Narrowing conversions in C++0x. Is it just me, or does this sound like a breaking change?

Question

C++0x is going to make the following code and similar code ill-formed, because it requires a so-called narrowing conversion of a double to a int<

Answer 1

It was indeed a breaking change as real life experience with this feature has shown gcc had turned narrowing into a warning from an error for many cases due to real life pains with porting C++03 code bases to C++11. See this comment in a gcc bug report:

The standard only requires that "a conforming implementation shall issue at least one diagnostic message" so compiling the program with a warning is allowed. As Andrew said, -Werror=narrowing allows you to make it an error if you want.

G++ 4.6 gave an error but it was changed to a warning intentionally for 4.7 because many people (myself included) found that narrowing conversions where one of the most commonly encountered problems when trying to compile large C++03 codebases as C++11. Previously well-formed code such as char c[] = { i, 0 }; (where i will only ever be within the range of char) caused errors and had to be changed to char c[] = { (char)i, 0 }