My understanding is that the creation of an objects within a group (such
as another group or dataset) is inherently creating a hard link from
that group to the other object. So if you passed in that group or
dataset name as the "link name" argument to the H5Lget_info function it
should return H5L_TYPE_HARD, as you've stated.
If, however, you've explicitly created a soft-link to another group
using the H5Lcreate_soft function and passed _that_ name to the
H5Lget_info function, the type would be listed as H5L_TYPE_SOFT.
The following documentation helped clarify HDF5 links for me:
http://www.hdfgroup.org/HDF5/doc/UG/UG_frame09Groups.html
The following source code should clarify what I'm trying to say:
#include "hdf5.h"
#include <iostream>
using std::cout;
using std::endl;
void printLinkInfo(H5L_type_t type)
{
switch (type)
{
case H5L_TYPE_HARD: cout << "H5L_TYPE_HARD"; break;
case H5L_TYPE_SOFT: cout << "H5L_TYPE_SOFT"; break;
case H5L_TYPE_EXTERNAL: cout << "H5L_TYPE_EXTERNAL"; break;
case H5L_TYPE_ERROR: cout << "H5L_TYPE_ERROR"; break;
}
}
int main()
{
const char* main_file = "hard_vs_soft.h5";
hid_t file = H5Fcreate(main_file, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
hid_t g1 = H5Gcreate(file, "/G1", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
hid_t g2 = H5Gcreate( g1, "G2", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
hid_t g3 = H5Gcreate( g1, "G3", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
hid_t g4 = H5Gcreate(file, "/G4", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
hid_t status = H5Lcreate_soft("/G1/G3", g4, "G5_soft", H5P_DEFAULT,
H5P_DEFAULT);
{
// test one hard and one soft link to make sure...
H5L_info_t info;
status = H5Lget_info(g1, "G2", &info, H5P_DEFAULT);
cout << "/G1/G2 is "; printLinkInfo(info.type); cout << endl;
status = H5Lget_info(g4, "G5_soft", &info, H5P_DEFAULT);
cout << "/G4/G5_soft is "; printLinkInfo(info.type); cout << endl;
}
status = H5Gclose(g4);
status = H5Gclose(g3);
status = H5Gclose(g2);
status = H5Gclose(g1);
status = H5Fclose(file);
return 0;
}
Richard.
Jens Thoms Toerring wrote:
Hi Quincy,
On Tue, Oct 12, 2010 at 02:28:41PM -0500, Quincey Koziol wrote:
Hmm, sorry, I missed that you wanted to check for a soft link. You
need to use H5Lget_info() for that.
Sorry for bothering you again: is it the expected behaviour of
H5Lget_info() that it reports the type as H5L_TYPE_HARD in the
H5L_info_t structure if what is passed as the 'link_name' argu-
ment is actually just a group? I was expecting to get back a
negative return value but that only seems to happen if a group
or (soft) link with the specified name does not exist. May I
conclude that a group is basically a hard link?
Thanks and best regards, Jens
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