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I don't think Irrlicht's file API will actually commit the contents to disk until the pointer is dropped. I recomend staying away from a binary file format or something that can be confusing, try something like TinyXML or Irrlicht's built in XML parser.
But the question really was how does Irrlicht work with binary files, I would like to know that too.
The same way every application deals with binary files, by recreating the data. To write a string to a binary file, one method is to get the length of the string and then save those characters like {3pfo} in the binary file. f32 is just a float, you can write it right into the file, u32 is an unsigned int, again, can be written right into the file. When you read the binary data back in, you need to know what elements are stored in what order to read it correctly.