If you can tell me, why you should use array for that purpose?
In C/C++, a string is array of char, you can pass a string pointer from C/C++ to parameter.

FUNCTION your_ole_func(tcBuffer AS STRING @) AS any
  ...
ENDFUNC


*!* this is calling from vfp
lcBuffer = REPLICATE(CHR(0), lnSize)
your_ole_func(@lcBuffer)

DIMENSION laBuffer[ lnSize ]
FOR i = 1 TO lnSize
  laBuffer[ i ] = SUBSTR(lcBuffer, i, 1)
ENDFOR


*!* this is calling from C/C++
char *cBuffer = malloc(..
your_ole_func(cBuffer);

for( i = 0; i < nSize; i++) {
  ... = cBuffer[ i ];
}

I didn't test it, I hope that correct and solve your problem.