#include <iostream> using namespace std; int main() { int b[10]; int ( *a )[ 10 ]; // эта a = b; // error a[ 0 ] = new int; // error a = new int; // error }

I am trying to use the selection method to understand what it is and how it is used .

  • 6
    In such obscure cases, you can use such a service cdecl.org . He is good at telling. - KoVadim
  • Thank you, save yourself a bookmark - rikimaru2013

2 answers 2

To make it easier to understand the record

 int ( *a )[ 10 ];

you can enter an alias definition for the array

 typedef int T[10]; T *a;

that is, objects that a pointer can address are integer arrays of ten elements.

If you want, for example, that this pointer addresses such an array, you can write

 typedef int T[10]; T b; T *a; a = &b;

Then the expression *a or a[0] is an array b

For example, you can write

 typedef int T[10]; T b; T *a; a = &b; for ( int i = 0; i < 10; i++ ) a[0][i] = i;

If you want to dynamically allocate an array, then you should write

 typedef int T[10]; T *a; a = new T[1];

This is equivalent to the following code snippet.

 int ( *a )[10]; a = new int[1][10];

That is, such a pointer is usually used when working with two-dimensional arrays. For example,

 #include <iostream> int main() { const size_t M = 2; const size_t N = 10; int b[M][N] = { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }, { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 } }; for ( int ( *a )[N] = b; a != b + M; ++a ) { for ( int x : *a ) std::cout << x << ' '; std::cout << std::endl; } }

Console output

 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3 2 1 0
  • Possible without a pointer: for (auto&& row : b) for (auto x : row) cout << x << ' '; - jfs
  • @jfs I intentionally used a pointer. - Vlad from Moscow
  • I understand (this is the question of motivation: you can use the pointer, but not necessary). - jfs

Formally, this is a pointer to an array of 10 int .

So you need to assign as

 a = &b;

If you want to use to assign an element - then

 (*a)[0] = 12; // Присваивание b[0] = 12

If you mean an array of arrays of 10 elements,

 a[0][3] = 15; // Присваивание третьему элементу первого массива // по адресу a значение 15 - то же, что и b[3] = 15;

Well, and the last ... for example, like this:

 using arr = int[10]; a = new arr[1];
  • Thank you, tell me how it is used - because a static array is passed by reference and is not copied. When can a pointer come in handy? - rikimaru2013 February
  • Well, you can probably come up with ... but in C ++ it is generally much more convenient to use vector . Basically, here is a two-dimensional array :) We declare something like a = new arr[5] down in the answer, and we get a two-dimensional array ... - Harry