A parameter can be passed by reference (indirect) between C and COBOL. By reference (indirect) means that the actual address of the argument is passed to the called function or procedure; any changes to the parameter made by the called routine can alter the original parameter passed by the calling routine.

To pass data by reference (indirect) from C to COBOL, the variables are passed by C as function arguments, which are pointers to a given type or the address of a given variable, and received by COBOL as BY REFERENCE parameters. Conversely, to pass data by reference (indirect) from COBOL to C, the variables are passed by COBOL as BY REFERENCE arguments and received by the C function as pointers to a given type.

The C function must dereference the pointer to access the actual value. If the value of the pointer is modified by the C function, as opposed to modifying the value that the pointer points to, the results on return to COBOL are unpredictable. Thus, passing values by reference (indirect) from COBOL to C should be used with caution, and only in cases where the exact behavior of the C function is known.

Table 1 shows the supported data types for passing by reference (indirect).