Calling an array returning Fortran function from C -

i have existing fortran source code working on adding c to, , having difficulty passing array c fortran function , receiving array back.

it compiles without errors, when attempt run code, says that:

"dimension of array 'p2' (in fortran function) has extent 3 instead of -4537421815 (or other similar number)"

i not sure going on here. attach 2 codes below.

note: have removed lot of variable initialization lines think seems unnecessary finding problem.

c function:

#include <stdio.h> #include <stdlib.h>      extern "c" double* __multiphase_tools_mod_project(double p1[],double *mydt,int *myi,int *myj,int *myk);  extern "c" void cuda_(int *ptr_band, double *ptr_u, double *ptr_v, double *ptr_w) {       double *pt_out;      double pt_in[3];        // loop on domain , compute fluxes near interfaces      //=======================================================================================      //  x face      //=======================================================================================       (k = kmin; k <= kmax; k++)      {           (j = jmin; j <= jmax; j++)           {                (i = imin; <= imax; i++)                {                     if (abs(band[i-1][j][k]) <= nband_cfl && abs(band[i][j][k]) <= nband_cfl )                     {                          (int n = 1; n < 10; n++)                          {                               pt_in[0] = pt[0][n][1];   pt_in[1] = pt[1][n][1];  pt_in[2] = pt[2][n][1];                               pt_out = __multiphase_tools_mod_project(pt_in,&neg_dt_uvw,&i,&j,&k);                          }                     }                }           }      }      return; } 

fortran function:

  function project(p1,mydt,myi,myj,myk) result(p2)     use math     use iso_c_binding     implicit none     real(wp), dimension(3) :: p2     real(wp), dimension(3), intent(in) :: p1     real(wp),               intent(in) :: mydt     integer,                intent(in) :: myi,myj,myk     real(wp), dimension(3) :: v1,v2,v3,v4     v1=get_velocity(p1               ,myi,myj,myk)     v2=get_velocity(p1+0.5_wp*mydt*v1,myi,myj,myk)     v3=get_velocity(p1+0.5_wp*mydt*v2,myi,myj,myk)     v4=get_velocity(p1+       mydt*v3,myi,myj,myk)     p2=p1+mydt/6.0_wp*(v1+2.0_wp*v2+2.0_wp*v3+v4)     return   end function project 

fortran functions return array use hidden argument , implemented subroutines. why can't write compatible c function, because can't portably determine hidden argument properties.

for example

function f() result(res)   real :: res(3)   res = [1.,2.,3.] end 

looks in gcc internal code as

f (struct array1_real(kind=4) & __result) { } 

i suggest convert function subroutine. way can control argument (parameter) array , can make c interface:

  subroutine project(p1,p2,mydt,myi,myj,myk) bind(c)     real(wp), dimension(3), intent(out):: p2     ... 

or can write wrapper subroutine calls function maintain fortran functionality unchanged.