Get the channel descriptor handle of a particular index
#include <xdfio.h>
struct xdfch* xdf_get_channel(const struct xdf* xdf,
unsigned int index);
xdf_get_channel() gets the channel descriptor of the channel stored at index index in the XDF file referenced by the handle xdf.
xdf_get_channel() returns the handle to requested channel descriptor in case of success, NULL otherwise.
EINVAL
xdf is NULL or index is bigger than the number of channel.