How would I go about copying the content of a pointer to an array to a temporary pointer to an array, and then making the original pointer point to the same thing the temporary pointer is pointing too? In code form, :
bankAccount **array = new bankAccount* [maxSize];
bankAccount **temp = new bankAccount* [maxSize + 5];
for(int i = 0; i < maxSize; i++)
{
temp[i] = &array[i]
}
delete [] array;
array = temp;
When I compile the code above, I get the error:
assigning to bankAccount * from incompatible type
bankAccount **; remove
Related
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.
I'm getting the error "undeclared identifier" on the commented line:
- (BOOL) isInIntArray:(NSInteger[])array theElem:(int)elem{
int i = 0;
NSInteger sizeOfArray = (sizeof array) / (sizeof array[0]);
while(i < sizeOfArray){
if(array[i] == elem){
return TRUE;
}
i++;
}
return FALSE;
}
- (int)getNextUnusedID{
int i = rand()%34;
while ([isInIntArray:idsUsed theElem:i]) { //here: Use of undeclared identifier 'isInIntArray'
i = rand()%34;
}
return i;
}
I really don't understand why, they are in the same .m file.
Why would that be?
Also, this code:
NSInteger sizeOfArray = (sizeof array) / (sizeof array[0]);
is giving me the warning:
Sizeof on array function will return Sizeof 'NSInteger *' (aka: 'int *') instead of 'NSInteger[]'"
How should I properly determine the size of an array?
It looks like you've missed out self from this line
while ([isInIntArray:idsUsed theElem:i])
This should be:
while ([self isInIntArray:idsUsed theElem:i])
As #CaptainRedmuff pointed out, you are missing the target object in method invocation, that is self.
//[object methodParam:x param:y];
[self isInIntArray:idsUsed theElem:i];
To your second Q. In C language you cannot determine the size of an array. That's why they are not used, since we have objects for this. I recommend you to use these:
NSMutableArray *array = [[NSMutableArray alloc] init]; // to create array
array[0] = #42; // to set value at index, `#` creates objects, in this case NSNumber
[array insertObject:#42 atindex:0]; // equivalent to the above
NSInteger integer = array[0].integerValue; // get the value, call integerMethod to get plain int
integer = [[array objectAtIndex:0] integerValue]; // equivalent to the above
[array containsObject:#42]; // test if given object is in the array
[array indexOfObject:#42]; // get index of object from array, NSNotFound if not found
array.count; // to get the number of objects
Important: These arrays have variable size and they are not limited! But you can access elements only at indexes 0..(n-1) (where n in number of objects) and you can set values only for indexes 0..n.
In other words, you can not do array[3] = #42; for empty array, you need to fill first 3 positions first (indexes 0, 1 and 2).
write this in .h file (declare the function)
- (BOOL) isInIntArray:(NSInteger[])array theElem:(int)elem;
and call the method using following way
while ([self isInIntArray:idsUsed theElem:i]) { //here: Use of undeclared identifier 'isInIntArray'
i = rand()%34;
}
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)
In my h file I declare a var that later should be an array:
#interface myClass : CCNode {
CGPoint *mVertices;
}
#end
In my init method:
mVertices = malloc(size * size * sizeof(CGPoint));
mVertices[0][0] = ccp(0,0);
At this last line I get an error Subscripted value is neither array nor pointer.
Why do I get this error and how to solve that problem?
mVertices is a pointer, but you treat it like a two-dimensional array which is not allowed (you may treat it like a one-dimensional array, though).
Creating a dynamic multi-dimensional array in (Objective)-C is tricky insofar as the compiler would need to know the size of all but the first dimension to actually compile where in memory the element is situated.
But you can do the calculation yourself:
mVertices[(row * size) + column] = ccp(row, column);
You might want to define a macro for that:
#define VERTICE_ACCESS(row,colum) mVertices[(row * size) + column]
Your array is not two dimensional. It's just a list of vertices.
