函数参数复制传递时，出错，

#include<iostream>
#include"liuyu.hpp"
using namespace std;
int main(){
    liuyu head;

    build(head);
    display(head);
    return 0;

}

#include<iostream>
class liuyu{
public:

char *elem;
int length;
};
void build(liuyu head){
   const  int L=26;
    head.elem=new char[100];
for(int i=0;i!=L;++i){
    head.elem[i]='a'+i;}
    head.length=L;

}
void display(liuyu head){

    for(int i=0;i!=head.length;++i){
        std::cout<<(head.elem[i])<<" ";
    }


}

#include<iostream>
class liuyu{
public:

char *elem;
int length;
};
void build(liuyu &head){
   const  int L=26;
    head.elem=new char[100];
for(int i=0;i!=L;++i){
    head.elem[i]='a'+i;}
    head.length=L;

}
void display(liuyu &head){

    for(int i=0;i!=head.length;++i){
        std::cout<<(head.elem[i])<<" ";
    }


}