Re: [Cppcms-users] Cppdb: How to fetch a column of unknown type at compile time?

[Artyom <art...@ya...>]

>
>From: Klaim <mj...@gm...>
>To: cpp...@li...
>Sent: Tue, January 4, 2011 12:18:59 PM
>Subject: Re: [Cppcms-users] Cppdb: How to fetch a column of unknown type at 
>compile time?
>
>Hi,
>reading this example
>
>
> try {
>>       int x = r.get<int>(v);
>>     }
>>     catch(cppdb::bad_value_cast const &e) {
>>       // ok it can't be integer
>>     }
>
>I'm thinking : could it be possible to provide a way to make it return a 
>specific value instead of throwing when the conversion can't be done?
>I'm not sure that would be useful in this case but it have been when using 
>boost::property_tree for example.
>Something like 
>
>
> int x = r.get<int>( v ,  -1 ); // return -1 if something gone wrong
> 
>Alllowing the two syntaxes help avoiding unnecessary try/catch when you just 
>want an obviously wrong result instead of a potential exception you'll have to 
>remember to catch to stop crashing.
>

Generally you can do following:

   int x = -1;
   r.fetch(v,x);


HOWEVER this works only when the value is NULL value, in case of impossible
type conversion bad_value_cast would be thrown.

If you don't want the bad_value_cast being thrown when you don't know the type,
just fetch the value as string and manipulate over it.

Artyom