This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See for the official list.


566. Conversion of negative floating point values to integer type

Section: 7.3.11  [conv.fpint]     Status: NAD     Submitter: Seungbeom Kim     Date: 13 March 2006

Section 7.3.11 [conv.fpint] paragraph 1 states:

An rvalue of a floating point type can be converted to an rvalue of an integer type. The conversion truncates; that is, the fractional part is discarded.

Here, the concepts of “truncation” and “fractional part” seem to be used without precise definitions. When -3.14 is converted into an integer, is the truncation toward zero or away from zero? Is the fractional part -0.14 or 0.86? The standard seem to give no clear answer to these.

Suggested resolution:

  1. Replace “truncates” with “truncates toward zero.”

  2. Replace “the fractional part” with “the fractional part (where that of x is defined as x-floor(x) for nonnegative x and x-ceiling(x) for negative x);” there should be a better wording for this, or the entire statement “that is, the fractional part is discarded” can be removed, once the meaning of “truncation” becomes unambiguous as above.

Rationale (October, 2006):

The specification is clear enough: “fractional part” refers to the digits following the decimal point, so that -3.14 converted to int becomes -3.