NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
The SEPDATA flag is used to mark old code relating to PR https://github.com/Unidata/netcdf-c/pull/2179. ; The old code uses incorrect code for reclaiming and copying variable length data. The new code attempts to provide general fixes for it. This flag is intentionally set to use the new code and at some point, the old code will be expunged. Looking at the non-SEPDATA code, it appears to allocate the space with the required extra space for the trailing NUL termination.So, it is unclear why this is failing. Any chance you can send/point me to the
offending file? =Dennis Heimbigner Unidata On 3/6/2023 7:41 PM, John Caron wrote:
Hello friends:The attached code shows a possible bug in the netcdf C library when reading "fixed length String" data type in HDF5 files, by not zero terminating them. The output of that program is:./testClib *** nc_inq_grp_ncid =65537 *** nc_inq_varid =0 *** nc_inq_att type=12 attlen = 1 CAPE:units[0] = 'J/kg�U' The correct answer should be CAPE:units[0] = 'J/kg' I think the problem might be in hdf5open.c, line 1904: /* Copy strings, one at a time, into their new home. Alloc space for each string. The user will later free this space with nc_free_string. */ for (i = 0; i < att->len; i++) { if (!(att->stdata[i] = malloc(fixed_size))) { free(contig_buf); BAIL(NC_ENOMEM); } strncpy(att->stdata[i], cur, fixed_size); cur += fixed_size; }This probably should be (note mallocing an extra char to be sure the string is zero terminated):for (i = 0; i < att->len; i++) { if (!(att->stdata[i] = malloc(fixed_size+1))) { free(contig_buf); BAIL(NC_ENOMEM); } strncpy(att->stdata[i], cur, fixed_size); cur += fixed_size; }IIUC, these strings are returned as char *, and theres no way to find out their length from the netcdf API. So they have to be zero terminated. Otherwise the reading code keeps reading into unallocated memory, and only stops reading when a zero byte happens to be found.From comments in the code, it would appear that this type is not used in files written with the netcdf library. If so, it only affects HDF5 files not written with netcdf library, that use "fixed length String" data types.Regards, John _______________________________________________ NOTE: All exchanges posted to Unidata maintained email lists are recorded in the Unidata inquiry tracking system and made publicly available through the web. Users who post to any of the lists we maintain are reminded to remove any personal information that they do not want to be made public. netcdfgroup mailing list netcdfgroup@xxxxxxxxxxxxxxxx For list information or to unsubscribe, visit: https://www.unidata.ucar.edu/mailing_lists/
netcdfgroup archives: