如何使用重定向的标准输入（即cin）读取文件（注意：不使用ifstream）

Question

Plus: I redirected standard input by editing the command argumennts in property pages in VS2013. I'm doing a small project and it requires I read a file without using the ifstream cause it's said: The only libraries you may use for this assignment are iostream, iomanip, and string.

Answer 1

You want to redirect cin to a file and for that you need to set the stream buffer associated with cin using

ios::rdbuf()

Take a look here

and a couple more on SO here and here

Answer 2

You can use "freopen" functionn. Example:

freopen("input.txt","r",stdin).

That means you read a file "input.txt" and save it's contents to "stdin". Now, you can use "cin".

Answer 3

When file is redirected to stdin (standard input), you should read from std::cin (instance of std::istream ) which is wrapper around stdin. std::basic_ifstream is a subclass of std::basic_istream , so most reading functions are available in both of them and you should familiar with them. Which means that you can use:

• std::getline to read file line by line:

   std::string s; while(std::getline(std::cin, s)) { std::cout << s << std::endl; } 

• operator >> to read fields delimited by space character:

   while(std::cin) { std::string s; std::cin >> s; std::cout << s << std::endl; } 

Check out full list of its operators and functions here: http://en.cppreference.com/w/cpp/io/basic_istream