# How to use functions in xtcio.h from third-party program with gromacs 2021.1

**URL:** <https://gromacs.bioexcel.eu/t/how-to-use-functions-in-xtcio-h-from-third-party-program-with-gromacs-2021-1/2456>\
**Category:** User discussions\
**Created:** [July 6, 2021, 2:02am UTC](https://gromacs.bioexcel.eu/t/how-to-use-functions-in-xtcio-h-from-third-party-program-with-gromacs-2021-1/2456 "2021-07-06T02:02:39Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![tnagai](https://avatars.discourse-cdn.com/v4/letter/t/ee59a6/32.png) [@tnagai](https://gromacs.bioexcel.eu/u/tnagai)\
**Post date:** [July 6, 2021, 2:02am UTC](https://gromacs.bioexcel.eu/t/how-to-use-functions-in-xtcio-h-from-third-party-program-with-gromacs-2021-1/2456/1 "2021-07-06T02:02:39Z")

</div>

GROMACS version: 2021.1  
GROMACS modification: No

I used gromacs 2019.2 and analyzed the trajectories by my own programs.  
These programs call functions in xtcio.h to directly read xtc files.  
In particular, I included GMXroot/include/gromacs/fileio/xtcio.h and linked the programs by -lgromacs.

Recently, I have tried to move to a newer version of gromacs,  
and I realized that the xtcio.h file is there anymore.

Is there any way to use to the xtcio.h file and link my program with gromacs2021.1?

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<div class="post-metadata">

**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\
**Post date:** [July 7, 2021, 12:19pm UTC](https://gromacs.bioexcel.eu/t/how-to-use-functions-in-xtcio-h-from-third-party-program-with-gromacs-2021-1/2456/2 "2021-07-07T12:19:35Z")

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The file is there in my gmx 2021 tree.

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<div class="post-metadata">

**Author:** ![tnagai](https://avatars.discourse-cdn.com/v4/letter/t/ee59a6/32.png) [@tnagai](https://gromacs.bioexcel.eu/u/tnagai)\
**Post date:** [July 8, 2021, 1:45am UTC](https://gromacs.bioexcel.eu/t/how-to-use-functions-in-xtcio-h-from-third-party-program-with-gromacs-2021-1/2456/3 "2021-07-08T01:45:22Z")

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I installed gromacs2021.2 again but I could not find the file under the installation directory,  
but I found it in source tree.

Here is my installation script.

```auto
~/programs/cmake-3.21.0-rc2-linux-x86_64/bin/cmake .. \
 -DGMX_BUILD_OWN_FFTW=ON -DGMX_DOUBLE=OFF \
 -DCMAKE_INSTALL_PREFIX=~/programs/gromacs-2021.2/ \
 -DGMX_X11=ON -DGMX_GPU=OFF -DREGRESSIONTEST_DOWNLOAD=ON\
 -DGMX_MPI=OFF
make -j 10
make install -j 10

```

I checked files by

```auto
ls -p ~/programs/gromacs-2021.2/include/gromacs/

```

then I find only four directories,

```auto
math/ mdrun/ restraint/ utility/

```

On the other hand, I can find the following files under the installation directory of gromacs2019.2 (`~/programs/gromacs-2019.2/include/gromacs/`):

```auto
analysisdata/ fileio/ mdtypes/ restraint/ trajectoryanalysis/
analysisdata.h gmxana/ options/ selection/ trajectoryanalysis.h
commandline/ gpu_utils/ options.h selection.h utility/
commandline.h linearalgebra/ pbcutil/ timing/ utility.h
compat/ math/ random/ topology/ version.h
fft/ mdlib/ random.h trajectory/

```

And I used the fileio/xtcio.h there previously.

Anyway, I found it in the source file, gromacs-2021.2/src/gromacs/fileio/, probably as hess meant.  
Also, I was able to dynamically link my programs to the gromacs so files.

I would appreciate if someone could tell me whether the elimination from the installation directory was on purpose. (I just might have overlooked some comment in release notes, though.)

Many thanks.