how make pointers to follow another pointer in c-CodePudding

I want to write a program that uses Pointers and when I change the value of a pointer, the others follow that pointer; here is my code:

int * M1  =   new  int(1) ;
int * M2  =   new  int(2) ;
int * M3  =   new  int(3) ;
int * M4  =   new  int(4) ;
int * M5  =   new  int(5) ;

int * M6  =   new  int(6) ;
int * M7  =   new  int(7) ;
int * M8  =   new  int(8) ;
int * M9  =   new  int(9)  ;
int * M10  =  new  int(10) ;





M1 = M2  = M3  = M4  = M5;

M6 = M7  = M8  = M9  = M10;



*M5  = *M10;  //  now *M1 : *M5   is equal  *M10

*M10   = 120; //  this only changes  *M6  : *M10   but I want *M1 : *M5  changes too

how can I change whole *M1 : *M10 without using loop??

CodePudding user response：

I don't think you can do what you're asking in the way you're asking it. Pointers are kind of like labels for memory locations, and moving one label doesn't change the location any of the other labels are pointing to. Let's visualize the starting state:

1 <- M1
2 <- M2
3 <- M3
4 <- M4
5 <- M5
6 <- M6
7 <- M7
8 <- M8
9 <- M9
10 <- M10

On the M1 = M2 = M3 = M4 = M5 line, you're moving the first four pointers (just labels) to point where M5 is pointing at (call it location 5). Similarly for the next line, to point M6:M9 to where M10 is pointing at (call it location 10).

1 <- 
2 <- 
3 <- 
4 <- 
5 <- M1,M2,M3,M4,M5
6 <- 
7 <- 
8 <- 
9 <- 
10 <- M6,M7,M8,M9,M10

With your line *M5 = *M10, you change just the value at M5's location, location 5. The location of all the labels doesn't change.

1 <- 
2 <- 
3 <- 
4 <- 
10 <- M1,M2,M3,M4,M5
6 <- 
7 <- 
8 <- 
9 <- 
10 <- M6,M7,M8,M9,M10

Your last line does the same, for location 10:

1 <- 
2 <- 
3 <- 
4 <- 
10 <- M1,M2,M3,M4,M5
6 <- 
7 <- 
8 <- 
9 <- 
120 <- M6,M7,M8,M9,M10

If you want to move those labels again, you'll need to move them individually. They point to a location, but are each their own separate labels. The shortest way to do what you want from the end of your program is:

M1 = M2 = M3 = M4 = M5 = M10;

1 <- 
2 <- 
3 <- 
4 <- 
10 <-
6 <- 
7 <- 
8 <- 
9 <- 
120 <- M1,M2,M3,M4,M5,M6,M7,M8,M9,M10

If you want all of them to point at that last location by pointing them to M5's location, you can do that by modifying your code a little bit to move M5 first:

int * M1  =   new  int(1) ;
int * M2  =   new  int(2) ;
int * M3  =   new  int(3) ;
int * M4  =   new  int(4) ;
int * M5  =   new  int(5) ;

int * M6  =   new  int(6) ;
int * M7  =   new  int(7) ;
int * M8  =   new  int(8) ;
int * M9  =   new  int(9)  ;
int * M10  =  new  int(10) ;


M5 = M10; // M5 now points to location 10


M1 = M2  = M3  = M4  = M5; // M1:M4 now point to location 10

M6 = M7  = M8  = M9  = M10; // M6:M9 now point to location 10


*M5  = *M10;  //  This does nothing, since they already point to the same location

*M10   = 120; //  All values point to location 10, which now holds the value 120

The resulting diagram here is:

1 <-
2 <-
3 <-
4 <-
5 <-
6 <-
7 <-
8 <-
9 <-
120 <- M1,M2,M3,M4,M5,M6,M7,M8,M9,M10