Question 4.5

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?

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 an anomaly in pcc-derived compilers, and an extension in gcc, that expressions such as the above are ever accepted.) Say what you mean: use

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

or (since p is a char *) simply

	p += sizeof(int);

Whenever possible, you should choose appropriate pointer types in the first place, instead of trying to treat one type as another.

References: K&R2 Sec. A7.5 p. 205
ANSI Sec. 3.3.4 (esp. footnote 14)
ISO Sec. 6.3.4
Rationale Sec. 3.3.2.4
H&S Sec. 7.1 pp. 179-80

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