Boost C++ Libraries

boost::cnv::stream accepts custom string and string-like types as input or output as long as they satisfy certain requirements.

boost::cnv::cstream cnv;
my_string        my_str("123");

cnv(std::setprecision(2))(std::fixed);

BOOST_TEST(convert<int>(my_str, cnv).value_or(0) == 123);

BOOST_TEST(convert<my_string>( 99.999, cnv).value_or("bad") == "100.00");
BOOST_TEST(convert<my_string>( 99.949, cnv).value_or("bad") ==  "99.95");
BOOST_TEST(convert<my_string>(-99.949, cnv).value_or("bad") == "-99.95");

When a string-like type is the source, then it needs to be a contiguous sequence of the corresponding character type (char or wchar_t) accessible via begin() and end().

std::stringstream is implemented entirely in terms of std::basic_streambuf which, in turn, operates on a contiguous character sequence, also called the buffer (see std::basic_streambuf for details). For efficiency reasons boost::cnv::stream uses the provided (read-only) input string as the buffer and, consequently, requires that provided input string to be a contiguous character sequence.

When a string is the target, then the described contiguous character sequence requirement does not apply. Any type that provides

MyType::MyType(char const* beg, char const* end)

constructor can be deployed in type-to-string conversions.

See The Bigger Picture chapter for the discussion of potential advantages of deploying custom strings.