text: #include <iostream>
  #include <string>
  using namespace std;
  int main()
  {
  	string str;
  	if(str.empty())
  		cout << "str is NULL" << ",length" << str.length() << endl;
  	else
  		cout << "str is not NULL" << endl;
  	str = str.append("abcdefg");
  	cout << "str is" << str << ",size=" << str.size() << endl;
  	const char* p = str.c_str();
  	cout << "p =" << p << endl;
  	cout << "find:" << str.find("de", 0) << endl;  //查找成功
  	cout << "fine:" << str.find("de", 4) << endl;  //查找失败
  	string str1 = str.insert(4, "123");
  	cout << str1 << endl;
  	return 0;
  }
  
  	
  		
  