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The current set of primitive types supported by the netCDF interface are:
byte
character
byte; intended for
representing text strings as arrays of ASCII characters.
short
long
float
double
Except for the added byte and the lack of
unsigned types, netCDF supports the same primitive data types as C. The
names for the primitive data types are reserved words in CDL, so the
names of variables, dimensions, and attributes must not be type names.
Whether byte, short, or long data is interpreted as signed or unsigned
is not part of the netCDF interface; since no netCDF operations depend
on the sign or order of variable data, you are free to interpret a byte,
for example, as holding values between 0 and 255 or between -128 and
127. For convenience, short and long constants are interpreted as
signed in the CDL notation. See section Attribute Conventions for more
information on representing signedness of values.
These types were chosen because they are familiar to C and FORTRAN programmers, they have well-defined external representations independent of any particular computers (using XDR), and they are sufficient for providing a reasonably wide range of trade-offs between data precision and number of bits required for each datum.
Additional primitive types may be added in the future, but only in a way
that is compatible with existing programs and files. For example,
hyperlong for 64-bit integers will eventually be needed, along
with a new type for multibyte characters, but these can both be added
without affecting existing netCDF files or applications, and with
only minor changes required for generic applications that will support
them.
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