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Tip of the Day
Language: C++
Expertise: All
Sep 16, 1999

Uses of the ptrdiff_t Data Type

C and C++ define a special type for pointer arithmetic, namely ptrdiff_t, which is a typedef of a platform-specific signed integral type. You can use a variable of type ptrdiff_t to store the result of subtracting and adding pointers. For example:
#include <stdlib.h>
int main()
  int buff[4];
  ptrdiff_t diff = (&buff[3]) - buff; // diff = 3
  diff = buff -(&buff[3]); //  -3
What are the advantages of using ptrdiff_t? First, the name ptrdiff_t is self-documenting and helps the reader understand that the variable is used in pointer arithmetic exclusively. Secondly, ptrdiff_t is portable: its underlying type may vary across platforms, but you don't need to make changes in the code when porting it.
Danny Kalev
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