how to access common block data from c

[lizhiling98]

I am doing a mixed c/fortran project and has a problem for accessing fortran common block from c

uisng the intel fortran mixed language example as below.

There is a common block kwaves in fortran program, and I want to access the data x, y in c++ program, when I debug this project, in the c subroutine, I can see that the kwaves has the address, but it does not show as a struct and I can not access to its data. Anyone know why?

zhiling LI

Fortran part:

PROGRAM fmain
IMPLICIT NONE

INTERFACE
SUBROUTINE c_routine (int_arg, str_in, str_out) BIND(C)
USE,INTRINSIC :: ISO_C_BINDING ! Declares C kinds
INTEGER(C_INT), VALUE,INTENT(IN) :: int_arg
CHARACTER(KIND=C_CHAR),DIMENSION(*) :: str_in,str_out
END SUBROUTINE c_routine
END INTERFACE
real*8 x, y
!DEC$ ATTRIBUTES alias :'kwaves'::kwaves

common /kwaves/ x, y

CHARACTER(80) OUTPUT_TEXT
INTEGER IN_ARG, OUTPUT_LEN
CHARACTER(80) INPUT_TEXT

INPUT_TEXT = "Testing..."C ! C suffix adds a null terminator
IN_ARG = 123

x=1.0
CALL c_routine (in_arg, input_text, output_text)

OUTPUT_LEN = INDEX(OUTPUT_TEXT," ")
IF (OUTPUT_LEN == 0) OUTPUT_LEN = 80

WRITE (*,*) OUTPUT_TEXT(1:OUTPUT_LEN)

END

C part

#include
#pragma pack(2)

extern struct kwaves_type
{
double x, y;
}kwaves;
#pragma pack()

extern "C" void c_routine (
int int_arg,
char* input_text,
char* output_text//,
//struct kwaves_type *kwaves1
)

{
sprintf(output_text,"%s%i ",input_text,int_arg);
}

[IanH · Accepted solution]

Add extern "C" to the declaration of the struct on the C++ side.

Consider using BIND(C) to specify the external name of the common block. This should also remove any need to go a #pragma pack'ing. Consider using C_DOUBLE as the kind of the reals that are in the common block.

Note that you can interop with normal module variables too. Common blocks are an anachronism.

[lizhiling98]

thanks. it solve my problem.

Best wishes,
Zhiling LI