I am working on a game that will have a two dimensional board of dots, each with one boolean attribute (occupied/not occupied). I was thinking the best way to accomplish this is to create a simple c array of Booleans. This will be much more efficient than creating a mutablearray. I'm just confused the best way to accomplish this. The trouble is that I don't know the size of the board until I initialize the board object.
The interface looks like this:
#interface TouchBoard : NSObject{
NSInteger height,width;
BOOL dots[10][10];
}
And the implementation like this:
-(id)initWithHeight:(NSInteger)rows Width:(NSInteger)columns{
if ( self = [super init]){
height = rows;
width = columns;
dots[height][width];
}
return self;
}
Trouble is, in the interface, if i try to declare the dots variable with a dynamic number of indices, dots[][], it'll just give me an error.
Obviously I don't know the size of the array until the object is initialized, but after that it's not going to be changing and only its elements will be changing from true/false.
What is the best way to accomplish this?
In your interface, declares:
BOOL ** dots;
Then, you'll need to use malloc, to dynamically allocate memory:
int i;
dots = malloc( rows * sizeof( BOOL * ) );
for( i = 0; i < rows; i++ )
{
dots[ i ] = calloc( columns, sizeof( BOOL ) );
}
Don't forget to free in your dealloc method:
int i;
for( i = 0; i < rows; i++ )
{
free( dots[ i ] );
}
free( dots );
Related
I have the following code which works fine...
int testarr[3][3] = {
{1,1,1},
{1,0,1},
{1,1,1}
};
[self testCall: testarr];
Which calls this function:
- (void)testCall: (int[3][3]) arr {
NSLog(#"cell value is %u",arr[1][1]);
}
I need the array to be of variable length - What is the best way to declare the function?
Using blanks doesn't work:
- (void)testCall: (int[][]) arr {
Thanks for your help.
I would write this as:
- (void) testCall: (int *) aMatrice;
Doing so allows you to avoid multiple mallocs and the math to calculate a single offset in a linear array based on x, y coordinates in a 2D array is trivial. It also avoids the multiple mallocs implied by int** and the limitations of 2D array syntax perpetuated by the language.
So, if you wanted a 4x5 array, you might do:
#define WIDTH 4
#define HEIGHT 5
#define INDEXOF(x,y) ((y*WIDTH) + x)
int *myArray = malloc(sizeof(int) * 5 * ELEMS_PER_ROW);
You could then initialize the array linearly or with a nested for loop:
for(int x=0; x<width; x++)
for(int y=0; y<height; y++)
myArray[INDEXOF(x,y)] = ... some value ...;
And you would pass it to the method like:
[foo testCall: myArray];
Though you might want to also carry along the width and the height or, better yet, create a IntMatrix subclass of NSObject that wraps all of the pointer arithmetic and storage beyond a nice clean API.
(all code typed into SO)
C arrays can't be variable in more than one dimension.
You can't have this:
int testarr[][] = {
{1,1,1},
{1,0,1,2},
{1,1}
};
But you can have this:
int testarr[][3] = {
{1,1,1},
{1,0,1},
{1,1,1},
{4,5,6},
{7,8,9}
}
foo(testarr);
void foo(int param[][3])
{
printf("%d", param[3][1]); // prints 5
}
You can't use int[][] because the size of the second dimension affects how the array is laid out in memory. If you know the second dimension you can use int[][x], otherwise you'll have to use int** which can be accessed just like an array.
Why don't you just use NSArray or NSMutableArray with NSIntegers? Those array classes are of variable length, and much easier to use.
This would result in
- (void)testCall: (NSArray *) arr {
NSLog(#"cell value is %u", [[arr objectAtIndex:1] objectAtIndex:1]);
}
(Of course, you would also have to define testarr using NSArray.)
If you really want to use C arrays, making the method argument a pointer to an int with
- (void)testCall: (int*) arr {
will probably work (with the rest of the code staying the same).
call
int testarr[3][3] = {
{1,1,1},
{1,0,1},
{1,1,1}
};
[self testCall: (int *)testarr];
function
- (void)testCall: (int *) arr
{
int (*V_arr)[3] = (int(*)[3])arr;
NSLog(#"cell value is %u",V_arr[1][1]);
}
I know this code doesn't work, but how could I actually initialize this correctly?:
NSUInteger highestModelID = 34605;
NSUInteger highestColorID = 328;
NSUInteger** modelColors[highestModelID][highestColorID] = malloc(highestModelID * highestColorID * sizeof(NSUInteger));
So having 2 dynamic depths. I have this massive buffer in a multi-dimensional NSMutableDictionary which hogs memory. I would really love to just do this primitive.
