[julia-users] Very strange results ccall-ing a c function which modifies a char **

[Zenna Tavares]

I am attempting to wrap the Parma Polyhedron Primitive Library.

It has a function 'ppl_version' which modifies a set of strings, 
represented as a char **.  An example function which calls 'ppl_version' is 
as follows: 

get_ppl_version() {
  const char* p;
  (void) ppl_version(&p);
  return p;
}


My Julia attempt is as follows:

function get_ppl_version()
  versionnum = Array{Uint8}[Array(UInt8, 20) for i = 1:4]
  res = ccall((:ppl_version, "libppl_c"), Int, (Ptr{Ptr{Uint8}},), 
versionnum)
  bytestring(convert(Ptr{Uint8}, versionnum[1]))
end

However, I get gobbledygook back

@show get_ppl_version() 
=>$(Expr(:call, :ppl_version)) => "Xٮ\n"

Actually the result is non-deterministic, evaluating it a few times gives 
very strange results, e.g. ""set_bigfloat_roundin",  "isppl_initialzied", 
ec. which seems to be random mix of my julia soure-code and c code from the 
api itself.  I'm not sure how that is even possible.  What am I doing wrong?

Thanks