Re: [Boost-users] [lexical_cast] Input/ouput to stringstream ok, but not with lexical_cast

On Wed, 15 Mar 2006, Delfin Rojas wrote:

The problem with your example was that after you read the first double there was a blank space in the input so you could not read the second double. Something like this will do:

istream& operator >> ( istream& in , vec& v ) { for ( int i = 0 ; i < vec::size ; ++ i ) if ((in >> v.data[ i ]) && !in.eof()) in.get(); return in ; }

As far as I know, when using operator>> on numbers (or any types supported by the standard library), preceding spaces are skept, unless explicitly told not to. Mm, after peeking a little more deeply in , I noticed that they do deactivate white space skipping... Argh, my damn old habits... Well, I'll have to use ">> ws" everywhere in operator>>'s now, or temporarily reenable it.

I ran into another little problem while debugging your example so I thought I would mention it. Although the documentation does not explicitly say so you kind of make sense that lexical_cast expects the destination object's operator>> to use the complete output produced by the source object's operator<<. In other words:

stream << source stream >> target !!! stream.eof() must be true at this point

So if you try (like I did) lexical_cast<vec>("1 2 3") with vec.size = 2 it will fail.

I know that. Thanks for your help! -- François Duranleau LIGUM, Université de Montréal "The real source of wealth is correct ideas: workable ideas: that is, negative entropy -- Information." - Robert Anton Wilson, _Prometheus Rising_, 1983