Function calls and parameter passing

Functions must be prototyped identically in both C/C++ and Fortran.

In C, by default, all function arguments are passed by value, and the called function receives a copy of the value passed to it. In Fortran, by default, arguments are passed by reference, and the called function receives the address of the value passed to it. You can use the Fortran %VAL built-in function or the VALUE attribute to pass by value. Refer to the XL Fortran Language Reference for more information.

For call-by-reference (as in Fortran), the address of the parameter is passed in a register. When passing parameters by reference, if you write C or C++ functions that call a program written in Fortran, all arguments must be pointers, or scalars with the address operator.