is it possible to declare a variable length array with global scope in objective-c?
I'm making a game with a world class, which initializes the world map as a three dimensional integer array. while it's only a two dimensional side scroller, the third dimension of the list states which kinda of block goes at the coordinate given by the first two dimensions
after the initialization function, a method nextFrame: is scheduled (I'm using cocos2d and the CCDirector schedule method). I was wondering how to pass the int[][][] map array from the initialization function to the nextFrame function
I tried using global (static keyword) declaration, but got an error saying that global arrays cannot be variable length
the actual line of code I'm referring to is:
int map[xmax][ymax][3];
where xmax and ymax are the farthest x and y coordinates in the list of coordinates that defines the stage.
I'd like to somehow pass them to nextFrame:, which is scheduled in
[self schedule:#selector(nextFrame:)];
I realize I can use NSMutableArray, but NSMutableArray is kinda a headache for 3-dimensional lists of integers (I have to use wrapper numbers for everything...). is there any way to do this with integer arrays?
You can't have a statically allocated global array of dynamic dimensions in C (of which Objective C is a clean superset). But you can use a global array of any length or size (up to available memory) at runtime by using a global pointer, malloc, and array indexing arithmetic.
static int *map = NULL;
...
map = malloc (dim1 * dim2 * dim3 * sizeof(int)); // in some initialization method
if (map == NULL) { /* handle error */ } // before first array access
...
myElement = map[ index3 + dim2 * ( index2 + dim1 * index1 ) ]; // some macro might be suitable here
Or you could make Objective C getter and setter methods that checks the array and array bounds on every access, since a method can return plain C data types.
Another option, if you know the max dimensions you want to have available and are willing to use (waste) that amount of memory, is to just statically allocate the max array, and throw an exception if the program tries to set up something larger than your allowed max.
I tried using global (static keyword)
declaration, but got an error saying
that global arrays cannot be variable
length
But global array pointers can point to arrays of variable length.
Related
I have a C mex routine that is iterating over subfields of a structure. Sometimes calling mxGetFieldByNumber() returns NULL when mxGetFieldNameByNumber() returns a string for the same field idx. Here is a toy:
numFields = getNumberOfFields( currentField );
for( fieldIdx = 0; fieldIdx < numFields; fieldIdx ++){
subField = mxGetFieldByNumber( currentField, 0 , fieldIdx );
fieldName = mxGetFieldNameByNumber(currentField, fieldIdx );
}
I have read through the documentation of both functions. A NULL can be returned if (in this example) currentField were not a mxArray which I know is not the case because mxGetFieldNameByNumber() returns something sensible. Insufficient heap space could be the problem but I've checked that and it is on 400kb. NULL can also be returned when no value is assigned to the specified field but I've looked and it appears the value is zero.
Any thoughts?
When a struct is created at the MATLAB level or in a mex routine via mxCreateStruct, not all field elements are necessarily populated. In such case, MATLAB physically stores a NULL pointer (i.e., 0) in those data spots (a struct is essentially an array of mxArray pointers). E.g., take the following code snippet assuming X doesn't exist yet:
X.a = 5;
X(2).b = 7;
The X struct variable actually has four elements, namely X(1).a, X(1).b, X(2).a, and X(2).b. But you only set two of these elements. What does MATLAB do with the other elements? Answer: It simply stores NULL pointers for those spots. If you subsequently access those NULL spots in your MATLAB code, MATLAB will simply create an empty double matrix on the fly.
At the mex level, a similar thing happens. When you first create the struct with mxCreateStruct, MATLAB simply fills all of the element spots with NULL values. Then you can populate them in your code if you want, but note that leaving them as NULL is perfectly acceptable for returning back to MATLAB. The routine mxGetFieldByNumber actually gets the element mxArray pointer, and mxGetFieldNameByNumber gets the name of the field itself ... two very different things. If you get a NULL result from a valid mxGetFieldByNumber call (i.e. your index is not out of range), that simply means this element was never set to anything. You should never get a NULL result from a valid mxGetFieldNameByNumber call, since all field names are required to exist.