Guess it would be even more amazing to make a class out of this to be able to use it on more places where Objective-C dictionaries and even NSMutableArray are really just overkill. Over time I'm really becoming more and more annoyed by using NSNumber for something that would be super light what I'm used to in golang, suddenly making it a major factor in slowing my app down..
You need this:
NSUInteger* modelColors = malloc(highestModelID * highestColorID * sizeof(NSUInteger));
Which you can use like this:
NSUInteger getModelColor(int modelID, int colorID, int highestModelID, NSUInteger* modelColors) {
return modelColors[colorID * highestModelID + modelID];
}
void setModelColor(NSUInteger color, int modelID, int colorID, int highestModelID, NSUInteger* modelColors) {
modelColors[colorID * highestModelID + modelID] = color;
}
Basically this is a 2D array, where modelID indexes the rows, and colorID indexes the columns (assuming row-major layout).
The way of creating it isn't really that different from creating NSArray of NSArrays. You need to alloc array of NSUInteger* first, then alloc each of its elements.
NSUInteger **modelColors;
modelColors = malloc(highestModelID * sizeof(NSUInteger*));
for (int i = 0; i < highestModelID; i++) {
modelColors[i] = malloc(highestColorID * sizeof(NSUInteger));
}
I cannot seem to solve this problem, im not sure what it is at this point but the tread error wont go away. I cant seem to find what im doing wrong.
This code may be a handful to read (sorry) but its very simple. I'am basically invoking a function from main and passing an array of function values, from there im passing two fractions at a time to a method so it find the LCM(least common multiple) using the denominators and return the value. But a thread error seems to be occurring at the call to the findLCM method from function at the point of where the method is declared.
#interface Fraction: NSObject
#property int numerator, denominator;
-(Fraction *)findLCM:(Fraction *)fraction withXFractions:(int)Xfraction;
#implementation Fraction
-(Fraction *)findLCM:(Fraction *)fraction withXFractions:(int)Xfraction{
int lcmOfFraction = 0;
int a, b;
a = fraction.denominator;
b = self.denominator;
int max =(a>b) ? a : b; // get max value out of the two denominators.
for (int i = 0; i < Xfraction; i++) {
while(1) /* Always true. */
{
if(max%a==0 && max%b==0)
{ lcmOfFraction = max;
break; /* while loop terminates. */
}
++max;
}
}
Fraction *lcmDenominator = [Fraction new];
[lcmDenominator setTo:0 over:max]; //passing just LCM (denominator of 2 fractions)
return lcmDenominator;
}
Fraction *addFraction(Fraction **arrayOfFractions, int arraySize) {
Fraction *LCM = [[Fraction alloc] init];
int lcmOfFractions = 0;
[LCM setTo:0 over:1];
for (int i = 0; i <= arraySize; i++) {
LCM = [LCM findLCM:arrayOfFractions[i] withXFractions:4];
//^gets the LCM (the common denominator)
}
return LCM;
}
int main () {
#autoreleasepool {
[frac1 setTo:2 over:12]; [frac2 setTo:2 over:4];
[frac3 setTo:6 over:8]; [frac4 setTo:8 over:3];
Fraction __autoreleasing *arrayOfFractions[4] = {frac1, frac2, frac3, frac4 };
Fraction *LCMFraction = addFraction(arrayOfFractions, 4);
//common LCM return
}
}
You create no threads in this code. When asking a question like this you should clearly explain what the error is, and what you have tried to find its source. People may then be able to help you.
Some hints/suggestions:
use breakpoints to stop your code during execution to allow you to examine the values of your variables
pay close attention to indexing operations, you are using a C array and those do not do bounds checking
ask whether using a C array here, rather than an NSArray is your best choice. Note there is nothing wrong with using C arrays when appropriate.
__autoreleasing probably doesn't mean what you think it does, it is rare to see this used explicitly in user code.
If you have a specific question when you've got further ask a new question on SO, somebody will probably be able to help you out.
HTH
I bumped to a strange error.(at least for me) I am trying to use float array in FFT and audio filters that I apply. but float array gives different datas at the end.
