7 ms·

Won't this break stuff?

nadams 11y ago
That's probably the reason why C++11 wasn't ever the default. Though, there are arguments about trying to be backwards compatible forever. My personal opinion is to leave it the way it is - or at the very least default to C++11 first.
- plorkyeran 11y ago
  C++14 didn't introduce any new breaking changes to pre-C++11 functionality, so switching to C++11 first would not make the migration now any easier and would introduce the need for another migration in the future.
nly 11y ago
It shouldn't. 99.5% of C++98 code is valid C++14. Code compiled as C++98 and code compiled as C++14, should also link.
- AnimalMuppet 11y ago
  So if my code is at least 200 lines long... (I know, it doesn't work like that. 99.5% means syntax elements or some such, not lines of code. But it still works out the same in a medium-to-large code base; 99.5% compatibility breaks more than you expect.)
- ridiculous_fish 11y ago
  I maintain a project that compiles as both C++11 and C++03. One pain point is that the headers have changed between them: #include <tr1/memory> to #include <memory>. This is complicated further by libc++, which doesn't have <tr1/memory>.
  - rleigh 11y ago
    That's fairly straightforward to work around, however. I've used both autoconf and cmake to do functional testing of which headers are available, and then include the most recent available out of <memory>, <tr1/memory> and <boost/shared_ptr.hpp>, bringing them into a project::compat namespace to make the codebase not need to care which is in use, and the same for a number of other tr1/boost types now in C++11/14. I'm now at the point where for some projects I've been able to strip out this entirely and just use the C++11 types directly.
    - gurkendoktor 11y ago
      That is relatively straightforward in the scope of a large project (and it's what I do as well), but stuff like this really makes it harder to share small-to-medium sized C++ libraries. I don't understand why C++03 didn't just use the std:: namespace.
  - Sanddancer 11y ago
    What about a preprocessor check based on the __cplusplus value? If it's 199711L, implement the C++03 defines, if not, implement the C++11 defines.
    - gurkendoktor 11y ago
      A quick Google search suggests that this won't work unless you also check for the MSVC version - sigh: http://stackoverflow.com/questions/14131454/visual-studio-2012-cplusplus-and-c-11 http://stackoverflow.com/questions/14131454/visual-studio-20...
      - StephanTLavavej 11y ago
        If we changed __cplusplus before implementing every single C++11 feature, the Internet would riot.
        lmm 11y ago
        If you're exposing __cplusplus=199711L then you really ought to continue to support #include <tr1/memory> (i.e. C++03 style). As long as you do that there's no problem and the suggested thing should work.
        plorkyeran 11y ago
        VC++ never used <tr1/memory> in the first place. That was purely a libstdc++ thing, and not something that TR1 or any C++ standard ever said to do.
        StephanTLavavej 11y ago
        Yep. (TR1 was published after C++03, they're totally different things.) What we did with TR1 was actually very friendly to migration - we provided std::tr1::meow in <meow> (in 2008 SP1), then in 2010 we aliased that to std::meow as C++0x was being finalized, then in 2012 we switched the True Name to std::meow and made std::tr1::meow the alias for back-compat. At some point in the future we'll probably remove the tr1 aliases completely. For the Technical Specifications, we're following their header directory and namespace rules (<experimental/meow>).
cremno 11y ago
Maybe. For example, GCC 5 changed the default for C from gnu89 to gnu11 and that broke the build of some Finnish amateur project: https://lkml.org/lkml/2014/10/19/94 https://lkml.org/lkml/2014/10/19/94 That's why projects that use GCC or a compatible compiler should use the -std option to set the targeted standard and not rely on the default.
- ajross 11y ago
  Pretty much. Taking the "will this break stuff?" worry to the logical extreme would mean that gcc should default to a pre-standarization K&R dialect and g++ to a cfront dialect contemporary with 1st edition Stroustrup. The world moves on. Though if you're an active project, moving along with the world is probably a better option than throwing in --std=c++really-old and deliberately refusing to use new stuff.
- rbanffy 11y ago
  Forcing the update of old code doesn't make me sad. Considering new versions of the language should be improvements over previous ones, it may be a good side effect. If your code breaks with the new compiler and language standard, just change your build options to explicitly use the previous one.
koenigdavidmj 11y ago
If you maintain one of the rare codebases that would break, then just add "--std=c++98" to your compiler flags. GCC has already been getting steadily more strict by default, or at least opt-in with -Wall -Werror. The last time we updated our build environment, we had to go in and #include all the headers that were formerly implicit (or #include-d by other headers), and add in the 'const' every time we referred to a string literal. The possibly-unassigned variable checker also got a lot more sophisticated and now would enter called functions.
- GFK_of_xmaspast 11y ago
  I've been lead to believe that gcc can't / won't add warnings to -Wall precisely because of all the codebases that have -Werror.
  - cpeterso 11y ago
    New versions of gcc routinely fail to compile Firefox out of the box. A good example was gcc 4.7's -Wunused-local-typedefs, which is part of -Wall. Local typedefs seem to be a common pattern in Firefox's generated C++ (for IDL bindings).
    - andrewchambers 11y ago
      This is why I think static bug checking and compiling should be two different tools. There is no reason to fail a build which used to run, even if it has bugs. Doing all those checks at build time is slowing the build down too.
      - deleted 11y ago
        [deleted]
      - plorkyeran 11y ago
        Splitting static checks and compiling into separate tools will not prevent your builds from breaking when you update your tools if you have your build process deliberately configured to break whenever a new warning appears. GCC adding new warnings will not break your builds if you do not specifically ask for it to by using -Werror (or having your CI system reject any builds that produce warnings). At least with clang, -Weverything is not measurably slower than no warnings at all on any vaguely realistic code base.
plq 11y ago
Actually, I'm more interested in when a GCC with this patch will be marked stable by one of the distros that I use.

