SPL to HP C/XL Migration Guide (30231-90001)

4-10
In the second example, the DB area is equivalenced in a union with a
structure that places cell zero of reference array ABC_DEF at location
DB[10]. The pointer ABC is used to reference the array cells of ABC_REF,
thus overcoming the undefined subscript range problem presented by the
unbounded direct array in SPL. ABC_REF is a direct array.
POINTER Declaration
Table 4-4. POINTER Declaration
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| SPL | HP C/XL Equivalent |
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| pointer-declaration :| pointer-declaration :|
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| [GLOBAL] [ type ] POINTER ptr-defn [,...] ;| [static] [ type ] ptr-defn [,...] ; |
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| ptr-defn :| ptr-defn :|
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| 1a. ptr-id | 1a. * ptr-id |
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| 1b. ptr-id := @ ref-id | 1b. * ptr-id =& ref-id |
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| 1c. ptr-id := @ ref-id ( index ) | 1c. * ptr-id =& ref-id "[" index "]" |
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| 2a. ptr-id = ref-id ||
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| 2b. ptr-id = ref-id sign offset ||
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| 3a. ptr-id = register ||
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| 3b. ptr-id = register sign offset ||
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|4. ptr-id = offset ||
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| Default type: LOGICAL | Default type: int (= long int) |
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| Pointers are 16-bit values containing | Pointers are 32-bit values containing |
| DB-relative addresses. | standard MPE XL addresses. |
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| | Overlays of pointers and other data types |
| | must be recoded. |
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| Pointers may be initialized to addresses. | Same as SPL. |
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| INTEGER POINTER P := @IVAR; | short int *P = &IVAR; |
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| declares a pointer P, as a pointer to type | declares a pointer P, as a pointer to type |
| INTEGER data, and initializes it to the | short int data, and initializes it to the |
| address of the integer variable IVAR. | address of the short integer variable IVAR. |
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| Pointers may contain either byte addresses | Pointers always contain byte addresses, |
| or 16-bit word addresses, depending on the | regardless of the type of data being |
| data type. The rule is that BYTE pointers | pointed to. |
| contain byte addresses, and all other types | |
| contain word addresses. | Unlike SPL, HP C/XL automatically scales |
| | the operands used in pointer arithmetic, so |
| Consequently, many SPL programs contain | adding one--"*( ptr +1)"--to a type char |
| runtime code to "convert" between byte and | pointer increments it by one, but adding |