Explanation:
Dangling pointer:
If any pointer is pointing the memory address of any variable but after some variable has deleted from that memory location while pointer is still pointing such memory location. Such pointer is known as dangling pointer and this problem is known as dangling pointer problem.
Initially:
Later:
For example:
What will be output of following c program?
#include<stdio.h>
int *call();
int main(){
int *ptr;
ptr=call();
fflush(stdin);
printf("%d",*ptr);
return 0;
}
int * call(){
int x=25;
++x;
return &x;
}
Output: Garbage value
Note: In some compiler you may get warning message returning address of local variable or temporary
Explanation: variable x is local variable. Its scope and lifetime is within the function call hence after returning address of x variable x became dead and pointer is still pointing ptr is still pointing to that location.
Solution of this problem:
Make the variable x is as static variable. In other word we can say a pointer whose pointing object has been deleted is called dangling pointer.
#include<stdio.h>
int *call();
int main(){
int *ptr;
ptr=call();
fflush(stdin);
printf("%d",*ptr);
return 0;
}
int * call(){
static int x=25;
++x;
return &x;
}
Output: 26