I define a global pointer. I point a float array to it. but when I try to use the pointer in somewhere out of the scope of a method, the last 100-150 datas of 441000 datas get mostly 0 or some other very big numbers. I dont understand how a data can change when I use somewhere in out of scope
in scope I loop in it and every data is correct but when I try to loop outside of the scope of the method I created the array, it gives different datas at the end.
#interface ViewController ()
{
float *filteredData;
int theFileLengthInFrames;
}
#end
#implementation ViewController
..
..
-(void)FilterData:(float * ) rawData
{
int count = theFileLengthInFrames;
float filteredRawData[count];
for (int i = 0; i<count; i++)
{
filteredRawData[i] = rawData[i];
printf("%d_%f ",i,filteredRawData[i]);
//I check here to see the data . In here it is normal
}
filteredData = filteredRawData;
}
-(void) CalculateFFT
{
int numSamples = theFileLengthInFrames;
for (int i = 0; i<numSamples; i++)
{
printf("%d_%f ",i,filteredData[i]);
//when I check here to see the data , the last around 100 data are 0.00000 or some big number such as 250399682724883753288597504.000000
}
}
need help thanks
Your FilterData: method points the instance variable filteredData to a local array filteredRawData. Since filteredRawData is allocated on the stack, it becomes invalid when FilterData: returns. Then filteredData is a dangling pointer, and using it results in undefined behavior.
Solution: allocate persistent storage for filteredData. I would do it like this:
#implementation ViewController {
NSMutableData *filteredDataStorage;
float *filteredData;
}
-(void)FilterData:(float * ) rawData {
int count = theFileLengthInFrames;
filteredDataStorage = [NSMutableData dataWithLength:count * sizeof *rawData];
filteredData = (float *)filteredDataStorage.mutableBytes;
for (int i = 0; i<count; i++) {
filteredRaw[i] = rawData[i];
printf("%d_%f ",i,filteredRawData[i]);
//I check here to see the data . In here it is normal
}
}
Using NSMutableData for the persistent storage lets ARC take care of deallocating it when you call FilterData: again, or when ViewController is deallocated.
filteredData - The float pointer is an ivar, it's scoped to your object instance.
filteredRawData is defined at method scope. It's an array located on the stack. When filteredRawData goes out of scope that memory is no longer valid. Reading from it is undefined at best and could result in an access violation. You probably want to use malloc to dynamically allocate memory for your data, or have a global buffer defined for you to play with.
Is there a way to declare a 2D array of integers in two steps? I am having an issue with scope. This is what I am trying to do:
//I know Java, so this is an example of what I am trying to replicate:
int Array[][];
Array = new int[10][10];
Now, in OBJ-C I want to do something similar, but I cant get the syntax right. Right now I have it in one step, but I cannot use it outside of the If-Statement in which I currently have it:
int Array[10][10]; //This is based on an example I found online, but I need
//to define the size on a seperate line than the allocation
Can anyone help me out with this? I know its probably a more basic question, but you can't use the keyword "new" outside of a message (to my knowledge) and you cant send messages to ints. :(
*EDIT 1:**
My problem is scope related.
//Declare Array Somehow
Array[][] //i know this isn't valid, but I need it without size
//if statement
if(condition)
Array[1][2]
else
Array[3][4]
//I need to access it outside of those IFs
//... later in code
Array[0][0] = 5;
This is my preferred way of creating a 2D array, if you know the size of one of the boundaries:
int (*myArray)[dim2];
myArray = calloc(dim1, sizeof(*myArray));
And it can be freed in one call:
free(myArray);
Unfortunately, one of the bounds MUST be fixed for this to work.
However, if you don't know either of the boundaries, this should work too:
static inline int **create2dArray(int w, int h)
{
size_t size = sizeof(int) * 2 + w * sizeof(int *);
int **arr = malloc(size);
int *sizes = (int *) arr;
sizes[0] = w;
sizes[1] = h;
arr = (int **) (sizes + 2);
for (int i = 0; i < w; i++)
{
arr[i] = calloc(h, sizeof(**arr));
}
return arr;
}
static inline void free2dArray(int **arr)
{
int *sizes = (int *) arr;
int w = sizes[-2];
int h = sizes[-1];
for (int i = 0; i < w; i++)
free(arr[i]);
free(&sizes[-2]);
}
The declaration you showed (e.g. int Array[10][10];) is OK, and will be valid for the scope it was declared to, if you do it in a class scope, then it will be valid for the whole class.
If the size of the array varies, either use dynamic allocation (e.g. malloc and friends) or use NSMutableArray (for non-primitive data types)