c - change of one pointer affect other pointer -

c - change of one pointer affect other pointer -

how possible komv->next become null on code before end of while loop? notice become null after line town->previous->next=town->next cant understand why happened. programme terminated segmentation fault.

komv=list->first; while ((komv->next)!=null) { if(town->num>=komv->next->num) { town->previous->next=town->next; if(town->next!=null) town->next->previous=town->previous; town->next=komv->next; town->previous=komv; komv->next->previous=town; // gdb komv->next=null komv->next=town; break; } komv=komv->next; }

if komv node preceding town in list, town->previous == komv. if town lastly node town->next == null. when true @ same time, this:

town->previous->next=town->next;

reduces to:

komv->next = null;

in case, looks there no need modify list, prepare problem modifying status to

if ((town != komv->next) && (town->num >= komv->next->num)) {

there might improve solution, too, depending on assumptions , behavior want. example, if acceptable insert town after nodes having same num instead of before, utilize condition:

if (town->num > komv->next->num) {

c pointers struct