http://www.neilstuff.com/guide_to_cpp/notes/Multi%20Dimension%20Arrays%20and%20Pointer%20Pointers.htm
According to this site, I should be able to use the following c
Your assigned is flawed. p_stuff;
is pointer to pointer to double
whereas stuff
is two dimensional array( array of arrays)
A single dimension array decays to the pointer to its first element. A 2 dimensional array decays to pointer to a single dimension array.
Try this
double stuff[3][3];
double (*p_stuff)[3]; // pointer to array of 3 int
p_stuff = stuff;
double ** p_stuff;
corresponds to an array of pointer to double. double stuff[3][3]
doesn't have any pointers - it's a 2D array of double.
Below is maybe your answer:
#include <stdio.h>
#include <stdlib.h>
typedef unsigned int uint;
uint m[10][20];
uint **ppm;
int main() {
int i;
ppm = (uint **)m;
for (i =0; i<10; ++i)ppm[i] = (uint *)&m[i];
m[1][1] = 10;
printf("0x%x vs 0x%x: %d vs %d\n", ppm,m, m[1][1], *(*(ppm+1)+1));
return 0;
}
The result's on console screen:
0x6010a0 vs 0x6010a0: 10 vs 10
Regarding the edit: to pass this double stuff[3][3]
to a C function, you could
1) pass a pointer to the whole 2D array:
void dostuff(double (*a)[3][3])
{
// access them as (*a)[0][0] .. (*a)[2][2]
}
int main()
{
double stuff[3][3];
double (*p_stuff)[3][3] = &stuff;
dostuff(p_stuff);
}
2) pass a pointer to the first 1D array (first row) and the number of rows
void dostuff(double a[][3], int rows)
{
// access them as a[0][0] .. a[2][2]
}
int main()
{
double stuff[3][3];
double (*p_stuff)[3] = stuff;
dostuff(p_stuff, 3);
}
3) pass a pointer to the first value in the first row and the number of both columns and rows
void dostuff(double a[], int rows, int cols)
{
// access them as a[0] .. a[8];
}
int main()
{
double stuff[3][3];
double *p_stuff = stuff[0];
dostuff(p_stuff, 3, 3);
}
(that this last option is not strictly standards-compliant since it advances a pointer to an element of a 1D array (the first row) past the end of that array)
If that wasn't a C function, there'd be a few more options!
In addition to Cubbi's detailed answer, the following way is just natural to pass a 2-dim array to a function:
void dostuff(void *a1, int rows, int cols)
{
double (*a)[cols] = (double (*)[cols]) a1;
// access them as a[0][0] .. a[rows-1][cols-1];
}
int main()
{
double stuff[3][3];
dostuff(stuff, 3, 3);
}
You don't have to cast them in advance since the newest C++ (C++14) supports run-time sized arrays.