I realize theres a lot of array and pointer questions, but I had one thats extremely specific... Its actually from a test I took in class awhile ago and I'm still having trouble with it.
The question is - Write out a complete declaration for
A variable named pmatrix that is a pointer to an array of 8 arrays of 10 pointers to integers
so far I'm thinking something like
int*pmatrix[8][10] ,
more concerned with a good explanation than just an answer.
thanks!
A variable named pmatrix that is a pointer:
*pmatrix
to an array of 8
(*pmatrix)[8]
arrays of 10
(*pmatrix)[8][10]
pointers to integers:
int *(*pmatrix)[8][10]
Substituting into cdecl, we are told the following:
declare pmatrix as pointer to array 8 of array 10 of pointer to int
which is where we started!
int*pmatrix[8][10]
There's an issue of precedence: [] has a higher precedence
than '*', so that is an array[8] of array[10] of pointer to
int. You need to add parentheses to override the precedence:
int (*pmatrix)[8][10]
(More parentheses are possible. I'm not sure that
int (((*pmatrix)[8])[10]);
would be an improvement, however:-).)
int, not just int.
The answer to your question would be
int* (*pmatrix)[8][10];
Remember though, arrays are just pointers to the first element of the array, so an array is a pointer and a pointer is an array (sometimes of just one element).
Note though, that beneath this array is really just a single-dimensional array of 80 elements. If you do an index like this:
int pmatrix[8][10];
pmatrix[3][5];
The compiler treats that as if you did:
*(pmatrix + (3 * 10) + 5);
because the index [3][5] accesses the 5th element (+ 5) of the 3rd subarray (3 * 10 (10 being the size of each sub array)).
int *pmatrix[8][10] is the right answer. It's not the right answer. The right answer is int *(*pmatrix)[8][10].a (in int a[5]) is no more a pointer than b is in int b;.int a[5], and that the result of new (and malloc) is simply a pointer to "allocated space".int** pmatrix = new int*[8]; // Array of 8 pointers to arrays
for(int i = 0; i < 8; ++i) pmatrix[i] = new int[10]; // Create each array
