HP 3000 Manuals HP 3000 Manuals
Parameter Passing Methods All arguments of a subprogram written in FORTRAN are passed by reference, except for character variables, which are passed by descriptor. This means that the addresses of the values are passed instead of the actual values of the arguments. Therefore, a FORTRAN subprogram expects a list of addresses for the formal arguments passed to it (for character variables, FORTRAN expects an address and a length), one for each argument and in the order given by the formal argument list contained within the subprogram. Although values are normally passed by reference (indirectly), they can be passed by value (directly) to invoke non-FORTRAN program units that allow passing arguments by value. To accomplish this, use the ALIAS compiler directive to indicate how each of the parameters is to be passed. The language option of the ALIAS directive can also indicate the language of the routine being called so the compiler can pass arguments to the routine in the manner expected. For example, in Pascal, when a formal parameter is a PAC variable (PACKED ARRAY[1..n] OF CHAR), only a pointer to the variable is expected. However, FORTRAN 77 also passes the length of the character variable. If you indicate with the ALIAS directive that the routine being called is a Pascal routine, FORTRAN 77 will not pass the length of the character variable. FORTRAN does not allow arrays to be passed by value. It is not possible to interface a FORTRAN program to a non-FORTRAN program unit that requires an array parameter to be passed by value. Also, as in calling FORTRAN functions that have no parameters, an empty parameter list, ( ), must be given when referencing any non-FORTRAN function that has no parameters.