HP 3000 Manuals HP 3000 Manuals
Variables
Table 5-4. Variables
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| SPL | HP C/XL Equivalent |
| | |
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| Syntax of a variable in an expression: | Syntax of a variable in an expression: |
| | |
| 1. simple-id | 1. simple-id |
| | |
| 2. array/ptr-id | 2. array/ptr-id "["0"]" OR *array/ptr-id |
| | |
| 3. array/ptr-id ( index ) | 3. array/ptr-id "[" index "]" |
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| 4. @identifier | 4. &identifier |
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| 5. @array/ptr-id | 5. &array/ptr-id "[" 0 "]" OR array/ptr-id |
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| 6. @array/ptr-id ( index ) | 6. &array/ptr-id "[" index "]" |
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| 7. TOS | 7. No equivalent. |
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| 8. ABSOLUTE ( index ) | 8. No equivalent. |
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| Syntax of a variable on the left of an | Syntax of a variable on the left of an |
| assignment operator (:=): | assignment operator (=): |
| | |
| a. simple-id | a. simple-id |
| | |
| b. array/ptr-id | b. array/ptr-id "[" 0" ]" OR *array/ptr-id |
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| c. array/ptr-id ( index ) | c. array/ptr-id "[" index "]" |
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| d. @ptr-id | d. ptr-id |
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| e. TOS | e. No equivalent. |
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| f. ABSOLUTE ( index ) | f. No equivalent. |
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| The address operator, "@", specifies the | The address operator is "&". |
| location of a variable, rather than its | |
| contents. | An unsubscripted array-id or pointer-id is |
| | an address rather than cell zero; either |
| An unsubscripted pointer-id or array-id is | add the subscript or use the "*" operator. |
| assumed to be subscripted by zero. | |
| | |
| See "Addresses (@) and Pointers" below. | |
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| The assignment operator is ":=". | The assignment operator is "=". |
| | |
| | Note: The HP C/XL assignment operator, |
| | "=", is the SPL equality operator. |
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| Indexes are enclosed in parentheses, "( )". | Indexes are enclosed in brackets, "[ ]". |
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SPL allows assignment to the array-id of an indirect array since it is
really a pointer. HP C/XL does not permit assignments to any array-id.
You may simulate the process by using a pointer to array cell zero. (See
"ARRAY Declaration".)
The reserved word TOS and the ABSOLUTE function cannot be translated (see
below). Their operations must be recoded entirely.
TOS
Table 5-5. TOS
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| SPL | HP C/XL Equivalent |
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| TOS | No equivalent. |
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| Refers to the top of the hardware stack. | You could write routines to emulate the |
| | hardware stack, but a better solution is to |
| | recode SPL programs to eliminate stack |
| | references. |
| | |
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Addresses (@) and Pointers
Table 5-6. Addresses and Pointers
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| SPL | HP C/XL Equivalent |
| | |
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| The address operator, "@", before a simple | The address operator, "&", before any |
| variable-id yields the address of the | variable-id yields the address of the |
| variable instead of its contents. If "@" | variable. Before a subscripted pointer-id |
| precedes an array or pointer reference, it | or array-id, it yields the address of the |
| yields the address of cell zero or of the | referenced location. |
| indexed location if indexed. | |
| | The dereference operator, "*", before a |
| If "@" precedes an unsubscripted pointer-id | pointer expression yields the value of the |
| or indirect array-id on the left side of | referenced location. An array-id can be |
| the assignment operator, ":=", the | used as a pointer in an expression. |
| right-side expression is stored as the new | |
| address value in the identifier. | An unsubscripted pointer-id or array-id |
| | yields the address in the identifier. |
| This leads to a potentially confusing | |
| feature of SPL: | |
| | |
| @ARRAYNAME := @NEWARRAY; | |
| | |
| This assigns the address of NEWARRAY(0) to | |
| array variable ARRAYNAME. Consequently, | |
| ARRAYNAME(0) and NEWARRAY(0) both refer to | |
| the same location. | |
| | |
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| All SPL addresses are 16-bit quantities | All HP C/XL addresses are 32-bit |
| that may be stored in integer and logical | quantities. |
| variables. It is preferable to store | |
| addresses in pointer variables, but the | In many cases, the SPL logical arrays may |
| lack of pointer "arrays" in SPL has led to | be converted to HP C/XL pointer arrays |
| some applications that store addresses in | without difficulty. |
| logical arrays. | |
| | |
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Table 5-7 compares various uses of the SPL "@" operator and the
equivalent HP C/XL assignment.
Table 5-7. Assignments Using Pointers and Simple Variables
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| SPL | HP C/XL | Operation |
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| POINTER P1,P2; | unsigned int *P1,*P2; | Declarations |
| | | |
| LOGICAL V3; | unsigned int V3; | |
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| P1 := P2 | *P1 = *P2 | Object of P2 stored in |
| | | object of P1 |
| | | |
| P1 := @P2 | *P1 = P2 | Address in P2 stored in |
| | | object of P1 |
| | | |
| @P1 := @P2 | P1 = P2 | Address in P2 stored in P1 |
| | | |
| @P1 := P2 | P1 = *P2 | Object of P2 stored in P1 |
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| P1 := V3 | *P1 = V3 | Value of V3 stored in object |
| | | of P1 |
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| P1 := @V3 | *P1 = &V3 | Address of V3 stored in |
| | | object of P1 |
| | | |
| @P1 := @V3 | P1 = &V3 | Address of V3 stored in P1 |
| | | |
| @P1 := V3 | P1 = V3 | Value of V3 stored in P1 |
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| V3 := P2 | V3 = *P2 | Object of P2 stored in V3 |
| | | |
| V3 := @P2 | V3 = P2 | Address in P2 stored in V3 |
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Absolute Addresses
Table 5-8. Absolute Addresses
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| SPL | HP C/XL Equivalent |
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| absolute-address: | No equivalent. |
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| ABSOLUTE ( index ) | |
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The use of absolute addresses in MPE V is entirely system-dependent, and
only permitted in privileged mode. They must be recoded in HP C/XL.