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The explicitly provided converter as in
int i = boost::convert<int>("123", converter).value();
      provides considerable flexibility, configurability and efficiency. However,
      in certain contexts that might be not that important or even counter-productive
      if, for example, an application relies on certain consistent behavior associated
      with one particular converter type and configuration. To accommodate such a
      scenario Boost.Convert introduces the concept of the
      default converter implemented as boost::cnv::by_default.
    
| ![[Important]](../../../../../doc/src/images/important.png) | Important | 
|---|---|
| There is no default converter set by default. | 
Consequently, without additional configuration steps the following call will fail to compile:
int i = boost::convert<int>("123").value(); // No converter provided
      However, after boost::cnv::by_default
      is defined simply as:
    
struct boost::cnv::by_default : boost::cnv::cstream {};
or potentially configured with additional formatting:
struct boost::cnv::by_default : boost::cnv::cstream { by_default() { (*this)(std::uppercase)(std::hex); } };
      the code compiles and deploys boost::cnv::cstream when boost::convert() is called without an explicitly supplied
      converter:
    
// No explicit converter provided. boost::cnv::by_default is used. int i = boost::convert<int>("F").value_or(-1); std::string s = boost::convert<std::string>(255).value_or("bad"); // 'i' and 's' are converted using boost::cnv::cstream // with std::uppercase and std::hex formatting applied. BOOST_TEST(i == 15); // 15(10) = F(16) BOOST_TEST(s == "FF"); // 255(10) = FF(16)
      The trade-off for the convenience is the rigid converter configuration (which
      in certain contexts might be the desired behavior) and a potential performance
      impact. When a converter is not provided explicitly, the default converter
      is created, potentially configured, deployed and destroyed for every boost::convert() call. Consequently, if efficiency of this
      particular component is important, then the implementation of boost::cnv::by_default
      will need to take that into account and to make sure those operations are cheap.