Programming :: Saving A PPM File - Binary Representation Of Unsigned Chars On The Harddrive

I am accessing a firewire camera using the libdc1394 library and saving the image as a PPM file, using the code below:

[Code].....

My question is whether the above code is portable. I presume it is, since the result is a binary PPM file which should be capable of being read across multiple computers with different architectures and different operating systems. But at the same time, all that the above code is doing is just saving the binary representation of unsigned chars on the harddrive, and there does not seem to be any reason why the binary representations of the unsigned chars will be identical across multiple computers.