boost format

Boost.Format provides a class called boost::format, wich is defined in boost/format.hpp Similar to std::printf(), a string containing special characters to control formatting is passed to the constructor of boost::format. The data that replaces these special characters in the output is linked via the operator operator%

#include <boost/format.hpp>
#include <iostream>

int main() {
  std::cout << boost::format(%1%.%2%.%3%) % 12 % 5 % 2014 << std::endl;
  std::cout << boost::format(%2%/%1%/%3%) % 12 % 5 % 2014 << std::endl;
  return 0;
}

The boost format string uses numbers placed between two percent signs as placeholders for the actual data, which will be linked in using operator%.

The output is:

12.5.2014

5/12/2014

Boost.Format is boty type safe and extensible. Objects of any type can be used with Boost.Format as long as the operator operator<< is overloaded for std::ostream.

#include <boost/format.hpp>
#include <string>
#include <iostream>

struct animal {
  std::string name;
  int legs;
};

std::ostream& operator<<(std::ostream& os, const animal& a) {
  return os << a.name << "," << a.legs;
}

int main() {
  animal a{"cat", 4};
  std::cout << boost::format("%1%") %ａ << std::endl;
  return 0;
}

Output: cat, 4

uses boost::format to write an object of the user-defined type animal to standard output. This is possible because the stream operator is overloaded for animal.

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