lexical_cast to multimember object fails

[Darko Veberic <darko.veberic@…>]

According to the documentation, the only relevant requirement for the lexical_cast<target>(source) is that the target is input-streamable. Having a simple class

struct Foo {
  int fA;
  int fB;
};

with input operator

istream&
operator>>(istream& is, Foo& f)
{
  return is >> f.fA >> f.fB;
}

should satisfy all the requirements. Nevertheless, the code

const string s = "137 13";
const Foo f = lexical_cast<Foo>(s);

compiles without any warnings (g++ 4.4.1) but eventually throws a bad_lexical_cast exception. Of course, using a non-optimized non-boost version of the lexical cast

template<typename T, typename U>
T
LexicalCast(const U& u)
{
  stringstream ss;
  ss << u;
  T t;
  if (ss >> t)
    return t;
  else
    throw bad_lexical_cast();
}

works fine for the class in the example above. Are there additional requirements on the target type that are not mentioned in the documentation or is this a really severe bug?

[Steven Watanabe]

You need to use std::ws between the two integers, because Boost.LexicalCast turns off skipping white space by default.

[Darko Veberic <darko.veberic@…>]

thanks, this solved the problem. the input operator thus has to be defined as

istream&
operator>>(istream& is, Foo& f)
{
  return is >> f.fA >> ws >> f.fB;
}

(what a n00b mistake...)