That's probably the reason why C++11 wasn't ever the default. Though, there are arguments about trying to be backwards compatible forever. My personal opinion is to leave it the way it is - or at the very least default to C++11 first.

plorkyeran 11y ago
C++14 didn't introduce any new breaking changes to pre-C++11 functionality, so switching to C++11 first would not make the migration now any easier and would introduce the need for another migration in the future.

nly 11y ago

It shouldn't. 99.5% of C++98 code is valid C++14. Code compiled as C++98 and code compiled as C++14, should also link.

AnimalMuppet 11y ago
So if my code is at least 200 lines long... (I know, it doesn't work like that. 99.5% means syntax elements or some such, not lines of code. But it still works out the same in a medium-to-large code base; 99.5% compatibility breaks more than you expect.)
ridiculous_fish 11y ago
I maintain a project that compiles as both C++11 and C++03. One pain point is that the headers have changed between them: #include <tr1/memory> to #include <memory>. This is complicated further by libc++, which doesn't have <tr1/memory>.
- rleigh 11y ago
  That's fairly straightforward to work around, however. I've used both autoconf and cmake to do functional testing of which headers are available, and then include the most recent available out of <memory>, <tr1/memory> and <boost/shared_ptr.hpp>, bringing them into a project::compat namespace to make the codebase not need to care which is in use, and the same for a number of other tr1/boost types now in C++11/14. I'm now at the point where for some projects I've been able to strip out this entirely and just use the C++11 types directly.
  - gurkendoktor 11y ago
    That is relatively straightforward in the scope of a large project (and it's what I do as well), but stuff like this really makes it harder to share small-to-medium sized C++ libraries. I don't understand why C++03 didn't just use the std:: namespace.
- Sanddancer 11y ago
  What about a preprocessor check based on the __cplusplus value? If it's 199711L, implement the C++03 defines, if not, implement the C++11 defines.
  - gurkendoktor 11y ago
    A quick Google search suggests that this won't work unless you also check for the MSVC version - sigh: http://stackoverflow.com/questions/14131454/visual-studio-2012-cplusplus-and-c-11 http://stackoverflow.com/questions/14131454/visual-studio-20...
    - StephanTLavavej 11y ago
      If we changed __cplusplus before implementing every single C++11 feature, the Internet would riot.
      - lmm 11y ago
        If you're exposing __cplusplus=199711L then you really ought to continue to support #include <tr1/memory> (i.e. C++03 style). As long as you do that there's no problem and the suggested thing should work.
        plorkyeran 11y ago
        VC++ never used <tr1/memory> in the first place. That was purely a libstdc++ thing, and not something that TR1 or any C++ standard ever said to do.
        StephanTLavavej 11y ago
        Yep. (TR1 was published after C++03, they're totally different things.) What we did with TR1 was actually very friendly to migration - we provided std::tr1::meow in <meow> (in 2008 SP1), then in 2010 we aliased that to std::meow as C++0x was being finalized, then in 2012 we switched the True Name to std::meow and made std::tr1::meow the alias for back-compat. At some point in the future we'll probably remove the tr1 aliases completely. For the Technical Specifications, we're following their header directory and namespace rules (<experimental/meow>).

