The 787 is not one piece of carbon fibre. It is very similar to the A350 design/construction with carbon fibre sections.
If you could read back what you've written before you post so that it makes sense that would help..
The A350 is using large sections of panels to create sections of the airplane like this:
THe B787 uses what they call "one-piece frames" which are somewhat larger sections than the A350's and have a full barrel to most of them. Picture explains this better:
Just imagine a bunch of those bolted together to create the fuselage.