Technical data

Fortran/C Interface

• When passing the address of a variable, the data representations of the

variable in the calling and called routines must correspond, as shown in

Table 3-3.

• Note that in Fortran, INTEGER and LOGICAL variables occupy 32 bits

of memory by default, but this can be changed by using the –i2 option.

• The Fortran compiler may add items not explicitly speciﬁed in the

source code to the argument list. The compiler adds the following items

under the conditions speciﬁed:

– destination address for character functions, when called

– length of a character variable, when an argument is the address of a

character variable

When a C function calls a Fortran routine, the C function must explicitly

specify these items in its argument list in the following order:

1. If the Fortran routine is a function that returns a character variable of

length greater than 1, specify the address and length of the resultant

character variable.

2. Specify normal arguments (addresses of arguments or functions).

a. The array length must also be passed, as discussed in the next section.

Table 3-3 Equivalent Fortran and C Data Types

Fortran C

integer*2 x short int x;

integer x long int x; or just int x;

logical x long int x; or just int x;

real x ﬂoat x;

double precision x double x;

complex x struct{ﬂoat real, imag;) x;

double complex x struct{double dreal,dimag;} x;

character*6 x char x[6]