1. The relationship between arrays and pointers
3. How to use pointers to represent arrays:
Preface
The author learned a little bit of C language when he was a freshman, but it has never been used since then. Recently, I have used it and found that there are many things I don't know, so I started a blog to record the learning process.
1. The relationship between arrays and pointers
C language supports the data structure of array, which is a collection of fixed-size elements of the same type.
To declare an array, you need to specify the type and number of elements. As follows:
//type arrayName [arraySize],声明一个int类型、包含10个元素的数组
int p[10];Now p is a usable array that can hold 10 int type data. p[0] represents the first element in it
The array name, which is p here , is a pointer to the first element in the array . That is, the value of p is the address of the first element in the array p.
2. Pointers in C
Each variable has a memory location, and the address can be accessed using the & operator.
What is a pointer? A pointer is a variable used to store a memory address (there are also constant pointers). It is just like other variables or constants, except that it stores the address value, as shown below.
int a = 10;
int *p = &a;The value of a pointer is an address , but it can also represent the value pointed to by the address. For example, the value of p here is the address of a , and *p can represent the value pointed to by this address, which is 10.
int a = 10;
int *p = &a;
printf("a的地址为%p\n",p);
printf("a的值为%d\n",*p);
How to define pointers?
The general form of pointer variable declaration is
//type *var_name
int *ip; //一个整型的指针，也就是ip指向的是整型量
doubel *dp; //一个double 型的指针
float *fp; //一个浮点型的指针Note that the type here is the type of the amount pointed to by the pointer . For example, ip is the address of an integer data, but the value type of the pointer itself is the same, which is a long hexadecimal number representing the address.
3. How to use pointers to represent arrays:
As mentioned in the first part, the array name is actually a pointer to the first element in the array, that is, the array name can be used as a constant pointer (the two are not completely equivalent).
Regarding what are constant pointers and pointer constants:
Constant pointer : The starting point is the pointer. This is a pointer, but it is a constant pointer, that is, it points to a constant. (The pointer itself can be a variable). As shown in the following example.
const int *p = &a;
Here p is a pointer variable (can be assigned again), pointing to the constant a.
Pointer constant : The starting point is a constant, indicating that it is a constant of pointer type. As shown in the following example:
int *const p = &a;//定义一个指针常量Here p is a constant, its value is the address of a, and p cannot be assigned again.
How to use pointers to represent arrays?
For example, an array bear is declared here. The bear below is a pointer to bear[0], that is, bear is equivalent to a constant pointer, and the address of bear[0] is stored.
int bear[2];We know that bear is equivalent to a pointer type quantity, so bear can be assigned to the pointer here. Now you can use var_bear to access the array. For example, *(var_bear) points to bear[0], *(var_bear+1) points to bear[1];
By the way, var_bear+1 actually adds 4 to its value. This is because the int type occupies 4 bytes.
Summarize
Pointer variables store address values, and array names can be regarded as constant pointers.