Technical data

Fortran/C Interface

Note that only one main routine is allowed per program. The main routine

can be written in either C or Fortran. Table 3-1 contains an example of a C

and a Fortran main routine.

Invocations

Invoke a Fortran subprogram as if it were an integer-valued function whose

value speciﬁes which alternate return to use. Alternate return arguments

(statement labels) are not passed to the subprogram but cause an indexed

branch in the calling subprogram. If the subprogram is not a function and

has no entry points with alternate return arguments, the returned value is

undeﬁned. The Fortran statement

call nret (*1,*2Ex,*3)

is treated exactly as if it were the computed goto

goto (1,2,3), nret()

A C function that calls a Fortran subprogram can usually ignore the return

value of a Fortran subroutine; however, the C function should not ignore the

return value of a Fortran function. Table 3-2 shows equivalent function and

subprogram declarations in C and Fortran programs.

Table 3-1 Main Routines

C Fortran

main () {

printf("hi!\n");

}

write (6,10)

10 format ('hi!')

end

Table 3-2 Equivalent C and Fortran Function Declarations

C Function Declaration Fortran Function Declaration

double dfort() double precision function dfort()

double rfort() real function rfort()

int ifort() integer function ifort()

int lfort logical function lfort()