On Tue, 1 Oct 2019 at 15:59, Edward Diener <eldlistmailingz@xxxxxxxxxxxxxx> wrote: > > On 10/1/2019 7:13 AM, Jonathan Wakely wrote: > > On Tue, 1 Oct 2019 at 01:25, Edward Diener wrote: > >> How do I find out, for a given gcc compiler product such as gcc-9.2, > >> what the gnu extensions are when I specify '-std=c++nn' and when I > >> specify '-std=gnu++nn' for any given valid 'nn' ? When I look in the > >> documentation for '-std' in gcc-9.2 the only explanation I can see at > >> https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/C-Dialect-Options.html#C-Dialect-Options > >> does not give me that information. Does it exist somewhere online or in > >> the gcc docs ? > > > > The documented extensions (and when they are enabled) are covered in > > https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/#toc-Extensions-to-the-C-Language-Family > > and https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/#toc-Extensions-to-the-C_002b_002b-Language > > (or just search for "extensions" in the TOC). > > > > Thanks for the links. But I am trying to understand the difference > between, let's say, '-std=c++17' and '-std=gnu++17'. Clearly they can > not be offering the exact same gnu extensions, else there would not be > two different settings for the C++ standard 2017 in gcc. Wrong. They could enable exactly the same set of extensions. It would be confusing and annoying to users to *not* provide a -std=gnu++17 option given that we have -std=c++NN and -std=gnu++NN for every previous standard. So it's wrong to assume "clearly" they can't mean the same thing. > You have said > that '-std=c++17' is not necessarily just the C++17 standard but may > also include some gnu extensions. So the gnu extensions included in > '-std=c++17' must be different than the gnu extensions included in > '-std=gnu++17'. No, as above. > How is it possible to find out the difference in gnu > extensions between the two ? Is there any documentation that explains > that difference, or is it left for the programmer to experiment and see > what is there in each case ? Read the manual sections I linked to. For each extension, if it conflicts with the base standard it will only be enabled for the gnu++NN modes, not the c++NN modes, and should be documented as such. I'm not going to do reading that for you.
