Thread: [DOCS] Creating variable argument user defined functions in C

Hi, 

For my project, I need to create a variable argument function which accepts
multiple strings & returns some transformed string. I've gone through the
https://www.postgresql.org/docs/9.6/static/xfunc-c.html doc..But there's no
clear documentation for variable args. 

I'able to understand we can have ArrayType as data type for same. But how to
iterate & process it??? Kindly help. 





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athinivas <athinivas@gmail.com> writes:
> For my project, I need to create a variable argument function which accepts
> multiple strings & returns some transformed string. I've gone through the
> https://www.postgresql.org/docs/9.6/static/xfunc-c.html doc..But there's no
> clear documentation for variable args. 

For ordinary array types the VARIADIC marking makes no difference so far
as the function is concerned; you just treat the last argument as a normal
array.  If you want to do VARIADIC ANY then the rules are different, since
the arguments aren't necessarily all the same type and so can't be folded
into an array.

> I'able to understand we can have ArrayType as data type for same. But how to
> iterate & process it??? Kindly help. 

There's plenty of examples in the core code.  For the normal-array
case look at anything that takes an array, e.g. json_extract_path.
For VARIADIC ANY you might look at concat() or format().
        regards, tom lane


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Thanks a lot tom lane.



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