If you are interested to learn about the file handling verb
Cobol subroutine is a program that can be compiled independently but cannot be executed independently. There are two types of subroutines: internal subroutines like Perform statements and external subroutines like CALL verb.
Call Verb
Call verb is used to transfer the control from one program to another program. The program that contains the CALL verb is the Calling Program and the program being called is known as the Called Program. Calling program execution will halt until the called program finishes the execution. Exit Program statement is used in the Called program to transfer the control back.
What is difference between static and dynamic call in COBOL?
Precisely, a Static call is faster and takes less CPU time since the load module sits with the main program’s load module. However, the Dynamic call is slower and takes more CPU time since the load module is separately stored and takes extra time to place with the main module
How do you write a subprogram in COBOL?
In COBOL, there are three ways of transferring control to a subprogram. In the first form, the called subprogram is specified as an alphanumeric literal. In the second form, name refers to the COBOL data area with length equal to that required for the name of the subprogram
Called Program Constraints
Following are the called program requirements −
- Linkage section must be defined in the called program. It consists of data elements passed in the program. The data items should not have Value clause. PIC clause must be compatible with the variables passed through the calling program.
- Procedure division using has a list of variables passed from the calling program and the order must be same as mentioned in the Call verb.
- Exit program statement is used in the called program to transfer the control back. It must be the last statement in the called program.
The parameters can be passed between programs in two ways −
- By Reference
- By Content
Call By Reference
If the values of variables in the called program are modified, then their new values will reflect in the calling program. If BY clause is not specified, then variables are always passed by reference.
Syntax
Following is the syntax of calling subroutine by reference −
CALL sub-prog-name USING variable-1, variable-2.
Example
Following example is the MAIN calling program and UTIL is the called program −
IDENTIFICATION DIVISION. PROGRAM-ID. MAIN. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-STUDENT-ID PIC 9(4) VALUE 1000. 01 WS-STUDENT-NAME PIC A(15) VALUE 'Tim'. PROCEDURE DIVISION. CALL 'UTIL' USING WS-STUDENT-ID, WS-STUDENT-NAME. DISPLAY 'Student Id : ' WS-STUDENT-ID DISPLAY 'Student Name : ' WS-STUDENT-NAME STOP RUN.
Called Program
IDENTIFICATION DIVISION. PROGRAM-ID. UTIL. DATA DIVISION. LINKAGE SECTION. 01 LS-STUDENT-ID PIC 9(4). 01 LS-STUDENT-NAME PIC A(15). PROCEDURE DIVISION USING LS-STUDENT-ID, LS-STUDENT-NAME. DISPLAY 'In Called Program'. MOVE 1111 TO LS-STUDENT-ID. EXIT PROGRAM.
JCL to execute the above COBOL program −
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = MAIN
When you compile and execute the above program, it produces the following result −
In Called Program
Student Id : 1111
Student Name : Tim
Call By Content
If the values of variables in the called program are modified, then their new values will not reflect in the calling program.
Syntax
Following is the syntax of calling subroutine by content −
CALL sub-prog-name USING
BY CONTENT variable-1, BY CONTENT variable-2.
Example
Following example is the MAIN calling program and UTIL is the called program −
IDENTIFICATION DIVISION. PROGRAM-ID. MAIN. DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-STUDENT-ID PIC 9(4) VALUE 1000. 01 WS-STUDENT-NAME PIC A(15) VALUE 'Tim'. PROCEDURE DIVISION. CALL 'UTIL' USING BY CONTENT WS-STUDENT-ID, BY CONTENT WS-STUDENT-NAME. DISPLAY 'Student Id : ' WS-STUDENT-ID DISPLAY 'Student Name : ' WS-STUDENT-NAME STOP RUN.
Called Program
IDENTIFICATION DIVISION. PROGRAM-ID. UTIL. DATA DIVISION. LINKAGE SECTION. 01 LS-STUDENT-ID PIC 9(4). 01 LS-STUDENT-NAME PIC A(15). PROCEDURE DIVISION USING LS-STUDENT-ID, LS-STUDENT-NAME. DISPLAY 'In Called Program'. MOVE 1111 TO LS-STUDENT-ID. EXIT PROGRAM.
JCL to execute the above COBOL program −
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C //STEP1 EXEC PGM = MAIN
When you compile and execute the above program, it produces the following result −
In Called Program
Student Id : 1000
Student Name : Tim
Types of Call
There are two types of calls −
- Static Call occurs when a program is compiled with the NODYNAM compiler option. A static called program is loaded into storage at compile time.
- Dynamic Call occurs when a program is compiled with the DYNAM and NODLL compiler option. A dynamic called program is loaded into storage at runtime.