If you were to pass in the X created above to a mex routine and then examine prhs[0] you would find the following:
mxGetFieldByNumber(prhs[0],0,0)
returns a pointer to an mxArray that is the scalar double 5
mxGetFieldByNumber(prhs[0],0,1)
returns a NULL pointer
mxGetFieldByNumber(prhs[0],1,0)
returns a NULL pointer
mxGetFieldByNumber(prhs[0],1,1)
returns a pointer to an mxArray that is the scalar double 7
mxGetFieldNameByNumber(prhs[0],0)
returns a pointer to the string "a"
mxGetFieldNameByNumber(prhs[0],1)
returns a pointer to the string "b"
In the Swift Language Reference, under String Mutability it says:
You indicate whether a particular String can be modified (or mutated) by assigning it to a variable (in which case it can be modified), or to a constant (in which case it cannot be modified)
It's unclear to me if the "it" that is mutable is the variable or the value.
For example, if I write:
var s = ""
for i in 0...100 {
s += "a"
}
Is it akin to creating an NSMutableString and calling appendString 100 times (i.e. linear cost)?
Or is it akin to creating a series of ever-larger NSString instances and combining them with stringByAppendingString (i.e. quadratic cost)?
Or perhaps it creates some kind of rope structure behind the scenes, so it's immutable and linear in aggregate?
Appending to a collection like this (while String is not itself a collection, you're essentially appending to its characters view with that code) is linear, not quadratic. A string in Swift has an internal buffer whose size is doubled whenever it fills up, which means you will see fewer and fewer reallocations as you repeatedly append. The documentation describes appending in this way as an "amortized" O(1) operation: most of the time appending is O(1), but occasionally it will need to reallocate the string's storage.
Arrays, sets, and dictionaries have the same behavior, although you can also reserve a specific capacity for an array (using reserveCapacity(_:)) if you know you'll be appending many times.
All these collections use "copy-on-write" to guarantee value semantics. Here, x and y share a buffer:
let x = "a"
let y = x
If you mutate x, it gets a new, unique copy of the buffer:
x += "b"
// x == "ab"
// y == "a"
After that, x has its own buffer, so subsequent mutations won't require a copy.
x += "c" // no copy unless buffer is full
My Situation:
I have learnt Swift for a while and Swift is my only language I've learnt for iOS Development, which means I did not learn Objective-C Systematically. I can just read OC Code a little.
I got a CGPoint problem when I tried to translate a OC project to Swift project.
Objective-C Code:
- (void)drawFramesetter:(CTFramesetterRef)framesetter
attributedString:(NSAttributedString *)attributedString
textRange:(CFRange)textRange
inRect:(CGRect)rect
context:(CGContextRef)c
{
.
.
CTFrameRef frame = CTFramesetterCreateFrame(framesetter, textRange, path, NULL);
CFArrayRef lines = CTFrameGetLines(frame);
NSInteger numberOfLines = CFArrayGetCount(lines);
CGPoint lineOrigins[numberOfLines]; // *** The place I had been obstructed! ***
.
.
.
}
My Question:
I have no idea why this line of code, declared as CGPoint lineOrigins[numberOfLines], have no * to create an instance variable, lineOrigins ?
My unproven guess is that CGPoint is a struct rather than a Class, but it's still so mysterious to me that created an instance variable without * and =.
Another point confused me is [numberOfLines]. Is [numberOfLine] an array?
Please teach me how to translate CGPoint lineOrigins[numberOfLines]; into Swift or show me some hints.
An big appreciation for your guide and time.
Ethan Joe
The line
CGPoint lineOrigins[numberOfLines];
Creates a C array of CGPoint objects.
It's written inside a function, so it creates a local (stack) variable.
That code will only compile if numberOfLines is a compile-time constant, because the compiler has to allocate a fixed amount of space for your array on the stack at compile time.
C structs are simple "templates" that interpret a block of memory as containing one or more scalar values. The values are stored sequentially in memory.
A C array is also a way of looking at a block of memory, as a sequential series of one or more scalar "things." Those scalar things can be simple scalars like integers, or they can be structs.
When you define a C array like in your example, the compiler makes memory space for the full array, and sets the variable to a pointer to the first element.
The type of lineOrigins is actually type "pointer to CGPoint". In C, an array type and a pointer to an object of that type are interchangeable. It is a bit like a Swift unsafe buffer pointer. There's no range checking.
