I am trying to print a 2D matrix with using [], instead I want to use * like a pointer.
So with a 1 D array I'd do: *(arr+i) for example.
What's the syntax used to replace in matrix[][] ?
Here's the code:
for (i = 0; i < size; i++)
{
for (j = 0; j < (size * 2); j++)
{
printf(" %5d", matrix[i][j]);
}
printf("\n");
}
P.S, I did try several things like:
*(matrix+i+j);
*(matrix+i)+*(matrix+j);
Of course none of that worked.
Thank you for your help and time!
Use the * two times. Each of * will basically replace one []:
*(*(matrix+i)+j)
matrix with type int[][] decays to pointer &matrix[0] with type int(*)[] (I hope I wrote that right) before +i is performed.int x[3][5]; with sentence: "...In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to a pointer to the initial array of five ints. ..."You can try this-
*(*(matrix+i)+j) //reduce level of indirection by using *
This may depend on how matrix was allocated or passed to a function.
int A[10][15];
This uses a contiguous block of memory. To address the elements without using array notation use:
A +(i*15)+j // user694733 showed this is wrong
((int *)A)+(i*15)+j // this is horribly ugly but is correct
Note the 15, as each row consists of 15 elements. Better solutions are presented in other answers here.
In the following:
int *A[10];
A is an array of 10 pointers to ints. Assuming each array element has been allocated using malloc, you address the elements without using array notation as:
*(A+i) + j;
that is, you take A, then take the ith element, dereference that and add j as the second index.
--EDIT--
And to be complete:
int foo(int *p)
here a function just receives a pointer to zero or more ints. The pointer points to a contiguous, linear block of memory into which you can place an n-dimensional array. How many dimensions there are and the upper bound of each dimension the function can only know through parameters or global variables.
To address the cells of the n-dimensional array, the programmer must calculate the addresses him/herself, using the above notation.
int foo3(int *m, int dim2, int dim3, int i, int j, int k)
{
int *cell = m + i*dim3*dim2 + j*dim2 + k;
return *cell;
}
A+(i*15)+j is error prone and unnecessary. It's only needed if you allocate 2D as 1D array.
int A[10][15] are contiguous in memory. That has nothing to do with "allocating a 2D as 1D array." I can treat any contiguous block of memory as an n-dimensional array. It is just to show the OP how to do it. It is not nice, but that's what he wants to learn.*(*(matrix+i)+j) does it without needing to specify the size explicitly.A+(i*N)+j calculation.int m[2][2]; accessing last element m[1][1] using syntax m+(i*size)+j, now m+(1*2)+1, will expand to (char*)&m[0] + sizeof(int[2]) * ((1*2)+1), which is out of array bounds. Example on Ideone.
T[][]orT**?