cremno 11y ago

Maybe. For example, GCC 5 changed the default for C from gnu89 to gnu11 and that broke the build of some Finnish amateur project: https://lkml.org/lkml/2014/10/19/94 https://lkml.org/lkml/2014/10/19/94 That's why projects that use GCC or a compatible compiler should use the -std option to set the targeted standard and not rely on the default.

ajross 11y ago
Pretty much. Taking the "will this break stuff?" worry to the logical extreme would mean that gcc should default to a pre-standarization K&R dialect and g++ to a cfront dialect contemporary with 1st edition Stroustrup. The world moves on. Though if you're an active project, moving along with the world is probably a better option than throwing in --std=c++really-old and deliberately refusing to use new stuff.
rbanffy 11y ago
Forcing the update of old code doesn't make me sad. Considering new versions of the language should be improvements over previous ones, it may be a good side effect. If your code breaks with the new compiler and language standard, just change your build options to explicitly use the previous one.

koenigdavidmj 11y ago

If you maintain one of the rare codebases that would break, then just add "--std=c++98" to your compiler flags. GCC has already been getting steadily more strict by default, or at least opt-in with -Wall -Werror. The last time we updated our build environment, we had to go in and #include all the headers that were formerly implicit (or #include-d by other headers), and add in the 'const' every time we referred to a string literal. The possibly-unassigned variable checker also got a lot more sophisticated and now would enter called functions.

GFK_of_xmaspast 11y ago
I've been lead to believe that gcc can't / won't add warnings to -Wall precisely because of all the codebases that have -Werror.
- cpeterso 11y ago
  New versions of gcc routinely fail to compile Firefox out of the box. A good example was gcc 4.7's -Wunused-local-typedefs, which is part of -Wall. Local typedefs seem to be a common pattern in Firefox's generated C++ (for IDL bindings).
  - andrewchambers 11y ago
    This is why I think static bug checking and compiling should be two different tools. There is no reason to fail a build which used to run, even if it has bugs. Doing all those checks at build time is slowing the build down too.
    - deleted 11y ago
      [deleted]
    - plorkyeran 11y ago
      Splitting static checks and compiling into separate tools will not prevent your builds from breaking when you update your tools if you have your build process deliberately configured to break whenever a new warning appears. GCC adding new warnings will not break your builds if you do not specifically ask for it to by using -Werror (or having your CI system reject any builds that produce warnings). At least with clang, -Weverything is not measurably slower than no warnings at all on any vaguely realistic code base.

plq 11y ago

Actually, I'm more interested in when a GCC with this patch will be marked stable by one of the distros that I use.