How Can I Customize Input Stream Delimiters in C ?

Customizing Input Stream Delimiters in C

Input streams, such as the standard input stream std::cin, use whitespace characters as delimiters by default. However, what if you need to use an alternative character as the delimiter?

Unfortunately, the C standard library does not provide a straightforward way to change the delimiter for std::cin. However, there is a workaround using the std::ios_base::imbue function to add a custom ctype facet.

The code below demonstrates how to change the delimiter for std::cin to the colon character, effectively reading delimited words in the style of /etc/passwd.

#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() {
  std::cin.imbue(std::locale(std::cin.getloc(), new colon_is_space));

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

In this code, the colon_is_space class is defined as a custom ctype facet that identifies the colon (':' ) and newline ('n' ) characters as space characters. By imbuing this facet into std::cin, we effectively extend the recognition of whitespace characters to include the colon.

As a result, when you use the std::cin >> operator, it will read words delimited by colons. This allows you to easily parse data files that follow a colon-separated format.

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