An Introduction & Guide to JALV2
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2.3. Constants

2.3.1. Unnamed Constants

An unnamed numeric constant has the type UNIVERSAL, which is a 32-bit signed value. When a value of type UNIVERSAL is used in an operation, it is converted to the type of the other operand.

Numeric constants have the following formats:

12 -- decimal
0x12 -- hexadecimal
0b01 -- binary
0q01 -- octal
"a" -- ASCII

An ASCII constant evaluates to the first character except when used to initialize a constant or variable array in which case each character is used as one entry.

For example: 


            VAR BYTE ch = "123"    ' ch is set to '1'
            VAR BYTE str[] = "123" ' str[0] is set to '1'
                                   ' str[1] is set to '2'
                                   ' str[2] is set to '3'

An ASCII constant allows the C language escaping rules as follows:

Table 2-2. ASCII Constant Escaping

Sequence Value
"\0qqq" octal constant
"\a" bell
"\b" backspace
"\f" formfeed
"\n" line feed
"\r" carriage return
"\t" horizontal tab
"\v" vertical tab
"\xdd" hexidecimal constant
"\\" A single '\'

constants other than ASCII constants may also contain any number of underscores ("_") which are ignored, but are useful for grouping. For example: 0b0000_1111

2.3.2. Named Constants

The complete format for defining a named constant is: 


          CONST [type[*cexpr]] identifier [ '[' [ cexpr ] ']' ]
            '=' { cexpr | '{' cexpr1[',' cexpr2...]'}' | '"'...'"'}
            [ ',' identifier2...]

CONST

CONST denotes the beginning of a constant definition clause.

type[*cexpr]

Defines the type of the constant. If none is given, the constant becomes universal type which is 32 bit signed.

'[' [ cexpr ] ']'

Defines a constant array (see array variable types). A constant array will not take any space unless it is indexed at least once with a non-constant subscript. On the PIC, constant arrays consume *code* space, not *data* space, and are limited to 255 elements.

If cexpr is ommitted, the size of the array will be determined by the number of initializers used.

'=' cexpr

For non-array constants this assigns the value to the constant

'=' '{' cexpr[',' cexpr2...] '}'

For arrays of constants this assigns the value to each element. There must be the same number of cexprs as there are elements defined.

'=' '"' ... '"'

For an array of constants, this assigns each ASCII value between '"' and '"' to one element of the constant array. Unlike C, there is no terminating NUL.

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