Passing strings and allocatable arrays in a structure between C++ and Fortran

I have a situation where I want to pass a struct from C++ to Fortran. Every test type (double, int, bool, defined arrays) works except allocatable arrays. But it is strange that they only don't work when there is a string member of the structure. When I remove the string member, it works. Here is my code:

C++:

#include <iostream>
#include <cstddef>
#include <vector>

using namespace std;
struct t_nwork {
        double  treal;
        int     tint;
        bool    tlog;
        double  trealarr[10];
        string  tchar;
        double *trealalloc;
};

//Fortran subroutine definition
extern "C" {
    void nf90(t_nwork *net);
}
    
int main()
{
    t_nwork net;
    net.tchar = "Dick";
    net.trealalloc = new double[5];
    for (int i = 0; i < 5; i++ ){
       net.trealalloc[i] = (double) i * 3;
    }
    nf90(&net);
}

Fortran:

module netf90_mod

implicit none

  type :: t_nwork
    real(8)      :: treal
    integer      :: tint
    logical      :: tlog
    real(8)      :: trealarr(10)
    character(4) :: tchar
    real(8), allocatable :: trealalloc(:)
  end type

contains
  subroutine nf90(net) bind(c)
    use iso_c_binding

    type(t_nwork), intent(inout) :: net
    write(6,*) net%tchar
    write(6,*) size(net%trealalloc)
    write(6,*) net%trealalloc(0)
    write(6,*) net%trealalloc(1)
    write(6,*) net%trealalloc(2)
    write(6,*) net%trealalloc(3)
    write(6,*) net%trealalloc(4)
  end subroutine

end module

If I comment out the string (tchar) member in all occurrences then the allocatable array gets passed through ok (well the length is 0 but the 5 values come through). But with it in there, it does not work.

I compile and link under Intel:

icx -c testc.cpp
ifort testc.obj testf.f90 

I'm no CPP expert, so maybe I haven't got the syntax quite correct.