Unable to pass string array inside structure to a C function using FFI

Question

I am trying to pass a string array to my C function using FFI as

var ffi = require('ffi');
var ref=require('ref');
var ArrayType = require('ref-array');
var Struct = require('ref-struct');

var StringArray = ArrayType('string');
var myStructure=Struct({
'ulonglong' : ref.types.ulonglong,
'charptrptr' : StringArray,
'stringArr' : StringArray
});

var structObjNew=new myStructure();
structObjNew.ulonglong=123456;
structObjNew.charptrptr=["sample","ptrptr"]; 
structObjNew.stringArr=["sample1","ptrptr1"];

var libfactorial = ffi.Library('./stringArray', {
 'readArray': [ 'string', [ myStructurePtr]] //creating header definition 
});

var output=libfactorial.readArray(structObjNew.ref()); 

.C file for the above code

struct myStructure
 {
    unsigned long long ulonglong;
    char  **charptrptr;
    char stringArr[3][10];
 };
EXPORT char* readArray(struct myStructure *nameofstr) {
  printf("Value from first param from structure of type char**\n");
  printf("%s\n",nameofstr->charptrptr[0]);
  printf("%s\n",nameofstr->charptrptr[1]);

  printf("value form second param from structure of thype char[][]\n");
  printf("%s\n",nameofstr->stringArr[0]);
  printf("%s\n",nameofstr->stringArr[1]);
}

I am getting output like:

• The value of the first param from structure of type char**

  Sample: ptrptr

• The value of the second param from a structure of type char[][]

  Any garbage value like ▲é┌

Ie When I am passing an array to char** type then I am getting a correct output, but when I am trying to pass it to char*[] or char[][] format declared inside structure , I am getting a garbage value.

But directly passing string array like ["aa","bb"] to char*[] parameter in C works fine. It is not working for me when I am using it inside a structure.

Answer 1

Your second array has a fixed size of chars.

Give this a try:

var CharArray10 = ArrayType('char', 10)
var StringArray3 = ArrayType(CharArray10, 3)

var myStructure = Struct({
  'ulonglong' : ref.types.ulonglong,
  'charptrptr' : StringArray,
  'stringArr' : StringArray3
});

More examples here