OSLib File Basics

Hi all

I’m working on code to read files from file system into memory, and write memory to files. There are a fair few options in osfile_ and I was wondering if anyone had any examples of this I could look at which might be faster than trying to work out the best option via trial/error.

Thanks

Dave

I’ve just done something like this. I used OS_File 10 to save a block of memory to file, and OS_File 16 to load it. These two take a single parameter for the file, so it’s a full file path and name. No messing with path lists or wildcards.

Hope that helps.

Yes thank you. This led me to the relevant chapter in my PRM as well :)

I’m still not clear about how memory allocation works. My untested working assumption is that I have to allocate enough memory to hold the contents of the file and provide the address of this buffer on read. Which I assume means I have to stat the file to work out how big it is.

Which I assume means I have to stat the file to work out how big it is.

That will be OS_File 17, which returns the length in R4. I’d allow a small margin to that.

Yes, OS_File 16 and 17 work together. Here is how to convert a pathname to its contents, as a string, with Lua:

path_to_string = function (pathname)
local sys, dim, $, block in riscos
local r0, r1, r2, r3, r4 = sys ("OS_File", 17, pathname)
if r0 ~= 1 then 
  return nil, pathname .. " not a file"
end -- if
local buffer = dim (r4)
sys ("OS_File", 16, pathname, buffer, 0)
local s = $ (buffer, r4)
block[buffer] = nil -- buffer can now be garbage-collected
return s
end -- function