C++ io read/write is mostly done using the following two classes

ofstream: Stream class to write into files

istream: Stream class to read from file

ioReadWrite.cpp shows how you can write and read some custom data using binary format. The reason to use binary format is to scale it up or do the read/write efficiently.

ReadSourceDataByIndex shows how one can read just one particular object data from the file, rather than loading everything into memory.