Pointer concept & character pointer & pointer array yyds dry inventory

1. The concept of pointer

1. A pointer is a variable , It's used to store the address , The address uniquely identifies a piece of memory space

2. The size of the pointer variable is fixed as 4/8 Bytes (32/64 Bit platform )

3. Pointers are typed , The type of pointer determines the pointer ± Integer step size , Pointer dereference permission

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2. Character pointer

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 situation 1：char a = 'a'; char* p = &a;
 situation 2：char* p = "Mango";

     

      
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int main()
{
    char ch = 'w';
    char* pc = &ch;//pc It points to a character constant 
    char* p = "hello";	//hello Is a constant string , p Save the address of the first character of the constant string 
   // *p = 'w';//err, The constant string is stored in the constant area , The content cannot be modified 
    return 0;
}

     

      
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Because constant strings cannot be modified , So you can use const Better decoration , When compiling like this , If someone changes , Just report the mistake directly

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Exercises

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 int main()
 {
     char str1[] = "hello bit";
     char str2[] = "hello bit";
     const char* str3 = "hello bit";
     const char* str4 = "hello bit";
     if(str1 == str2)
     {
         printf("str1 and str2 are same\n");
     }
     else
     {
          printf("str1 and str2 are not same\n");
     }
     if(str3 == str4)
     {
         printf("str3 and str4 are same\n");
     }
     else
     {
         printf("str3 and str4 are not same");
     }
     return 0;
 }

     

      
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Print structure

str1 and str2 are not same
str3 and str4 are same

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reason ：

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str1 and str2 It's a different array , Open up space in the stack area .
str3 and str4 Points to the same constant string , Both save the first character address of the constant string 
    
 here str3 and str4 Points to the same constant string .
  C/C++ The constant string is stored in a separate memory area , When a few pointers . When pointing to the same string , They actually point to the same block of memory . However, when initializing different arrays with the same constant string, different memory blocks will be opened up . therefore str1 and str2 Different ,str3 and str4 Different .

     

      
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3. Pointer array - It's an array

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int arr[10];// integer array - An array of shapes 
char arr[10];// A character array - An array of characters 
char* arr[5]//arr Is an array of character pointers 
int* arr[5];//arr Is an array of integer pointers 

     

      
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int main()
{
    int a = 10;
    int b = 20;
    int c = 30;
    int d = 40;
    int* arr[4] = {&a,&b,&c,&d};	//arr2 Is to shape the pointer array 
    for(int i = 0;i<4;i++)
    {
        //printf("%d ",*(arr+i));//err
        //*(arr+i): Array i The content of the subscript , The printed address is 
        printf("%d ", *(*(arr + i)));
    }
}

     

      
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Pointer array stores the array name of integer array

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int main()
{
    int arr1[]={1,2,3,4,5};
    int arr2[]={2,3,4,5,6};
    int arr3[]={3,4,5,6,7};
    int* parr[]={arr1,arr2,arr3};
    // The array name is the first element address , yes int* type 
    // So use int*  The array of , It's like a two-dimensional array 
    int i= 0;
    int j =0;
    for(i = 0;i<3;i++)
    {
        for(j = 0;j<5;j++)
        {
            printf("%d ",parr[i][j]);
        }
        printf("\n");
    }
}

     

      
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It's like a two-dimensional array ,

parr[i] : Get the subscript i The starting address of the array , Equivalent to getting the array name ,

parr[i][j]: Get the subscript i The subscript in the array of is j The elements of

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