If you want to allocate space for a dynamic two dimensional array in C you could do:
CGPoint** mVertices;
NSInteger nrows = 10;
NSInteger ncolumns = 5;
mVertices = calloc(sizeof(CGPoint*), nrows);
if(mVertices == NULL){NSLog(#"Not enough memory to allocate array.");}
for(NSUInteger i = 0; i < nrows; i++)
{
mVertices[i] = calloc(sizeof(CGPoint), ncolumns);
if(mVertices[i] == NULL){NSLog(#"Not enough memory to allocate array.");}
}
mVertices[0][5] = CGPointMake(12.0, 24.0);
mVertices[1][5] = CGPointMake(22.0, 24.0);
mVertices[2][5] = CGPointMake(32.0, 24.0);
mVertices[2][1] = CGPointMake(32.0, 24.0);
for(NSUInteger i = 0; i < nrows; i++)
{
for (int k = 0; k < ncolumns; k++)
{
NSLog(#"Point %#", NSStringFromPoint(NSPointFromCGPoint(mVertices[i][k])));
}
}
I used calloc instead of malloc to get CGPoints initialized with 0.0.
I have an array of pointers to Objective-C objects. These objects have a sort key associated with them. I'm trying to use qsort to sort the array of pointers to these objects. However, the first time my comparator is called, the first argument points to the first element in my array, but the second argument points to garbage, giving me an EXC_BAD_ACCESS when I try to access its sort key.
Here is my code (paraphrased):
- (void)foo:(int)numThingies {
Thingie **array;
array = malloc(sizeof(deck[0])*numThingies);
for(int i = 0; i < numThingies; i++) {
array[i] = [[Thingie alloc] initWithSortKey:(float)random()/RAND_MAX];
}
qsort(array[0], numThingies, sizeof(array[0]), thingieCmp);
}
int thingieCmp(const void *a, const void *b) {
const Thingie *ia = (const Thingie *)a;
const Thingie *ib = (const Thingie *)b;
if (ia.sortKey > ib.sortKey) return 1; //ib point to garbage, so ib.sortKey produces the EXC_BAD_ACCESS
else return -1;
}
Any ideas why this is happening?
The problem is two fold:
the first argument to qsort needs to be a pointer to the beginning of the array
the arguments passed to your sort function are actually pointers to the pointers of your data
Consider this working code:
int thingieCmp(const void *a, const void *b) {
NSObject *aO = *(NSObject **)a;
NSObject *bO = *(NSObject **)b;
if (aO.hash > bO.hash) return 1;
else return -1;
}
int main (int argc, const char * argv[]) {
NSObject **array;
array = malloc(sizeof(NSObject*)*20);
for(int i = 0; i < 20; i++) {
array[i] = [NSObject new];
}
qsort(array, 20, sizeof(NSObject*), thingieCmp);
return 0;
}
Note that the comparison function resolves the data pointers by NSObject *aO = *(NSObject **)a and the qsort function takes array as an argument directly.
All of this, though, begs the question of Why bother?
NSArray is very good at holding arrays of objects and is quite conveniently sortable. Performance is excellent in the general case. If performance analysis indicates that it isn't, you can optimize it away relatively easily.
Note, also, that I have been consistent in use of sizeof() -- same type in both places. Also, the const in your original code is not necessary.
I think, one mistake lies right in the line
qsort(array[0], numThingies, sizeof(array[0]), thingieCmp);
Try
qsort(&array[0], numThingies, sizeof(array[0]), thingieCmp);
or even
qsort(array, numThingies, sizeof(array[0]), thingieCmp);
instead. The compiler won't complain here, as qsort is supposed to take a void* and you pass it a Thingy* which can legally be cast to void* without warning, but you really want qsort to operate on the entire array, which has type Thingy**.
Another thing is: the comparator will be called with pointers to the array slots as arguments, so what you get is actually a Thingy**:
int
thingieCmp(void* a, void* b)
{
Thingie *ia = *((Thingie**)a);
Thingie *ib = *((Thingie**)b);
...
}