Arrays of strings in Fortran-C bridges using iso_c_binding

Question

I\'m writing code that will call a C function from Fortran using Fortran\'s C interoperability mechanism (introduced in Fortran 2003 and implemented in newer versions of gfo

Answer 1

The way we do it is to use a C_PTR array to point to strings. For example:

CHARACTER(LEN=100), DIMENSION(numStrings), TARGET :: stringArray
TYPE(C_PTR), DIMENSION(numStrings) :: stringPtrs

then we set our strings in stringArray, remembering to null-terminate them such as:

DO ns = 1, numStrings
   stringArray(ns) = "My String"//C_NULL_CHAR
   stringPtrs(ns) = C_LOC(stringArray(ns))
END DO

and pass stringPtrs to the C function.

The C function has the interface:

void stringFunc(int *numStrings, char **stringArray) {
    int i;
    for(i=0;i<*numStrings;++i) {
       printf("%s\n",stringArray[i]);
    }
 }