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This section explains the CDL notation for netCDF constants.
Attributes are initialized in the variables section of a CDL description
by providing a list of constants that determines the attribute's type
and length. (In the C and FORTRAN procedural interfaces to the netCDF
library, the type and length of an attribute must be explicitly provided
when it is defined.) Since neither C nor FORTRAN provide suitable
standard syntax to distinguish between constants of type byte and
char, short and long, or float and
double (except that FORTRAN provides the latter), CDL defines a
syntax for constant values that allows it to determine the netCDF type
of any constant.
The syntax for CDL constants is similar to C syntax, except that type
suffixes are appended to shorts and floats to distinguish
them from longs and doubles.
A byte constant is represented by a single character or multiple
character escape sequence enclosed in single quotes. For example:
'a' // ASCII a '\0' // a zero byte '\n' // ASCII newline character '\33' // ASCII escape character (33 octal) '\x2b' // ASCII plus (2b hex) '\377' // 377 octal = 255 decimal, a non-ASCII byte
Character constants are enclosed in double quotes. A character array may be represented as a string enclosed in double quotes. Multiple strings are concatenated into a single array of characters, permitting long character arrays to appear on multiple lines. To support multiple variable-length string values, a conventional delimiter such as `,' may be used, but interpretation of any such convention for a string delimiter must be implemented in software above the netCDF library layer. The usual escape conventions for C strings are honored. For example:
"a" // ASCII `a' "Two\nlines\n" // a 10-character string with two embedded newlines "a bell:\007" // a string containing an ASCII bell "ab","cde" // the same as "abcde"
The form of a short constant is an integer constant with an
`s' or `S' appended. If a short constant begins with
`0', it is interpreted as octal. When it begins with
0x, it is interpreted as a hexadecimal constant. For example:
2s // a short 2 0123s // octal 0x7ffs // hexadecimal
The form of a long constant is an ordinary integer constant,
although it is acceptable to append an optional `l' or `L'.
If a long constant begins with `0', it is interpreted as
octal. When it begins with 0x, it is interpreted as a
hexadecimal constant. Examples of valid long constants include:
-2 1234567890L 0123 // octal 0x7ff // hexadecimal
The float type is appropriate for representing
data with about seven significant digits of precision.
The form of a float constant is the same as a C floating-point constant
with an `f' or `F' appended. A decimal point is required in a CDL
float to distinguish it from an integer. For example,
the following are all acceptable float constants:
-2.0f 3.14159265358979f // will be truncated to less precision 1.f .1f
The double type is appropriate for representing floating-point
data with about 16 significant digits of precision. The form of a
double constant is the same as a C floating-point constant. An
optional `d' or `D' may be appended. A decimal point is
required in a CDL double to distinguish it from an
integer. For example, the following are all acceptable double
constants:
-2.0 3.141592653589793 1.0e-20 1.d
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