Is there a limit on the name of an HDF4 dataset?

No. HDF has always allowed any length to be specified for a name, when creating an SDS, Vdata, or Vgroup. However, prior to HDF 4.2r2, the behavior was undefined for names that were greater than 64 characters, which caused problems for tools reading the data. Either characters were concatenated to the name or, in the case of the hdp tool, a crash occurred due to accessing undefined memory.

As of HDF 4.2r2, released in 2007, this issue was fixed and a name with any length could be retrieved. The SDgetnamelen, Vgetnamelen*, and Vgetclassnamelen* APIs were introduced for retrieving the length of a name.

* Vgetnamelen and Vgetclassnamelen were added to the source code in HDF 4.2r2, but were inadvertently left out of the documentation until HDF 4.2.5, and are therefore listed in the Release Notes for HDF 4.2.5.