HP 3000 Manuals HP 3000 Manuals
Using Subroutines When there are a set of operations that you perform repeatedly from different parts of your program, you should code them once as a subroutine. Then, when you want to execute the subroutine, you enter a Calculation Specification to perform it. RPG has two kinds of subroutines. Internal subroutines are part of an RPG program. External subroutines are independent load modules that are written in Business BASIC, C, Pascal, SPL or COBOL. Internal Subroutines To perform an internal subroutine, enter an EXSR Calculation Specification operation. Place the subroutine, itself, after the last Calculation Specification in the program. The BEGSR operation marks the beginning of an internal subroutine and always has a tag associated with it. You use this tag to execute the subroutine. To end an internal subroutine, follow the last line in the subroutine with an ENDSR operation. Figure 5-14 shows how internal subroutines are coded. In this example, the subroutine is named, INQRY.Figure 5-14. Using an Internal Subroutine Comments 1 This line performs the internal subroutine INQRY when a user presses function key F3. (Conditioning the EXSR operation is optional.) Columns 28-32 contain EXSR to execute an internal subroutine. Columns 33-38 contain the name of the internal subroutine, INQRY. 2 This line begins the INQRY internal subroutine. Columns 7-8 contain SR to indicate that this is a subroutine line (SR is optional on this and subsequent subroutine lines). Columns 18-23 contain the name of the internal subroutine INQRY. Columns 28-32 contain BEGSR to mark the beginning of the internal subroutine. 3 This line transfers control to the end of the internal subroutine. You cannot use GOTO operations to transfer control out of the subroutine. 4 This line ends the internal subroutine. Columns 18-23 contain the tag, INQRY9. (A tag is used in this particular example, though it is optional.) Columns 28-32 contain ENDSR to end the internal subroutine. External Subroutines External subroutines are separate procedures; you do not code them as part of an RPG program. For example, you can code an external subroutine in Business BASIC. You then compile it, and place it in an executable library using HP Link Editor/XL. To execute the external subroutine from an RPG program, enter an EXIT Calculation Specification operation. The HP RPG Reference Manual contains information on how to create external subroutines in COBOL and other languages. There are two ways to pass information to external subroutines. The first method uses the Calculation Specification operation, RLABL, to name the fields, arrays, tables or indicators that you want to pass. The second method uses the Calculation Specification operation, PARM, to name the fields, arrays and tables to pass. PARM is more limited than RLABL because you cannot pass indicators. Also, PARM values are available only to the subroutine executed with the PARM operation(s). The next two sections explain how to use external subroutines and how to pass parameters to them using RLABL and PARM. Using RLABL. RLABL passes field names, tables, arrays and indicators to external subroutines. Values passed by RLABL are available to all external subroutines in the program. Figure 5-15 shows a portion of a C procedure that is used as an external subroutine. Just the statements defining the data that is passed to the procedure (the field, PNAME, and the indicator, IN20) are shown. Figure 5-16 shows how to execute this C procedure from an RPG program. _____________________________________ | | | VOID SUB01() | | { | | EXTERN CHAR PNAME[]; | | EXTERN INT IN20; | | . | | . | | . | | } | | | _____________________________________ Figure 5-15. An External Subroutine written in C Figure 5-16 lists the Specifications that execute the external subroutine, SUB01, shown in the previous figure. The RPG program passes indicator 20 (IN20) and the field (PNAME) to the subroutine.Figure 5-16. Using RLABL to Pass Information to an External Subroutine Comments 1 This line makes indicator 20 available to an external subroutine. Columns 43-48 specifies that indicator 20 is passed to the external subroutine. (Prefix indicator names by IN.) 2 This line makes the field, PNAME, available to an external subroutine. 3 This line executes the external subroutine, SUB01. Using PARM. PARM passes field names, tables and arrays to external subroutines. PARM does not pass indicators. Also, you must code PARM operations for each external subroutine called. PARM values are not globally available to other external subroutines in a program. (See Figure 8-4 for a complete program that uses external subroutines and PARM.) RPG variables used with PARM are passed to external subroutines as byte values by reference. The corresponding external subroutine variables must be declared accordingly. (All RPG numeric fields have packed decimal formats.) Figure 5-17 shows part of a C procedure that is executed as an external subroutine. Only the statements defining the data that is passed to the procedure are shown. Figure 5-18 shows how this C procedure is executed from an RPG program. _____________________________________ | | | VOID SUB01 (PNAME, STATUS) | | CHAR *PNAME; | | CHAR *STATUS; | | { | | . | | . | | . | | } | | | _____________________________________ Figure 5-17. An External Subroutine Written in C Figure 5-18 shows how to execute the C procedure shown in Figure 5-16. The RPG program passes two fields to the C procedure, PNAME and STATUS. The C procedure may alter the value in STATUS, indicating that an error occurred in the external subroutine.Figure 5-18. Using PARM to Pass Information to an External Subroutine Comments 1 This line moves a program name, RPT10, to the first parameter field, PNAME. This field is passed to the external subroutine. 2 This line sets the field, STATUS, to zeros. This field is passed to the external subroutine. The subroutine returns an error code in this field. 3 This line executes the external subroutine, SUB01. SUB01 is the C procedure shown in Figure 5-17. 4 This line passes the field, PNAME, to the external subroutine. (You enter PARM operations immediately after the EXIT operation.) 5 This line passes the field, STATUS, to the external subroutine. 6 This line tests the value in STATUS. The external subroutine can modify this field.
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