I'm curious about this, too, so I read up on the internet. The best answer, on Stack Overflow, basically says that you can set the file buffer to your own pointer, using setvbuf, but the file operations are then free to do whatever they want with the contents of that memory. One of the answerers suggests that the poster should complain to the original library owner to add additional functions that take arrays. So, it seems you would do best to revise your library.