Exchanging array between Fortran and C -

i have following c , fortran code exchange data

function exchange_data(data) bind(c,name='exchange_data')     use iso_c_binding     integer(kind=c_int)                                 :: exchange_data     real(kind=c_double), intent(inout), dimension(*)    :: data  end function exchange_data  ....  write(*,*), "sent data c" i=1,numbl     j=1,windspeedcoordnr         write(*, fmt2), global_coord_along_beam(i, j, :)     end end cflag = exchange_data(global_coord_along_beam)  write(*,*), "received data c" i=1,numbl     j=1,windspeedcoordnr         write(*, fmt2), global_coord_along_beam(i, j, :)     end end 

and following test c code:

int exchange_data(double* positions) {      printf("received data fortran");     bladepositions = positions;     (int = 0; < numbld; i++) {         (int j = 0; j < datapointnr; j++) {             printf("[");             (int k = 0; k < 3; k++) {                  printf("%5.4f ", bladepositions[3 * datapointnr * k + 3 * j + i]);                 windspeedalongblade[3 * datapointnr * k + 3 * j + i] = 1.0;             }             printf("]\r\n");         }     }       positions = windspeedalongblade;      printf("data send c");     (int = 0; < numbld; i++) {         (int j = 0; j < datapointnr; j++) {             printf("[");             (int k = 0; k < 3; k++) {                 printf("%5.4f ", positions[3 * datapointnr * k + 3 * j + i]);             }             printf("]\r\n");         }     }     return 0; } 

this has following output

sent data c   -18.6593  -29.1175  137.0735   -18.8588  -29.1308  137.0803   -19.0582  -29.1441  137.0871  received data fortran [-18.6593 -29.1175 137.0735 ] [-18.8588 -29.1308 137.0803 ] [-19.0582 -29.1441 137.0871 ]  data send c [1.0000 1.0000 1.0000 ] [1.0000 1.0000 1.0000 ] [1.0000 1.0000 1.0000 ]  received data c   -18.6593  -29.1175  137.0735   -18.8588  -29.1308  137.0803   -19.0582  -29.1441  137.0871 

i seems can transfer data c function not fortran code. how can achieve that?

the problem following line:

positions = windspeedalongblade; 

doesn't permanently assign windspeedalongblade positions (see here difference between passing value , reference).

to need positions passed pointer array:

int exchange_data(double** positions) {     ...     *positions = windspeedalongblade;     printf("data send c");     (int = 0; < numbld; i++) {         (int j = 0; j < datapointnr; j++) {             printf("[");             (int k = 0; k < 3; k++) {                 printf("%5.4f ", *positions[3 * datapointnr * k + 3 * j + i]);         }             printf("]\r\n");         }     }     return 0; } 

but in case have sure windspeedalongblade remains persistent until use positions.

the simpler solution leave function , assign values of positions array directly:

int exchange_data(double* positions) {      printf("received data fortran");     bladepositions = positions;     (int = 0; < numbld; i++) {         (int j = 0; j < datapointnr; j++) {             printf("[");             (int k = 0; k < 3; k++) {                  printf("%5.4f ", bladepositions[3 * datapointnr * k + 3 * j + i]);                 windspeedalongblade[3 * datapointnr * k + 3 * j + i] = positions[3 * datapointnr * k + 3 * j + i] = 1.0;             }             printf("]\r\n");         }     }      printf("data send c");     (int = 0; < numbld; i++) {         (int j = 0; j < datapointnr; j++) {             printf("[");             (int k = 0; k < 3; k++) {                 printf("%5.4f ", positions[3 * datapointnr * k + 3 * j + i]);             }             printf("]\r\n");         }     }     return 0; } 

so in end depends whether want positions array or pointer array. looks of fortran code seems array, in case second solution best.

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