Question

my effort to understand pointers better, I wrote this code:

int *a = 17;

printf("%d", a+3);

It compiled fine under c using gcc-4.3.4: http://ideone.com/abotd

And yet it failed to compile with c++: http://ideone.com/IdGHy

I would like to know why.

Also, the output, as you can see from the first link is 29. I pseudo-understand what’s happening: sizeof(int) is 4, and when I wrote a+3 instead of adding 3 to 17, 3*4 is being added.

Still, I would appreciate if someone can explain it more eloquently.

Thanks!

Answer 1

For C++ version try this:

int *a = (int *)17;
printf("%d", a + 3);

And yes your explanation is correct…

This is called pointer arithmetic and works the way you said. Note however that the code you are using here where you assign a constant value to a pointer to an int is rarely done in real life. The pointer value usually comes from some kind of memory allocation functions e.g malloc in C or new in C++ (although new isn’t a function).