# Attempting to build Eio code

**URL:** <https://discuss.ocaml.org/t/attempting-to-build-eio-code/13342>\
**Category:** Ecosystem\
**Tags:** dune\
**Created:** [October 31, 2023, 1:21pm UTC](https://discuss.ocaml.org/t/attempting-to-build-eio-code/13342 "2023-10-31T13:21:19Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Mohan\_Radhakrishnan](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/mohan_radhakrishnan/32/1905_2.png) [@Mohan\_Radhakrishnan](https://discuss.ocaml.org/u/Mohan_Radhakrishnan)\
**Post date:** [October 31, 2023, 1:21pm UTC](https://discuss.ocaml.org/t/attempting-to-build-eio-code/13342/1 "2023-10-31T13:21:19Z")

</div>

Hi,

Is this the way to use ‘eio’ in ‘dune’ ? `(executable (public_name vsr) (name main) (libraries eio_main))` I created a switch and installed eio.

```auto
File "bin/dune", line 4, characters 13-21:
4 | (libraries eio_main))
                 ^^^^^^^^
Error: Library "eio_main" not found.
-> required by _build/default/bin/main.exe
-> required by alias bin/all
-> required by alias default

```

Thanks.

---

<div class="post-metadata">

**Author:** ![Levi\_Roth](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/levi_roth/32/2268_2.png) [@Levi\_Roth](https://discuss.ocaml.org/u/Levi_Roth)\
**Post date:** [October 31, 2023, 1:47pm UTC](https://discuss.ocaml.org/t/attempting-to-build-eio-code/13342/2 "2023-10-31T13:47:19Z")

</div>

You’ll need to `opam install eio_main`; it isn’t included in the `eio` package.

---

<div class="post-metadata">

**Author:** ![Mohan\_Radhakrishnan](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/mohan_radhakrishnan/32/1905_2.png) [@Mohan\_Radhakrishnan](https://discuss.ocaml.org/u/Mohan_Radhakrishnan)\
**Post date:** [October 31, 2023, 2:01pm UTC](https://discuss.ocaml.org/t/attempting-to-build-eio-code/13342/3 "2023-10-31T14:01:13Z")

</div>

Yes. I ignored these errors.

```auto
-> retrieved eio_main.0.12 (cached)
-> retrieved eio_posix.0.12 (cached)
[ERROR] The compilation of eio_posix.0.12 failed at "dune build -p eio_posix -j
        15 @install".

#=== ERROR while compiling eio_posix.0.12 =====================================#
# context 2.1.5 | macos/x86_64 | ocaml-base-compiler.5.0.0 | https://opam.ocaml.org#316bd0cc
# path ~/Documents/vsr/_opam/.opam-switch/build/eio_posix.0.12
# command ~/.opam/opam-init/hooks/sandbox.sh build dune build -p eio_posix -j 15 @install
# exit-code 1
# env-file ~/.opam/log/eio_posix-1984-530377.env
# output-file ~/.opam/log/eio_posix-1984-530377.out
### output ###
# File "lib_eio_posix/dune", line 9, characters 9-24:
# 9 | (names eio_posix_stubs))
# ^^^^^^^^^^^^^^^
# (cd _build/default/lib_eio_posix && /usr/bin/cc -O2 -fno-strict-aliasing -fwrapv -pthread -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -g -I /Users/anu/Documents/vsr/_opam/lib/ocaml -I /Users/anu/Documents/vsr/_opam/lib/bigstringaf -I /Users/anu/Documents/vsr/_opam/lib/cstruct -I /Users/anu/Documents/vsr/_opam/lib/domain-local-await -I /Users/anu/Documents/vsr/_opam/lib/eio -I /Users/anu/Docu[...]
# eio_posix_stubs.c:113:7: error: implicit declaration of function 'preadv' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
# r = preadv(Int_val(v_fd), iov, n_bufs, Int63_val(v_offset));
# ^
# eio_posix_stubs.c:127:7: error: implicit declaration of function 'pwritev' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
# r = pwritev(Int_val(v_fd), iov, n_bufs, Int63_val(v_offset));
# ^
# 2 errors generated.

```