Development requirements below Ubuntu 20.04

OCAP requires GCC 9+ (to support c++17) & cmake 3.16+

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update
sudo apt install -y gcc-9 g++-9 libstdc++6
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 9
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 9

wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | sudo apt-key add -
sudo apt-add-repository 'deb https://apt.kitware.com/ubuntu/ bionic main'
sudo apt update
sudo apt install cmake

also you will need zlib and curl

sudo apt install zlib1g-dev
sudo apt install libcurl4-openssl-dev

alternative way to configure alternative gcc-9

update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 \
                    15 \
                    --slave   /usr/bin/cc cc /usr/bin/gcc-9 \
                    --slave   /usr/bin/c++ c++ /usr/bin/g++-9 \
                    --slave   /usr/bin/g++ g++ /usr/bin/g++-9 \
                    --slave   /usr/bin/gcov gcov /usr/bin/gcov-9 \
                    --slave   /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-9 \
                    --slave   /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-9 \
                    --slave   /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-9 \
                    --slave   /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-9 \
                    --slave   /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-9

and switch gcc version later via

update-alternatives --config gcc