Structures, COMPLEX, and LOGICAL Types

Visual Studio 6.0

The Fortran structure variable, defined with the STRUCTURE keyword and declared with the RECORD statement, is equivalent to C struct declarations. You can pass structures by value or by reference. Be careful, however, about the effect of structure alignment if you are going to share structures.

C, C++, and MASM do not directly implement the Fortran types COMPLEX*8 and COMPLEX*16. However, you can write structures that are equivalent. The type COMPLEX*8 has two fields, both of which are 4-byte floating-point numbers; the first contains the real-number component, and the second contains the imaginary-number component. The type COMPLEX is equivalent to the type COMPLEX*8. The type COMPLEX*16 is similar to COMPLEX*8. The only difference is that each field of COMPLEX*16 contains an 8-byte floating-point number.

Note   Fortran functions of type COMPLEX place a hidden COMPLEX argument at the beginning of the parameter list. C functions that implement such a call from Fortran must declare this argument explicitly, and use it to return a value. The C return type should be void.

Here are the C/C++ structure definitions for the Fortran COMPLEX types.

struct complex8 {
    float   real, imag;
};

struct complex16 {
    double  real, imag;
};

A Fortran LOGICAL*2 is stored as a 1-byte indicator value (1=true, 0=false) followed by one unused byte. A Fortran LOGICAL*4 is stored as a 1-byte indicator value followed by three unused bytes. The type LOGICAL is equivalent to LOGICAL*4.

To pass or receive a Fortran LOGICAL type, use an integer. Note that only the low byte is tested or used by Fortran.

The C++ class type has the same layout as the corresponding C struct type, unless the class defines virtual functions or has base classes. Classes that lack those features can be passed in the same way as C structures.

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