Question

I was noticing some wording changes to section 5.6 for C++11. (I’m looking at the draft C++ standard N3242, dated 2011-02-28.) The new (draft) standard includes the sentence:

“For integral operands the / operator yields the algebraic quotient with any fractional part discarded;”

This statement is not in 5.6 of the 03 standard (ISO-IEC-14882-2003), but I don’t think this is a change, is it? This is how C and C++ has worked for years unless I’ve lost my mind (which may have happened anyway).

Answer 1

You’re not going mad.

A footnote to 5.6/4 said:

[C++03 footnote 74]: According to work underway toward the revision
of ISO C, the preferred algorithm for integer division follows the
rules defined in the ISO Fortran standard, ISO/IEC 1539:1991, in which
the quotient is always rounded toward zero.

In C++11 this behaviour is explicitly required rather than being “preferred”; the change is listed in the compatibility section:

[C++11: C.2.2]:
Change: Specify rounding for results of integer / and %
Rationale: Increase portability, C99 compatibility.
Effect on original feature: Valid C++ 2003 code that uses integer division
rounds the result toward 0 or toward negative infinity, whereas this
International Standard always rounds the result toward 0.