34th lesson multidimensional arrays and multidimensional pointers

1. pointers pointing to pointers

(1) The nature of the pointer is a variable that takes up a certain amount of memory space

(2) pointer can be defined to hold the address value of the pointer variable

(3) The pointer is a variable, and there is also a value call and a call to the address

"Instance analysis" traversing a two-dimensional array

2. Array name

(1) One-dimensional array name represents the address of the first element of the array: int a[5];a is of type int*

(2) The two-dimensional array name also represents the address of the first element of the array: an int (*) a[3][5],a is of type int (*) [5].

		Fetch address (&)	sizeof
array name: A	① two-dimensional array name a point to address of the first element of the array , which is the address of line 1th (A[0]) (note, not the address of a[0][0]). Therefore, A is called the row pointer , which points to the address of the 1th row element (one-dimensional array). The type of this element is Int (*) [5] (that is, a one-dimensional array). So the type of a is int (*) [5];a can be treated as a row pointer, ②a + 1 is a pointer to the second row, A + I represents a pointer to the line i + 1 (also int (*) [5] type) ...	① &a represents the address of the entire two-dimensional array , so &a + 1 points to the back of the last element of the two-dimensional array.  ,	①sizeof (a) represents the size of the entire two-dimensional array. ②sizeof (&a) is a pointer size of 4 bytes. ③sizeof (*&a) equals sizeof (a)
a[i]	①a[i] Type: If you think of a two-dimensional array as an array of three elements (one-dimensional arrays), then these three the a[0], a[1], a[2] , respectively. Thus, a[0] can be thought of as the address of the first element (A[0][0]) to line 1th (one-dimensional array), A[i] is the address of the first element of line I + 1 (one-dimensional array), so A[i] is a type int* . ②a[i] + 1 represents the address of the 2nd element of this row of arrays, i.e. A[i] + 1 is the address of the a[i][1] element, * (A[i] + 1) is the value of the a[i][1] element. Similarly, A[i] + j is the address that points to a[i][j], * (A[i] + j) is the value of a[i][j].	&a[i] The represents the line I + 1 line address of the entire one-dimensional array . Therefore, &a[i] + 1 is a pointer to the next line of this row array.	①sizeof (A[i]): A[i] is a one-dimensional array. sizeof (A[i]) is the size of this array. ②sizeof (&a[i]) is a pointer size of 4 bytes. ③sizeof (*&a[i]) equals sizeof (A[i])
a[i][j]	int .	&a[i][j] represents this , that is, int*	①sizeof (A[i][j]): A[i][j] Represents the type of the element. ②sizeof (&a[i][j]) is the pointer size. ③sizeof (*&a[i][j]) equals sizeof (A[i][j])
Note	① Typically, the array name can be thought of as the address of the first element, whereas the type of the array name A, a[i] in the table refers to the type when they represent the first element of the respective array. ② but when an array name is taken to the address character (&) or sizeof, it cannot be considered as the address of the first element, but rather as the whole . Please note the analysis of the & and sizeof two columns in the table.

Information for the "Instance Analysis" array

#include <stdio.h>intMainintargcChar* argv[],Char*env[]) {        inta[3][5] = {0}; intC; printf ("Information for array:a[3][5]:\n"); printf ("a = 0x%08X, a + 1 = 0x%08X, sizeof (a) =%d\n", A, A +1,sizeof(a)); printf ("&a = 0x%08X, &a + 1 = 0x%08X, sizeof (&a) =%d, sizeof (*&a) =%d\n",               &a, &a +1,sizeof(&a),sizeof(*&a)); printf ("\ n");
A[i] points to the first element of a one-dimensional array,a[i]+1 points to the 2nd element of the row . sizeof (A[i]) cannot be considered as the first element , but the entire one-dimensional array of this line for(c=0;c<5; C + +) {printf ("a[%d] = 0x%08X, a[%d] + 1 = 0x%08X, sizeof (a[%d]) =%d,\n", C, A[c], C, A[c]+1. cnsizeof(A[c])); } printf ("\ n");
//A[i] cannot be regarded as the first element of this line , but rather as an entire one-dimensional array when the a[i is taken for the & address character. That is &a[i] represents the entire array of i+1
    &a[i]+1 represents the next line.

 for(c=0;c<5; C + +) {printf ("&a[%d] = 0x%08X, &a[%d] + 1 = 0x%08X, sizeof (&a[%d]) =%d, sizeof (*&a[%d]) =%d\n", C,&a[c],c, &a[c] +1. cnsizeof(&a[c]), C,sizeof(*&a[c])); }    return 0;}/* output result: Information for array:a[3][5]:a = 0x0023fe80, a + 1 = 0x0023fe94, sizeof (a) = 60&a = 0x0023fe80, &a + 1 = 0x0023febc, sizeof (&A) = 4, sizeof (*&A) = 60a[0] = 0x0023fe80, a[0] + 1 = 0x0023fe84, S Izeof (a[0]) = 20,a[1] = 0x0023fe94, a[1] + 1 = 0x0023fe98, sizeof (a[1]) = 20,a[2] = 0x0023fea8, a[2] + 1 = 0x0023feac, siz EOF (a[2]) = 20,a[3] = 0X0023FEBC, a[3] + 1 = 0x0023fec0, sizeof (a[3]) = 20,a[4] = 0x0023fed0, a[4] + 1 = 0x0023fed4, Sizeo  F (a[4]) = 20,&a[0] = 0x0023fe80, &a[0] + 1 = 0x0023fe94, sizeof (&a[0]) = 4, sizeof (*&a[0]) = 20&a[1] =  0x0023fe94, &a[1] + 1 = 0x0023fea8, sizeof (&a[1]) = 4, sizeof (*&a[1]) = 20&a[2] = 0x0023fea8, &a[2] + 1 = 0x0023febc, sizeof (&a[2]) = 4, sizeof (*&a[2]) = 20&a[3] = 0X0023FEBC, &a[3] + 1 = 0x0023fed0, sizeof ( &A[3]) = 4, sizeof (*&a[3]) = 20&a[4] = 0x0023fed0, &a[4] + 1 = 0x0023fee4, sizeof (&a[4]) = 4, sizeof (* &A[4]) = */

34th lesson multidimensional arrays and multidimensional pointers