c++ - Variable changes value unexpectedly -


i have code supposed store data in in 2 block array.

here code :

#include <iostream> #define position_data 1 #define x_axis 1 #define y_axis 0  using namespace std;  typedef int dot_coordinates[position_data];  void set_coordinates(dot_coordinates* dot,int x, int y);   int main() { dot_coordinates dot1,dot2,dot3,dot4;  set_coordinates(&dot1,0,0); set_coordinates(&dot2,7,0); set_coordinates(&dot3,0,7); set_coordinates(&dot4,7,7);  printf("\np1 : x=%d y=%d\n",dot1[x_axis],dot1[y_axis]); printf("\np2 : x=%d y=%d\n",dot2[x_axis],dot2[y_axis]); printf("\np3 : x=%d y=%d\n",dot3[x_axis],dot3[y_axis]); printf("\np4 : x=%d y=%d\n",dot4[x_axis],dot4[y_axis]);      return 0; }  void set_coordinates(dot_coordinates* dot,int x, int y) { *dot[x_axis] = x; *dot[y_axis] = y; }

the console result following :

p1 : x=0 y=7

p2 : x=7 y=0

p3 : x=0 y=7

p4 : x=7 y=7

shouldn't y=7 y=0 p1 ?

now here happens when replace lines

set_coordinates(&dot1,0,0); set_coordinates(&dot2,7,0); set_coordinates(&dot3,0,7); set_coordinates(&dot4,7,7);

with (the rest of code same)

set_coordinates(&dot2,7,0); set_coordinates(&dot3,0,7); set_coordinates(&dot4,7,7); set_coordinates(&dot1,0,0);

the result here :

p1 : x=0 y=0

p2 : x=0 y=0

p3 : x=0 y=7

p4 : x=7 y=7

i have been trying understand why happening couldn't figure out why p1[x_axis] copying p2[y_axis]. appreciated !

you've defined type 'dot_coordinates' array of length 1 (via position_data macro). then, in set_coordinates function, index second element. undefined behavior, , in particular circumstance, overwriting variables stored in adjacent stack space.


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