c.txt

UNDERSTANDING STRUCTS
---------------------

Previously i thought that the were equivalent. ie. I thought an array was just a pointer to the first element.

struct HooStruct1 {
    UInt32 mNumberOfFloats;
    CGFloat arggg[1024];
};

struct HooStruct2 {
    UInt32 mNumberOfFloats;
    CGFloat *arggg;
};

I was wrong. HooStruct1 allocates the memory as well

NSUInteger test1 = sizeof(struct HooStruc1); // == 4100
NSUInteger test2 = sizeof(struct HooStruc2); // == 8


Sooo, you can use this to define a variable size array. Like so..

struct HooStruct3 {
    UInt32 mNumberOfFloats;
    CGFloat arggg[1]; // This is key.. must come last in struct. Size of 1, then when we malloc we can multiply it by the quantity we want
};

int arraySize = 50;
struct HooStruct3 *arrayOf50;
arrayOf50 = malloc( sizeof *arrayOf50 + (arraySize - 1) * sizeof arrayOf50->arggg[0] );
arrayOf50->mNumberOfFloats = arraySize;
...
free( arrayOf50 );


** -- **

char (*j)[20]; // j is a pointer to an array of 20 char
j = (char(*)[20])malloc(20);

const int * grape;				// object is readonly
int const * grape;				// object is readonly
int * const grape_jelly;		// pointer is readonly
const int * const grape_jam;	// object and pointer readonly
int const * const grape_jam;	// object and pointer readonly