有如下的程序：#include <cstring> #include<iostream>using namespace std; class MyString{public:MyString(const char *s);~MyString() {delete []data;} protected:unsigned len;char * data;};MyString::MyString(const char *s){len = strlen(s);data = new char[len+1];strcpy(data,s);}int main(){MyString a("C++ Programming");MyString b(a);return 0;}在运行上面的程序时出错，出错的原因是（ ）。