Can C 's `cin` Use Custom Delimiters?

Custom Delimiters for C 's cin

Problem:

When using cin after redirecting it to a file stream (via cin.rdbuf(inF.rdbug())), it reads until reaching a white space character. Is it possible to use an alternative delimiter?

Answer:

Yes, it is possible to change the inter-word delimiter for cin (or any other std::istream) using std::ios_base::imbue and a custom ctype facet.

A custom facet that treats colons (:) and newlines as whitespace characters can be used to read files like /etc/passwd, where fields are separated by colons.

#include <locale>
#include <iostream>

struct colon_is_space : std::ctype<char> {
  colon_is_space() : std::ctype<char>(get_table()) {}
  static mask const* get_table()
  {
    static mask rc[table_size];
    rc[':'] = std::ctype_base::space;
    rc['\n'] = std::ctype_base::space;
    return &amp;rc[0];
  }
};

int main() {
  using std::string;
  using std::cin;
  using std::locale;

  cin.imbue(locale(cin.getloc(), new colon_is_space));

  string word;
  while (cin >> word) {
    std::cout << word << "\n";
  }
}

By applying this custom facet to the input stream, cin will now interpret colons and newlines as word delimiters, allowing for the separation of fields in files like /etc/passwd.

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