c++ - Delete a pointer after the arithmetics

Question

int main() {
  int* i = new int(1);
  i++;
  *i=1;
  delete i;
}

Here is my logic:

I increment I by 1, and then assign a value to it. Then I delete the I, so I free the memory location while leaking the original memory. Where is my problem?

I also tried different versions. Every time, as long as I do the arithmetics and delete the pointer, my program crashes.

Answer 1

What your program shows is several cases of undefined behaviour:

1. You write to memory that hasn't been allocated (*i = 1)
2. You free something that you didn't allocate, effectively delete i + 1.

You MUST call delete on exactly the same pointer-value that you got back from new - nothing else. Assuming the rest of your code was valid, it would be fine to do int *j = i; after int *i = new int(1);, and then delete j;. [For example int *i = new int[2]; would then make your i++; *i=1; valid code]