The pit of std::string::find return value

Look at a bug first:

 string str = "csdn";unsigned int i = str.find("-");if (i < 0){cout << "Not Found";}else{cout << "Found";}

The bug is that unsigned int cannot be < 0, so this code must go to else.We all know the common correct spelling:

 string str = "csdn";int i = str.find("-");if (i < 0){cout << "Not Found";}else{cout << "Found";}

But in fact the return value of string::find is really unsigned

 string str = "csdn";auto i = str.find("-");cout << typeid(i).name() << endl;

Here, when string::find does not exist, it actually returns string::npos, so the standard writing should be:

 string str = "csdn";if (str.find("-") == string::npos){cout << "Not Found\n";}else{cout << "Found\n";}