(j3.2006) Should character strings be interoperable with char arrays?
Mon Jul 23 21:29:35 EDT 2007
This is a (random) rant about C Interop based on some codes I was writing
today...just to illustrate the pains of C Interop for strings (which are not
interoperable with char arrays unless LEN=1) and C_LOC.
This is a procedure that writes several variables defined a mesh to a database
file to be read by a visualization software. It takes an array of strings and
an array of arrays (C pointers), one per variable:
void write_point_mesh(const char *filename, int ub, int npts, float *pts,
int nvars, int *vardim, const char * const *varnames,
SUBROUTINE write_point_mesh(filename, ub, npts, pts, nvars, &
vardim, varnames, vars) BIND(C)
CHARACTER(C_CHAR), DIMENSION(*), INTENT(IN) :: filename
INTEGER(C_INT), VALUE :: ub, npts, nvars
REAL(C_FLOAT), DIMENSION(3*npts) :: pts
INTEGER(C_INT), DIMENSION(nvars) :: vardim
TYPE(C_PTR), DIMENSION(nvars) :: varnames
TYPE(C_PTR), DIMENSION(nvars) :: vars
Usage in an actual code requires using CHARACTER arrays instead of strings,
and adding TARGET to all the arrays:
CHARACTER(KIND=C_CHAR), TARGET :: &
CALL write_point_mesh(... varnames=(/C_LOC(v_string), C_LOC(rho_string)/), &
The only way to use the hack we provided to allow strings to be passed as
actuals corresponding to char arrays is to write wrappers.
It should be easier than this!
Aleksandar Donev, Ph.D.
Lawrence Postdoctoral Fellow @ LLNL
High Performance Computational Materials Science and Chemistry
E-mail: donev1 at llnl.gov
Phone: (925) 424-6816 Fax: (925) 423-0785
Address: P.O.Box 808, L-367, Livermore, CA 94551-9900
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