**Note: on systems with no `sudo` access, one can replace `./configure` with `./configure prefix=${PWD}/_install` in order to execute `make install/uninstall` commands without `sudo` privileges.**
The primary TREXIO API is composed of the following functions:
-`trexio_open`
-`trexio_write_[group]_[variable]`
-`trexio_read_[group]_[variable]`
-`trexio_has_[group]_[variable]`
-`trexio_close`
where `[group]` and `[variable]` substitutions correspond to the contents of the `trex.json` configuration file (for more details, see the corresponding [documentation](https://trex-coe.github.io/trexio/trex.html) page).
For example, consider the `coord` variable (array), which belongs to the `nucleus` group. The TREXIO user can write or read it using `trexio_write_nucleus_coord` or `trexio_read_nucleus_coord` functions, respectively.
Note: the `[variable]` names have to be unique only within the corresponding parent `[group]`.
There is no naming conflict when, for example, `num` variable exists both in the `nucleus` group (i.e. the number of nuclei) and in the `mo` group (i.e. the number of molecular orbitals).
These quantities can be accessed using the corresponding `trexio_[has|read|write]_nucleus_num` and `trexio_[has|read|write]_mo_num`, respectively.
Note: The code should be compliant with the C99 [CERT C coding
standard](https://resources.sei.cmu.edu/downloads/secure-coding/assets/sei-cert-c-coding-standard-2016-v01.pdf). This can be checked with the `cppcheck` tool.
