CODEWITHSUNDEEP
c++
user3344003
user3344003

Reputation: 21637

Type of pointer arithmetic

I am looking at some old code of mine that manipulates data buffers. I have many places that have:

char *ptr1 ;
char *ptr2 ;

And then I need to find the number of bytes between the two.

int distance = ptr2 - ptr1 ;

I am getting a lot of warnings about truncation. What is the type of 

 ptr2 - ptr1

I have found a number of answers dealing with pointer arithmetic but, oddly not an answer to this particular question.

Pointer Arithmetic

Upvotes: 4

Views: 2140

Answers (1)

GManNickG
GManNickG

Reputation: 504073

The result of subtracting two pointers† is a std::ptrdiff_t. It is an implementation-defined signed integer; it could be larger than what an int could store.

See http://en.cppreference.com/w/cpp/types/ptrdiff_t for more information.

†You can only subtract pointers if they point to elements of the same array, otherwise it's UB.

Upvotes: 8

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