关于c++中读写string类型变量进出文件read()和write()的问题?

Question

# include<iostream># include<string># include<fstream>using namespace std;void f1(){	ofstream out("尝试.dat", ios::binary | ios::out);	string str;	str = "ABC";	int len = str.size();	cout<<len<<endl;	out.write((char *)(& len), sizeof(int));	out.write(str.c_str(), len);	out.close();}void f2(){	ifstream in("尝试.dat", ios::binary | ios::in);	int length;	char * p;	in.read((char *)(& length), sizeof(int));	p = new char[length + 1];	in.read(p, length);	p[length] = '\0';	cout<<p<<endl;	string st;	st = p;	cout<<st;		in.close();}int main(){	f1();	f2();		return 0;}

  // 为什么write()和read()的第二操作数可以是字符数,不应该是字节数是吗?