Re: [Boost-users] How to cast form string to number safely?

From: Johan RÃ¥de (rade_at_[hidden])
Date: 2006-07-26 06:12:30

袁晓辉 wrote:
> Dear boost-users:
> 
> I am really sorry for asking shch a silly question, but I really need 
> your help!
> 
> boost::lexical_cast is a great function to do casting. If I want is to 
> cast from string to a "long long" type value, I can use the follow:
> 
> long long llVar = lexical_cast<long long>("123456789");
> 
> It is alright in this circs, but what if:
> 
> lexical_cast<long 
> long>("9999999999999999999999999999999999999999999999999999999999999999999999999999"); 
> 
> 
> This is an obvious overflow, but I have no way to handle this error, it 
> returns a wrong number without throwing an exception!
> 
> Any suggestion? Thank you very much!!!
> Kevin
> 
> 
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I tested your example with VC++ 7.1, and it throws a bad_lexical_cast.

The problem you have has nothing to do with lexical_cast.
lexical_cast uses streams to do the conversion.
It seems that you use an implementation of the C++ standard library
with poorly implemented streams.

I see two options:

1. Write your own conversion routine by hand. (Not that hard.)

2. Get a better implementation of the C++ standard library.

You can not use atoi, for its behaviour is unspecified when the 
conversion can not be carried out.

--Johan RÃ¥de