C Language Review 3/24

1. One-dimensional arrays and pointers

int a[]; int *p = A;

A[i] <=>* (a+i) <=>* (p+i)

A as the array name of a one-dimensional array, its value is fixed. When the array name is used as a function parameter, the shape parameter group name is handled as a pointer variable. If you use a pointer variable as an argument, you must first make the pointer variable have a certain value, pointing to a defined object.

2. Two-d arrays and pointers

Define a two-dimensional array int a[3][4];

From a two-dimensional array perspective, a represents the address of the first element of a two-dimensional array, and now the first element is no longer a simple integer element, but a one-dimensional array consisting of 4 integral elements, so a represents the first address of the first row, and A + 1 represents the first address of the line with the ordinal 1. If the first row address of the two-dimensional array is 2000 and an integer data is 4 bytes, the value of a + 1 should be 2000 + 4*4 = 2016. A[0],A[1],A[2] Since it is a one-dimensional array name, and the C language specifies that the array name represents the address of the first element of the array, A[0] represents the address of the No. 0 column element in the one-dimensional array a[0], or &a[0][0]. a[i][j]=* (A[i] + j) =* (* (A + i) + j). If A is a one-dimensional array name, then A[i] represents the storage unit of an element of the array ordinal of I. A[i] is a physical address, which is the storage unit. But if a is a two-dimensional array, then a[i] is a one-dimensional array name, which is just an address and does not represent the value of an element (such as the same-dimensional array name is just a pointer constant). The values for a + 1 and * (A + 1) are 2016, but the meaning is different, A + 1 is the 1 header address, * (A + 1) equivalent to A[1], which represents the address of the 1 row 0 column element a[1][0].

A two-dimensional array name is a pointer to a row, and a one-dimensional array name is a pointer to a column. The pointer to the column is converted to a pointer to the row, preceded by A *. For example, a and a + 1 are pointers to rows, preceded by A * is *a and * (a+1), they become pointers to columns, pointing to an array of 0 rows 0 column elements and 1 rows 0 columns of elements. Conversely, the pointer to the column is preceded by a &, which becomes a pointer to the row. For example, A[0] is a pointer to a 0-row 0-column element, preceded by A & as &a[0], because a[0] is equivalent to * (a+0), so &a[0] is equivalent to &*a, which is equivalent to a, which points to 0 rows of a two-dimensional array. Do not take &a[i] as the physical address of the a[i] element, because there is no real data storage unit such as A[i]. It is just a method of calculating the address, which can get the first address of line I, the values of &a[i] and a[i] are the same, but their meanings are different. &a[i] or a+i points to the row, A[i] or * (A + i) to the column.

inta[3][4] = { {1,2,3,4},{1,2,3,4},{1,3,4,4} };int(*p) [4];//defines p as a pointer variable pointing to a one-dimensional array containing 4 integral elementsp =a;printf ("%d", * (* (P +1) +2));

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C Language Review 3/24