On Tuesday, 2 February 2016 at 22:56:28 UTC, jmh530 wrote:
I'm working on generating a binding to a C library. I've got
the .h file converted and can call some parts of the library
with no errors. However, I have reached a stumbling block in a
critical part.
The library requires passing function pointers to various
functions in the library. When I try to run these functions, I
get an Access Violation error. I enabled additional DMD
warnings, which helped pinpoint the issue.
My D code calls a C function. One of the parameters to the C
function is a function pointer to a D function. This D function
(below) is one that I copied from the C library's tutorial. I
only slightly changed the signature. This function is
eventually called in other functions in the C library.
double myfunc(uint n, const double* x, double* grad, void*
my_func_data)
{
if (grad)
{
grad[0] = 0.0;
grad[1] = 0.5 / sqrt(x[1]);
}
return sqrt(x[1]);
}
The line (though likely the next will too) that causes a
problem is
grad[0] = 0.0;
Thus, as it is an Access Violation, I'm guessing the issue is
with accessing elements of arrays in the D function from the C
function. I don't know. When I try to call the D function in D,
it works, but I have to refer to x and grad as x.ptr and
grad.ptr.
I'm not sure how to go about fixing this...
Is grad allocated in the D code? If so, it could have been
collected because the GC lost track of its use when passing to
and from the C code. Or is grad owned by the C code? If so,
either there is a bug in the library or it's misused, because its
memory has been freed/has never been allocated/has gone out of
scope.
