How to new a two-dimension array of int

[Larry Lindsey]

For compiler g++ on Linux, it doesn't work if I use

int **data = new int[m][n];

Can I new an array of int* first, and new an one-dimension array for the
first int*,
then use a loop to make every int* point to the right position?

int **data = new int*[m];
data[0] = new int[m*n];
for(i = 1; i < m; i++)
data = data[0] + i * n;

It should works, however, it failed in my MPI program.
Could anyone give me a better method? Thanks.

Use pointers. C++ requires you to instantiate arrays with const values. So
instead:
int **data = (int**)malloc(m*sizeof(int*));
for (i=0;i<m;i++)
(*data+i)=(int*)malloc(n*sizeof(int));

That would be my take. This will work, but there will probably be better
ways of doing it.

--Larry

 

[Wonder]

For compiler g++ on Linux, it doesn't work if I use

int **data = new int[m][n];

Can I new an array of int* first, and new an one-dimension array for the
first int*,
then use a loop to make every int* point to the right position?

int **data = new int*[m];
data[0] = new int[m*n];
for(i = 1; i < m; i++)
data = data[0] + i * n;

It should works, however, it failed in my MPI program.
Could anyone give me a better method? Thanks.

 

[Ron Natalie]

For compiler g++ on Linux, it doesn't work if I use

int **data = new int[m][n];

Because the type of new int[m][n] is not int**.
POINTERS ARE NOT THE SAME AS ARRAYS.

Can I new an array of int* first, and new an one-dimension array for the
first int*,
then use a loop to make every int* point to the right position?

int **data = new int*[m];
data[0] = new int[m*n];
for(i = 1; i < m; i++)
data = data[0] + i * n;

This looks like it should have worked to me. What happened?

 

[Ron Natalie]

Use pointers. C++ requires you to instantiate arrays with const values. So
instead:

He did use pointers. Why on earth are you using malloc? Your code won't
work anyhow. Presuably you meant *(data+i) or data in the lhs of the
last line.

 

[Larry Lindsey]

Use pointers. C++ requires you to instantiate arrays with const values. So
instead:

He did use pointers. Why on earth are you using malloc? Your code won't
work anyhow. Presuably you meant *(data+i) or data in the lhs of the
last line.

Oh, yeah. Good point. I'm basically a newbie anywho.

 

[Mike Wahler]

Oh, yeah. Good point.
I'm basically a newbie anywho.

So why do you purport to teach others?

-Mike