How Can I Customize the Delimiter for Input Streams in C ?

Customizing the Delimiter for Input Streams in C

When reading input from a stream using the extraction operator (cin), the default behavior is to read until a whitespace character is encountered. However, in certain scenarios, it may be necessary to use a custom delimiter.

Changing the Delimiter for cin

The standard library provides a way to modify the inter-word delimiter for input streams, such as cin. This can be achieved using the imbue method of std::ios_base to add a custom character type facet called ctype.

Example: Using a Colon as a Delimiter

For instance, suppose you have a file formatted like /etc/passwd, where each field is separated by a colon (:) character. To read each field separately using a custom colon-based delimiter, you can use the following code:

#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";
  }
}

In this example, a custom ctype facet named colon_is_space is created, which treats the colon character (:) and the newline character (n) as whitespace. By imbuing the input stream cin with this custom locale, the extraction operator (>>) will read each field separated by a colon.

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