Re: How to convert a double value to a numeric datum type in pgsql?

[Pavel Stehule <pavel.stehule@xxxxxxxxx>]

2014-02-24 8:42 GMT+01:00 Felix.徐 <ygnhzeus@xxxxxxxxx>:

Thanks , I find another function called OidInputFunctionCall which can automatically generate a datum from a string for any data type, but seems it is not recommended in the comments.

it is little bit different - and it needs a second conversion - double -> string

Regards

Pavel

 

2014-02-24 15:32 GMT+08:00 Pavel Stehule <pavel.stehule@xxxxxxxxx>:

hello

you have to look to postgresql/src/backend/utils/adt/numeric.c functions -

then you can call float8_numeric

Numeric result = DatumGetNumeric(DirectFunctionCall1(float8_numeric, Float8GetDatum(dx));

regards

Pavel

2014-02-24 7:45 GMT+01:00 Felix.徐 <ygnhzeus@xxxxxxxxx>:

Hi all,

I'm talking about the source code of pgsql and I want to know how the typing system works in pgsql.

A few functions can help us do the type conversion, for example:

Int32GetDatum -- convert a integer to a datum

Float8GetDatum -- convert double to a datum

cstring_to_text -- convert a string to a text

...

but there are a lot of types in pgsql,how to choose the corresponding function? or is there a more automatic way to do the type conversion(raw chars to a datum, suppose I have the corresponding Form_pg_type instance)?

I ask this question because I don't know how to convert a double value to a numeric datum(the field's type is numeric(10,2)), pg_type shows that numeric's typlen is -1 whose length is variable thus Float8GetDatum is not working..