Thanks for the reply,
I figured out casting from v.get<int> to C++'s unsigned long doesn't make
any data loss, as you said in your mail
I'd like to point out the lack of this information on the documentation on
the website !
In the future, I hope this could change, and be able to use directly C++
types in the get<T> template function, or at least something less strict
like
- short (0 to 255); int (0 to 65K); long (0 to 4M); and long 64 for greate
values
- bool's, and something else for other specific types.
IMO, this could give some noob-friendly startup for the library !
Thanks again,
nico
2013/3/5 Pawel Aleksander Fedorynski <[email protected]>
>
>
> Hello Nico,
>
> Right now SOCI (or at least the MySQL backend) is very strict about the
> types when using the row interface. This is often inconvenient and we
> should probably change it. But for now the rules are:
>
> - All integer types smaller than INT are promoted to int, regardless
> whether the original type was signed or unsigned. So, e.g., if you select
> a value of type TINYINT UNSIGNED, you should retrieve it from the rowset
> using v.get<int>("id").
>
> - INT is retrieved as int: v.get<int>("id")
>
> - INT UNSIGNED is retrieved as (signed) long long: v.get<long long>("id"),
> although this will work too: v.get<unsigned>("id").
>
> - BIGINT is retrieved as long long.
>
> - BIGINT UNSIGNED is retrieved as unsigned long long.
>
> If you don't know the type that was selected form the database, you can
> use v.get_properties("id").get_data_type() to find out. It will be
> dt_unsigned_long_long for BIGINT UNSIGNED, dt_long_long for BIGINT and INT
> UNSIGNED, and dt_integer for all the smaller integral types.
>
> Unless I'm mistaken this problem only pertains to the row interface
> (dynamic binding), when you use static binding, i.e., into(n) this should
> be more forgiving with respect to types.
>
> Thanks,
>
> Aleksander
>
> On Tue, Mar 5, 2013 at 6:21 AM, Nicolas Deroche <[email protected]>wrote:
>
>>
>> Hello,
>>
>> I just started using SOCI, and I have one quick question about casting
>>
>> Consider this structure:
>> struct A
>> { unsigned long one; unsigned int two; unsigned short three; }
>>
>> In MySQL, the fields are defined like:
>> one : INT unsigned
>> two: SMALLINT unsigned
>> three: TINYINT unsigned
>>
>> How am I supposed to cast using the static templated function from_base
>> the SQL values into my structure?
>> static void from_base(values const & v, indicator /* ind */, A& s)
>> {
>> s.one = v.get<unsigned long>("id"); /// Throws std::bad_cast()
>> }
>>
>> Thanks,
>>
>> nico
>>
>>
>>
>>
>>
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>
>
>
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