Passing multi array in Objective C to a function

Question

I'm trying to pass a multi array (for example 3x3) to be printed in a matrice type form using Objective C. I'm fairly new to the language and am stuck. I can pass a single array, however with multi arrays I get the error Array type has incomplete element type.

void printMat(float value[][], int rows, int col)
{
    int j, k;
    float printpt;

    //Handles coloum printing
    for (k=0; k<col; k++)
    {
        NSLog(@"/n");
    //Handles row printing
    for (j=0; j<rows; j++)
    {
        printpt = value[j][k];
        NSLog(@"%f ", printpt);
    }
    }
}

I'm trying to call the function with

printMat(A, n, n)

Where A is the float A[30][30] and n=30. What the best way to achieve this or to pass multi dimensional arrays?

Alex Brown · Accepted Answer · 2010-11-19 16:51:09Z

2

pass it as float *value, then calculate the offset into the array appropriately. value[j*cols+k].

Note: data is held in the following order - first row (all), second row (all) etc)).

value[] is not incomplete because it behaves as value*.

However, value[][] is incomplete, because it has no way to understand the first [] array subscript without knowing the dimension of the second. For the same reason the statement value[j][k] makes no sense - without knowing the rowsize, how can you address the columns?

float value[][30] works fine, but won't help you because you want to supply a variable size.

edited Nov 19, 2010 at 16:51

answered Nov 19, 2010 at 16:34

Alex Brown

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1 Comment

taskinoor Over a year ago

'float value **' or 'float **value'?

ennuikiller · Accepted Answer · 2010-11-19 16:38:15Z

1

well for one thing this is not objective-C (with the exception of the NSLog statements) .... in objective-c you would simply create the arrays like so:

NSArray *row1 = [NSArray  arrayWithObjects:obj1,obj2,obj3,nil];
NSArray *row2 = [NSArray  arrayWithObjects:obj3,obj4,obj5,nil];

NSArray *matrix  = [NSArray arrayWithPjects:row1,row2,nil];

and then you function prototype would simply be:

-(void) printMat:(NSArray *)matrix;

answered Nov 19, 2010 at 16:38

ennuikiller

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2 Comments

taskinoor Over a year ago

arrayWithPjects? I guess thats a typo.

Cam Over a year ago

The main reason I avoided NSArray was due to being application requiring up to 40x40 matrices (signal processing).

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