有关指针复制函数的代码，为什么到了delete那儿就卡住不动了…

#include <iostream>
using namespace std;
char* fun(char* str)
{
char* str1 = new char[strlen(str+1)];
char* str2 = str1;
char* str3=str;
for(int i=0; i<strlen(str); i++)
{*str1++ = *str3++;}
*str1++ = '\0';
return str2;}
int main()
{const int MAX = 20;
char str[MAX];
char* str1;
cout << "请输入一个字符串: " << endl;
cin.getline(str, MAX, '\n');
cout << "复制字符串后: " << endl;
str1 = fun(str);
cout << str1 << endl;
delete str1;
system("pause");
return 0;
}