On 28 October 2013 21:13, Ian Lance Taylor wrote: > On Sun, Oct 27, 2013 at 12:04 PM, Gerald Pfeifer <ger...@pfeifer.com> wrote: >> To make it easier to reproduce builds of software and entire GNU/Linux >> distributions, RMS had the idea of adding a warning to GCC that warns >> about the use of __DATE__ and __TIME__. >> >> Short of "interesting" changes to the environment or #defining these >> two, as soon as a program uses __DATE__ or __TIME__ at least once, >> builds of the program will differ for that reason alone. (There are >> others, but one step at a time; this is not the point of this mail). >> >> I was thinking a new warning -Wdate-time or similar could address >> this. > > I don't have any strong objection, but I'll note that it's even easier > to use -D options. > > CC='gcc -D__DATE__=today'
It's undefined behaviour in both C and C++ to redefine pre-defined macros such as __DATE__ or __TIME__. The undefined behaviour study group of the C++ committee are considering making it ill-formed, which would require a diagnostic.