EDIT:
A similar Swift declaration would be:
var lineOrigins = [CGPoint]()
or, to pre-fill it with a bunch of zero points:
var lineOrigins = [CGPoint](count: numberOfLines, repeatedValue: CGPointZero)
CGPoint is a C struct, which should translate into a C structure.
CGPoint lineOrigins [...] is a local variable named lineOrigins, which is an array of struct CGPoint.
CGPoint lineOrigins [numberOfLines] is a local variable named lineOrigins, which is an array of struct CGPoint with numberOfLines elements.
There is an array init method where you pass the number of array elements, and one array element which is duplicated.
I'm trying to constrain an entire object (not just the fields of an object) based on some other object. Here is a stripped down version of my production code:
I have the following class:
class some_class;
bit[7:0] some_field;
bit[3:0] some_other_field;
// this function would do some complex procedural
// operations on the fields of the object
function void do_some_op();
bit[3:0] tmp = some_field[3:0];
some_field[3:0] = some_other_field;
some_other_field = some_field[7:4];
some_field[7:4] = tmp;
endfunction
function some_class some_function(bit some_param);
some_function = new this;
$display("foo"); // this print here to see that method is executed
if (some_param)
some_function.do_some_op();
endfunction
function void print();
$display("some_field = %x", some_field);
$display("some_other_field = %x", some_other_field);
endfunction
endclass // some_class
This class contains some integral fields. It also has a method that does some complex procedural on the fields of that class. In the example I've simplified it. I also have another class that returns a new object on which the operation has been performed.
I have another class that operates with some_class instances. As per Dave's input I have made it create the objects first (as randomize() does not create objects).
class some_shuffler;
rand bit params[];
rand some_class objects[];
constraint size_c {
params.size() == objects.size() - 1;
params.size() <= 10;
};
constraint shuffle_c {
// not allowed by standard
// foreach (params[i])
// objects[i+1].some_field == objects[i].some_function(params[i]);
foreach (params[i])
objects[i+1].some_field ==
objects[i].some_function(params[i]).some_field &&
objects[i+1].some_other_field ==
objects[i].some_function(params[i]).some_other_field;
};
function new();
objects = new[10]; // create more objects than needed
foreach (objects[i])
objects[i] = new();
// initialize first object
objects[0].some_field = 8'hA5;
endfunction // new
function void post_randomize();
foreach (objects[i]) begin
$display("objects[%0d]:", i);
objects[i].print();
$display("");
end
endfunction
endclass
This class has two arrays, one of operations performed and one of the intermediate states. There is an initial object. On this one, some_function is performed and it results in the next object.
This is how I wanted to test it:
module top;
import some_pkg::*;
initial begin
static some_shuffler shuffler = new();
bit rand_ok;
rand_ok = shuffler.randomize() with {
params.size() == 1;
};
assert (rand_ok);
end
endmodule
When trying to constrain the objects directly I immediately get a constraint violation. The simulator seems to try to make the 2 handles equal. This is anyway forbidden by the standard and I'm not doing it anymore (though a compile failure would have been nice). I've unraveled the constraints as suggested by Dave and Greg (I think doing some_function().some_field is non-standard, but it compiles in Questa).
Even now, the foo print does not appear on the command line (some_function() is not getting executed). What I see is that objects[1] contains the initial value (all 0s for both fields).
I can't just generate the list of params and then procedurally randomize the objects for each iteration, because I want to be able to constrain the last object to have a certain value - basically giving the constraint solver the start and the end points and let it figure out the way to get there.
Object vs. object constraints are not allowed in SystemVerilog because they are not integral types. See IEEE Std 1800-2012 § 18.3:
Constraints can be any SystemVerilog expression with variables and constants of integral type (e.g., bit, reg, logic, integer, enum, packed struct).
You can constrain the integral components of class object if the component is a rand (ex obj[1].value == obj[0].value+1;).
