Thread: [HACKERS] How to refer to resource files from UDFs written in C

On 06/09/2017 08:56 AM, Supun Nakandala wrote:
> Hi hackers,
>
> I am trying to extend PostgreSQL by adding UDT and UDF for a custom use
> case and I am using C language extensions to do that.
>
> However, I have a requirement of reading a text file from one of the C
> functions. The compiled *.so files are placed in the "pg_config
> --pkglibdir" directory and tried copying my text files there but it didn't
> work. I found that, when these shared libs are loaded they are run from a
> different working directory. In this case, what is the best way to refer to
> my text files from the C code other than giving the absolute path which can
> change from system to system.

All backend processes run with the data directory as the current 
directory. So you can put the files into the data directory, probably 
best to have a subdirectory there to avoid confusing them with 
PostgreSQL's own files. Or you could have a config option, to set an 
absolute path.

- Heikki

Supun Nakandala <supun.nakandala@gmail.com> writes:
> However, I have a requirement of reading a text file from one of the C
> functions. The compiled *.so files are placed in the "pg_config
> --pkglibdir" directory and tried copying my text files there but it didn't
> work. I found that, when these shared libs are loaded they are run from a
> different working directory. In this case, what is the best way to refer to
> my text files from the C code other than giving the absolute path which can
> change from system to system.

You probably want to use get_share_path, or one of its sibling functions
in src/port/path.c.  Then your files go with the PG installation tree,
whereever it is.  There are different functions that are appropriate for
different types of files.
        regards, tom lane