On 2017-06-01 14:22:19 +0200, David Brown wrote: > The compiler cannot blacklist <stdint.h> in pedantic C90 mode without > breaking C90 compatibility. The C90 standards say nothing about > <stdint.h> - it is therefore just as legitimate a header name as <foo.h> > would be. The compiler cannot retroactively reserve file names from > future standards in the way you suggest. I agree without -pedantic, but with -pedantic, this is different. > > If you want an example: > > > > -Woverlength-strings > > Warn about string constants that are longer than the "minimum > > maximum" length specified in the C standard. Modern compilers > > generally allow string constants that are much longer than the > > standard's minimum limit, but very portable programs should avoid > > using longer strings. > > > > The limit applies after string constant concatenation, and does not > > count the trailing NUL. In C90, the limit was 509 characters; in > > C99, it was raised to 4095. C++98 does not specify a normative > > minimum maximum, so we do not diagnose overlength strings in C++. > > > > This option is implied by -Wpedantic, and can be disabled with > > -Wno-overlength-strings. > > > > That is totally different - that is an option specifically applying a > limit that is not required by any standard, but which can be helpful in > checking code for portability. I don't see any difference. Including <stdint.h> unconditionally is also a portability issue. > Even if the compiler were to have a "-Wblacklist-stdint" option, that > might help you detect it - but it would break C90 standards > compatibility, because C90 /allows/ you to have a <stdint.h>. Similarly, C90 allows one to have strings longer than the C90 limit. Really, -Wblacklist-stdint would be very similar to -Woverlength-strings in that sense. > The C90 standards document does not explicitly discuss extended integer > types (which are mentioned in C11, and I think C99 but I haven't > checked). But there is nothing in the standard to stop an > implementation having them - it just has to use reserved identifiers for > them. But I recall that here, the context is portability detection with -pedantic (see above). > I still have trouble understanding why this is an issue. If you are > writing code that needs to be C90 compatible, don't include <stdint.h> > and don't use intmax_t. Problem solved. So, you are saying: If you are writing code that needs to be C90 compatible, just write code that it C90 compatible. Problem solved. And there is no need for -pedantic. So, why is -pedantic there??? > To quote from the gcc reference for -Wpedantic: > > > -Wpedantic does not cause warning messages for use of the alternate > > keywords whose names begin and end with ‘__’. Pedantic warnings are > > also disabled in the expression that follows __extension__. However, > > only system header files should use these escape routes; application > > programs should avoid them. See Alternate Keywords. > > > > Some users try to use -Wpedantic to check programs for strict ISO C > > conformance. They soon find that it does not do quite what they want: > > it finds some non-ISO practices, but not all—only those for which ISO > > C requires a diagnostic, and some others for which diagnostics have > > been added. > > > > A feature to report any failure to conform to ISO C might be useful > > in some instances, but would require considerable additional work and > > would be quite different from -Wpedantic. We don’t have plans to > > support such a feature in the near future. > > What you appear to be asking for is not supported by gcc, and not going > to be supported. Here I'm not asking a feature to detect any portability issue (indeed, this may be too complex), but a feature to detect a *particular* portability issue. I don't think that adding an option to blacklist <stdint.h> (implied by -Wpedantic in C90 mode) would be too complex. > I thought autoconf tests were run using specific test code, not the > actual source code you are distributing. Surely you can avoid > accidentally including <stdint.h> in the autoconf tests? The autoconf test is there to detect whether <stdint.h> is available. This is not by accident. > And surely a quick "grep" will ensure that it is not used in the > real source code? "grep" does not allow one to detect conditional use. > > The goal of -pedantic-errors is to *detect* that the developer writes > > something like the above instead of just: > > > > #include <stdint.h> > > > > Since #include <stdint.h> does not break C90 conformity, then no. So, why is -Woverlength-strings implied by -pedantic, though it does not break C90 conformity? > You /could/ ask for a warning flag -Wno-oversized-integers that would > warn on the use of anything larger than "long" in C90 and anything > larger than "long long" in C99 - much the same as -Woverlength-strings. Yes, I was thinking of such a warning flag. But I was also thinking that it would be implied by -pedantic, for consistency with -Woverlength-strings. -- Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