Functions are allowed in constraints, but there limitation. See IEEE Std 1800-2012 § 18.5.12 Functions in constraints for full details. Limitations include:
Functions cannot contain output or ref arguments
Functions should be automatic and leave no side effects
The functions arguments have an implicit priority (ex x<=F(y) infers solve y before x)
Circular dependencies will result in an error
Update:
Looks like the only thing truly being randomized is params. The values of some_field and some_other_fieldare calculations. So it makes more sense to move the loop for shuffling into thepost_randomize` function.
constraint size_c {
params.size() == objects.size() - 1;
params.size() <= 10;
};
function void postrand_shuffle();
foreach (params[i])
objects[i+1] = objects[i].some_function(params[i]);
endfunction
function void post_randomize();
postrand_shuffle();
// ... your other post_rand code...
endfunction
SystemVerilog's random constraint solver will work when there is at least one solution. However when the solution space is small and difficult to determine or a long chain, simulator performance drops. For these scenarios it is better move the one-to-one sequential calculations into post_randomize.
A couple of problems with your example code.
Objects must be constructed first before calling randomize(). If
you know the exact size before calling randomize (like in your
example), just new[n] the dynamic arrays constructing each object
element first, and remove the size constraints. If the size will be
random, you need an upper limit constraint on the size. construct the max
number of objects before calling randomize(), and after randomizing the array, the unused objects will be eliminated.
Constraint expressions must be integral. You can do objects[i+1].some_field == objects[i].some_field but the solver cannot manipulate class handles.
The return values of functions are treated as state variables. Move these to post_randomize
This is a superfluous question. Is there any dynamic array or list in Progress 10.2B?
Example:
I create a base class called "InventoryTransaction". I read a MSSQL table from Progress and I would like to create an instance of InventoryTransaction class for each record found then add it to a "list/array" so I can later process them.
Is there something like MyArray:Add(MyItem) that will increase automatically the array size +1 then will add the instance of MyItem to the array?
I discovered the function EXTENT to set a size dynamically to an array but I do not know the count before reading all the transaction in the MSSQL table. Alternatively, I could execute a "select count(*) from MyTable" before reading all the transaction to retrieve the count and then extent the array.
Thank you!
Happy friday!
Sebastien
You can create "indeterminate" arrays. i.e.
define variable x as decimal extent no-undo.
An indeterminate array variable can be in one of two states: fixed or unfixed, meaning it either has a fixed dimension or it does not. An indeterminate array variable has an unfixed dimension when first defined. You can fix the dimension of an indeterminate array variable by:
Initializing the array values when you define the variable,
Using the INITIAL option
Setting the number of elements in the array variable
Using the EXTENT statement
Assigning a determinate array to the indeterminate array, fixing it to the dimension of the determinate array
Passing array parameters to a procedure, user-defined function, or class-based method, so that the indeterminate array variable is the target for the passing of a determinate array, fixing the indeterminate array to the dimension of the determinate array
Once fixed, ABL treats a fixed indeterminate array as a determinate array.
I just discovered progress.lang.object:
FILE: array.p
/* declaration */
DEFINE TEMP-TABLE arrITem
FIELD Item AS CLASS PROGRESS.lang.OBJECT.
DEFINE VARIABLE oItem AS CLASS Item NO-UNDO.
DEFINE VARIABLE i AS INTEGER NO-UNDO.
/* create 10 products */
DO i = 1 TO 10:
CREATE arrItem.
arrItem.Item = NEW Item("Item_" + STRING(i), "Description_" + STRING(i)).
END.
/* display object information */
FOR EACH arrItem:
ASSIGN oItem = CAST(arrItem.Item,Item).
DISPLAY oItem:ItemNo.
END.
FILE: item.cls
CLASS Item:
DEFINE PUBLIC PROPERTY ItemNo AS CHARACTER
GET.
SET.
DEFINE PUBLIC PROPERTY DESCRIPTION AS CHARACTER
GET.
SET.
/* constructor */
CONSTRUCTOR PUBLIC Item():
END.
CONSTRUCTOR PUBLIC Item(
INPUT strItemNo AS CHARACTER
,INPUT strDescription AS CHARACTER
):
ASSIGN ItemNo = strItemNo.
ASSIGN DESCRIPTION = strDescription.
END.
END CLASS.
Thank you!
Sebastien
The short answer is - no, the 10.2B AVM doesn't allow you to dynamically resize an array.
The long answer is you could (a) add the object to a linked list of objects, or (b) create a temp-table with a Progress.Lang.Object field, create a new TT record for each object instance you want to track, and assign the object's pointer to the TT's PLO field.