Chapter 6. Boost.LexicalCast

Boost.LexicalCast provides a cast operator, boost::lexical_cast, that can convert numbers from strings to numeric types like int or double and vice versa. boost::lexical_cast is an alternative to functions like std::stoi(), std::stod(), and std::to_string(), which were added to the standard library in C++11.

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

int main()
{
  std::string s = boost::lexical_cast<std::string>(123);
  std::cout << s << '\n';
  double d = boost::lexical_cast<double>(s);
  std::cout << d << '\n';
}

The cast operator boost::lexical_cast can convert numbers of different types. Example 6.1 first converts the integer 123 to a string, then converts the string to a floating point number. To use boost::lexical_cast, include the header file boost/lexical_cast.hpp.

boost::lexical_cast uses streams internally to perform the conversion. Therefore, only types with overloaded operator<< and operator>> can be converted. However, boost::lexical_cast can be optimized for certain types to implement a more efficient conversion.

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

int main()
{
  try
  {
    int i = boost::lexical_cast<int>("abc");
    std::cout << i << '\n';
  }
  catch (const boost::bad_lexical_cast &e)
  {
    std::cerr << e.what() << '\n';
  }
}

If a conversion fails, an exception of type boost::bad_lexical_cast, which is derived from std::bad_cast, is thrown. Example 6.2 throws an exception because the string “abc” cannot be converted to a number of type int.