I have a fully updated and upgraded system. Running apt install libmysql++-dev returns the following:
Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: libmysql++-dev : Depends: libmysql++3v5 (= 3.2.2+pristine-2) but it is not going to be installed E: Unable to correct problems, you have held broken packages.
If I try apt install libmysql++3v5 I see the same but:
libmysql++3v5 : Depends: libmariadbclient18 (>= 5.5.36) but it is not going to be installed
And if I try apt install libmariadbclient18 I get the really interesting one:
Reading package lists... Done Building dependency tree Reading state information... Done The following packages were automatically installed and are no longer required: acl apache2-bin apg colord-data cups-pk-helper gnome-control-center-data gnome-online-accounts gnome-user-share guile-2.2-libs libapache2-mod-dnssd libaprutil1-dbd-sqlite3 libaprutil1-ldap libcolord-gtk1 libcolorhug2 libgc1c2 libgsasl7 libieee1284-3 libkyotocabinet16v5 libnss-myhostname libntlm0 librygel-core-2.6-2 librygel-db-2.6-2 librygel-renderer-2.6-2 librygel-server-2.6-2 libsane-common libsnmp-base mailutils-common mariadb-common python3-cups python3-cupshelpers python3-smbc realmd rygel system-config-printer-common system-config-printer-udev Use 'apt autoremove' to remove them. The following packages will be REMOVED: colord gnome-control-center libhpmud0 libmailutils5 libmariadb3 libsane libsnmp30 mailutils printer-driver-hpcups pureos-desktop pureos-gnome sane-utils simple-scan The following NEW packages will be installed: libmariadbclient18 0 upgraded, 1 newly installed, 13 to remove and 0 not upgraded. Need to get 785 kB of archives. After this operation, 28.6 MB disk space will be freed. Do you want to continue? [Y/n]
I think possibly libmariadbclient18 is conflicting with libmariadb3? I'm alarmed it wants to remove pureos-gnome to make this work, so I have not done it.