comp.lang.c FAQ list · Question 4.5

Q: I have a char * pointer that happens to point to some ints, and I want to step it over them. Why doesn't

((int *)p)++;

work?

A: In C, a cast operator does not mean ``pretend these bits have a different type, and treat them accordingly''; it is a conversion operator, and by definition it yields an rvalue, which cannot be assigned to, or incremented with ++. (It is either an accident or a deliberate but nonstandard extension if a particular compiler accepts expressions such as the above.) Say what you mean: use

	p = (char *)((int *)p + 1);

or (since p is a char *) simply

	p += sizeof(int);

or (to be really explicit)

	int *ip = (int *)p;
	p = (char *)(ip + 1);

When possible, however, you should choose appropriate pointer types in the first place, rather than trying to treat one type as another.