HP 3000 Manuals HP 3000 Manuals
Transfer of Control The CALL statement is the means used in COBOL programs to pass control from one object program to another, and there are no restrictions on a called program itself calling another object program. Caution should be used, however, to avoid calling a program that preceded, in the calling chain, the program currently having control. Otherwise, results of the run unit are unpredictable. When control is passed to a called program, execution begins either at the first PROCEDURE DIVISION statement or at a secondary entry point of the PROCEDURE DIVISION. Secondary entry points are described later in this chapter under the ENTRY statement, an HP extension to ANSI COBOL'85. Program execution begins at the point of entry to the called program in the normal, line-by-line sequence, following the same conventions used for COBOL main programs. Termination takes place in a COBOL subprogram under two possible conditions. The first condition that causes termination is when an EXIT PROGRAM or GOBACK statement is encountered. When this occurs, control reverts to the calling program, which begins execution at the line immediately following the CALL statement that originally passed control. The second condition that causes termination in a COBOL program is when a STOP RUN statement is encountered. In this case, the entire run unit is terminated. In summary, the EXIT PROGRAM and GOBACK statements terminate only the program in which they appear, while the STOP RUN statement terminates the entire run unit. An exception to this is when a GOBACK statement appears in a main program. In this case, it is equivalent to issuing a STOP RUN statement. If the called program is not a COBOL program, termination of the run unit, or the return of control to the calling program, must be performed in accordance with the rules of the language in which the called program is written.