Put pointers into an array

[greathope123]

Hi,

I am playing pointer array but do not understand what is going on.

This pointer array *d[] looks correct:
int a1[2],b1[3];
int *d[]={a1,b1};
d[0][1]=1; d[1][2]=2;
cout<<d[0][1]<<", "<<d[1][2]<<endl;

Why this pointer array **d[] is not correct:
int a2[1][2],b2[3][4];
int **d[]={a2,b2};

I will be appreciated for any help!

 

[ArkM]

Let's consider the declaration:

int **d[] = ...

It's an array of pointers to pointer to int. In other words, an element of a is a pointer to pointer (to int).
However

int a1[1][2]

declares an array of arrays of two ints. In other words, it's possible to convert a1 to a pointer to an array (of 2 ints), but not in a pointer to pointer.

Analogous case

int b2[3][4]

declares an array of arrays of four ints. Have you noticed that both a2 and b2 (and elements of d) have different types?

So it's impossible to initialize d by different types values a2 and b2.

 

[greathope123]

Thank you.
I tried the same type:
int a[1][2];
int **b[1];
b[0]=a;
but still got error........

 

[ArkM]

Of course, you got exactly the same type error - reread my prev post again (and again. Reread your C text-book (arrays part)...

That's true type of array b:

int a[1][2]; // array of arrays of 2 ints
typedef int ArrayOf2ints[2];
ArrayOf2ints* b[1]; // compare with different type int** b[1]
b[0] = a; // that's OK