2 Datasets

This chapter presents the interfaces of the PnetCDF functions that deal with a netCDF dataset or the whole PnetCDF library.

A netCDF dataset (file) that has not yet been opened can only be referred to by its dataset name. Once a netCDF dataset is opened, it is referred to by a netCDF ID, which is a small non-negative integer returned when you create or open the dataset. A netCDF ID is much like a file descriptor in C or a logical unit number in FORTRAN. In any single program, the netCDF IDs of distinct open netCDF datasets are distinct. A single netCDF dataset may be opened multiple times and will then have multiple distinct netCDF IDs; however at most one of the open instances of a single netCDF dataset should permit writing. When an open netCDF dataset is closed, the ID is no longer associated with a netCDF dataset.

Functions that deal with the PnetCDF library include:

• Get version of library.
• Get error message corresponding to a returned error code.

The operations supported on a netCDF dataset as a single object are:

• Create, given dataset name and whether to overwrite or not.
• Open for access, given dataset name and read or write intent.
• Put into define mode, to add dimensions, variables, or attributes.
• Take out of define mode, checking consistency of additions.
• Close, writing to disk if required.
• Inquire about the number of dimensions, number of variables, number of global attributes, and ID of the unlimited dimension, if any.
• Synchronize to disk to make sure it is current.
• Set and unset nofill mode for optimized sequential writes.
• After a summary of conventions used in describing the PnetCDF interfaces, the rest of this chapter presents a detailed description of the interfaces for these operations.