Re: Wrapping a C library.
- Posted by mattlewis (admin) Jan 17, 2012
- 1868 views
I'm getting a type check error when I use the gnuplot_plot_xy() function.
Looking at the include file, I see that the parameters x and y are atoms, however, writing the euphoria equivalent of the example given in the documentation:
...
I took it that x and y being arrays here, then in the corresponding Eu code x and y would be sequences.
I think this is something to do with the fact that x and y are not actually arrays, but pointers to arrays. Unfortunately my knowledge of C is nil so I'm just confused...
Yes, a C array is really just a pointer. To use it, you'll need to allocate some memory and poke and peek the data (there should be an easier way coming in 4.1). So, something like this:
include std/convert.e include std/machine.e sequence x = repeat( 0, 50 ) atom x_array = allocate( length( x ) * 8 ) -- doubles are 8 bytes each -- write your sequence into an array: for i = 1 to length( x ) do poke( x_array + (i-1) * 8, atom_to_float64( x[i] ) ) end for -- read the array in memory into a sequence: for i = 1 to length( x ) do x[i] = float64_to_atom( peek( { x_array + (i-1) * 8, 8 } ) end for
Ideally, you'd probably put that sort of thing into functions/procedures, and use them as needed.
Matt
