Yyou might want to take a look at using facets to add the extra options needed to control input/output through << and >> http://stdcxx.apache.org/doc/stdlibug/25-1.html

From: JDlugosz@TradeStation.com To: boost-users@lists.boost.org Date: Wed, 23 Jun 2010 12:30:23 -0400 Subject: [Boost-users] Providing a string-to-X feature

Suppose I wanted to expose a "parse from string" feature for my data type. For discussion, I'll suppose it's a date/time type since everyone knows that and it illustrates the worst problems.

What is the current thought on the "best practices" way to expose this? Maybe I'll start with a stream operator>>, and make sure it works with lexical_cast<X>(string). But, where do I add the extra options that tells it what to allow or assume when parsing? Dates for example might have different formats and it can recognize any legal format, but you can tell it to ignore some since that clashes with other input data. It contains spaces and trailing components are optional, so it doesn't know when to stop until it runs into something that doesn't fit.

In some sense, that ought to be a constructor. But it should take any kind of string-like thing or stream, and the declaration might clash with other more normal constructors, so a purpose-named "take from human-readable form" is better.

An earlier discussion touched on whether to use lexical_cast or a to_string function. This is the other direction, but might have similar issues. Only from_string doesn't seem to be as omni-present as an expectation.

Any suggestions?

--John

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