Pointer and array & pointer and const & struct and Const

Pointers and arrays ：

        Pointer can access array subscript

         for example ：

        void Show(int* p, int length)// Output function

        {

              for (int i = 0; i < length; i++)

                   printf("%d", p[i]);// perhaps printf("%d", *(p+i));p[i] Equivalent to *(p+i)

        }

        int main()

        {

             int arr[] = { 1,2,3,4 };

             Show(arr, sizeof(arr) / sizeof(arr[0]));

        }

The pointer and const:

const Used to decorate functions and variables

const Modify the constant ：

        const int a=10;//a Is a constant variable , Do not modify the

const int * And int* const：

        const int *p=&a; // allow p Point to a, But it's not modifiable a,p Can point to anything .a Is a constant , No modification allowed .

        int* const p=&a; // here ,const modification p Variable ,p Can only point to a, You can also modify a（ At present only if a It's a variable. ）, however p It is not allowed to point to .

（ Memory can be understood in this way , Only remember which cannot change ：const int *p=&a,const And then int *p, because *p=a, therefore a The value of does not change  ;int* const p=&a,const And then p, modification p,p The contents of the grid are a The address of ,p By const, So the grid doesn't change ,p The direction of .

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const The wrong use of ：

        （1）const int a=10;

                 int* p=&a;// because p No modification allowed a, So the compiler warns

        （2）const int *p=&a;// limit P Don't modify a

                 *p=&b;

          (3)const int a=10;

              int *const p=&a;// Will report a mistake , This means p You can modify a Value , however a It's a constant variable again

const char* name and char name[10] The difference between ：

        1. In memory ： Pointer occupied 4 Bytes , The memory of the array may be large

        2. Want to change the character , It must be an array .

Structure and const:

There is a point of understanding to emphasize ：

        eg:

        struct Student

        {

                const char* name;

                 int age;

                char sex;

        };

        int main()

        {

        struct Student s1 = { " Li Si ",14," male "};

        }

explain ： Define in the structure const char* name, You can't change the name , Correct usage .

But if const Embellish gender , Can be s1.sex=‘ Woman ’ Change direction .“ male ” It is amended as follows “ Woman ”, But you can't “ male ” It is amended as follows “ men ”, It means Not to change the original character , Instead, it changes the direction of the variable .