_ff-addon-tutorial-jsctypes_castingArrays - Shows how to cast arrays.

_ff-addon-tutorial-jsctypes_castingArrays.js

//-------
//doing casting like this crashes: it is the WRONG way

//making integers array like this is wrong, it throws type error, obviously
var my = ctypes.long.ptr.array()([1, 2, 3, 4]);
TypeError: expected type pointer, got 1

// so we make arr like this
var my = ctypes.long.array()([1, 2, 3, 4]);
my.addressOfElement(1).contents; // spits out `Int64 {  }`

my.toString(): "ctypes.long.array(4)([ctypes.Int64("1"), ctypes.Int64("2"), ctypes.Int64("3"), ctypes.Int64("4")])"

// if i do it like this it destroys the remaining elementsi n array, i just get the first element
var cy = ctypes.cast(my, ctypes.int);
cy.toString(): "ctypes.int(1)"

// this way is also the wrong way to cast, it also destroys all after the first element
var cy = ctypes.cast(my, ctypes.int.ptr);
cy.toString(); // this outputs: "ctypes.int.ptr(ctypes.UInt64("0x1"))"

// if do like this accessing elements on it crashes 
var my = ctypes.long.array()([1, 2, 3, 4]);
var my2 = ctypes.cast(my, ctypes.int.ptr.array(4))
//now this line doesnt crash it yet:
my2.addressOfElement(1) // it just spits out `CData { contents: CData }` // i was hoping contents should be same as `my.addressOfElement(1).contents;` but casted
//now this line crashes it:
my2.addressOfElement(1).contents

// -------------------
// after finding an example out there that worked and studying it:


// ok this is something that works, i found this on github, from linux jsctypes, so i need arg 1 and arg2 in the form of this seen here: https://gist.github.com/Noitidart/5a24e8a4f8886ce7bbf6#file-_ff-addon-snippet-x11_windowsmatchingpid-js-L160
ctypes.cast(ctypes.char.ptr(), ctypes.unsigned_long.array(nElements).ptr)

// i figured this out cuz we they did here: ctypes.cast(propData, ctypes.unsigned_long.array(nElements).ptr)
and propData is set to equal new ctypes.char.ptr();


// now this is what i need to get first arg to:
var cy = ctypes.int.ptr()
cy.constructor: CType { targetType: CType, name: "int*", size: 4, ptr: CType, prototype: CData }

// ok now i have to keep going until i can get constructor of first arg i want to pass to ctypes.cast to match cy.constructor

// this is what i have:
var my = ctypes.int.array()([1, 2, 3, 4]); //this is how to make an array of integers
my.constructor: CType { elementType: CType, length: 4, name: "int[4]", size: 16, ptr: CType, prototype: CData }
my.toString(): "ctypes.int.array(4)([1, 2, 3, 4])"

// ok lets try to get the consturctor:
my.constructor: CType { elementType: CType, length: 4, name: "int[4]", size: 16, ptr: CType, prototype: CData }

// this doesnt match constructor of cy.constructor, as we dont have a targetType

//lets try my.address()'s constructor:
my.address().constructor: CType { targetType: CType, name: "int(*)[4]", size: 4, ptr: CType, prototype: CData }

// ok this matches the object seen in cy.constructor!!! 

// ok trying it:
var ry = ctypes.cast(my.address(), ctypes.unsigned_long.array(4).ptr)
ry.constructor: CType { targetType: CType, name: "unsigned_long(*)[4]", size: 4, ptr: CType, prototype: CData }

// so now ry.contents should be ctypes.unsinged_long.array(4)([1, 2, 3, 4])
ry.contents.toString(): "ctypes.unsigned_long.array(4)([ctypes.UInt64("1"), ctypes.UInt64("2"), ctypes.UInt64("3"), ctypes.UInt64("4")])"

// so ry.contents.toString() is casted of my.toString()

// this shows that ry is succesfully casted from my. my type was int and ry type is now unsigned_long

// THEREFORE in conclusion:

var my = ctypes.long.array()([1, 2, 3, 4]); // my.addressOfElement(1).contents; is `Int64 {  }` and my.addressOfElement(1).contents.toString() is `"2"`
var myCasted = ctypes.cast(my.address(), ctypes.int.array(my.length).ptr).contents; // myCasted.addressOfElement(1).contents is now `2`

README

Rev1

• Final write up, contents of tutorial is accurate

Rev2

• Forgot to comment out a comment line, fixed that

Rev3

• Added another wrong way to cast, you might think it works because it doesn't error, but it's wrong as i show by toString()ing it

  • Note: I should update this, in the example i added to show this is wrong it just cuts of the array after first element, however with bigger arrays a simple console.lo would crash it:

    var myXDataLONG = ostypes.LONG.array()(jsarr);
    var myXData = ctypes.cast(myXDataLONG, ostypes.UNSIGNED_CHAR.ptr);
    console.info('myXData:', myXData); // logging after casting is crashing
    

reading string from voidtpr_t cast

var a = ctypes.jschar.array()('hi');
var b = ctypes.cast(a, ctypes.voidptr_t)
var c = ctypes.cast(b.address(), ctypes.jschar.array(3).ptr)
c.contents.readString()



a.toString()
"ctypes.char16_t.array(3)(["h", "i", "\x00"])"
b.toString()
"ctypes.voidptr_t(ctypes.UInt64("0x690068"))"
c.toString()
"ctypes.char16_t.array(3).ptr(ctypes.UInt64("0xce64ad8"))"