A dangling pointer points to memory that has already been freed. The storage is no longer allocated. Trying to access it might cause a Segmentation fault.
Common way to end up with a dangling pointer:
char *func()
{
char str[10];
strcpy(str, "Hello!");
return str;
}
//returned pointer points to str which has gone out of scope.
You are returning an address which was a local variable, which would have gone out of scope by the time control was returned to the calling function. (Undefined behaviour)
Another common dangling pointer example is an access of a memory location via pointer, after free has been explicitly called on that memory.
int *c = malloc(sizeof(int));
free(c);
*c = 3; //writing to freed location!
A memory leak is memory which hasn’t been freed, there is no way to access (or free it) now, as there are no ways to get to it anymore. (E.g. a pointer which was the only reference to a memory location dynamically allocated (and not freed) which points somewhere else now.)
void func(){
char *ch = malloc(10);
}
//ch not valid outside, no way to access malloc-ed memory
Char-ptr ch is a local variable that goes out of scope at the end of the function, leaking the dynamically allocated 10 bytes.