"Joseph S. Myers" <[EMAIL PROTECTED]> writes: | On Mon, 14 Feb 2005, Matt Austern wrote: | | > What was the rationale behind issuing this warning? I find it rather | > unfriendly. In this example, after all, the user isn't doing anything wrong. | > scalb is not defined in any standard that I can see, and users have every | > right to declare a function called scalb with whatever types they like. | | scalb is defined in POSIX (albeit as obsolescent). Reusing an identifier | with external linkage to refer to something other than the standard | function with that name yield undefined behavior. We don't yet have the
But the program at issue does not invoke anything having to do with POSIX, it makes no sense to pretend it has undefined behaviour. IMO, the C++ front-end does the right thing. After all, POSIX is just a C binding, with contradictroy requirements. | facility to specify to the compiler that you are using functions from a | particular version of POSIX (for example), so those should be built in but | other extensions should not (although -std=c89 or -std=c99 will disable | built-ins outside the selected standard), and nor do we any longer have a | way of distinguishing from the DECL of a built-in function whether it is | one from the selected C standard or otherwise, which is one factor which | could affect whether to warn, although we did used to have | DECL_BUILT_IN_NONANSI and could add it back again if useful. | | The fine-grained way to disable this warning is by disabling the built-in | function with -fno-builtin-scalb. | | > Earlier versions of the compiler did not issue this warning, and the C++ front | > end still doesn't. I'd like to see this warning removed, or at the very | > least tamed. | | 3.4.3 does issue the warning. If you use a function such as "abs" which | is built-in in the earlier versions, they issue the warning as well (on | all the versions I tested from 3.3.4 back to 2.7.2.3). There is a difference between "abs" and "scalb". | | Built-in function handling is naturally somewhat different for C++; there | are no implicit function declarations and standard functions must be | declared through use of the appropriate system header. But it would seem | reasonable for the C++ compiler to warn as well for extern "C" | declarations conflicting with built-in functions. having the C++ front-end misbehaves as the C front-end does on scalb would be the wrong path. -- Gaby
