4 ms·

we now have the new ISO C11 standard. C11 includes a number of new features that parallel those in C++11 Did i miss something?

by beza1e1 15y ago

pavlov 15y ago
ISO C11 has been known as "C1x" until its standardization: http://en.wikipedia.org/wiki/C1X http://en.wikipedia.org/wiki/C1X Nothing earth-shaking. The _Generic keyword is probably the most exotic addition (at least among those listed on the Wikipedia page) -- it's basically switch(typeof(X)) for macros.
- derleth 15y ago
  Is there a reason C11 doesn't include typeof? It's been a gcc extension for decades now, and I see no reason it can't be part of the official standard.
  - nitrogen 15y ago
    My guess as someone who is not familiar with compiler internals is that the design of many compilers prevents them from implementing a typeof() operator without major changes to the way they analyze and store the parsed source code, so the standard writers decided not to include a feature that would not be widely implemented. But, using _Generic(), one can do many of the things one would do with typeof(). For example, the max() example in [0] could probably be implemented using at most n^2 separate macros plus a _Generic() macro for each type, where n is the number of arithmetic types (though I think you'd still need GCC's statements within expressions in order to evaluate A and B only once). I'm thinking something like this that combines the cbrt(X) example from the C1x spec [1] (§6.5.1.1 paragraph 5) with the gcc max() example, though I haven't tested it, and it could almost certainly be simplified by exploiting type promotion rules: #define max_ld_ld(A, B) ({long double _a = (A); \ long double _b = (B); _a > _b ? _a : _b}) #define maxld(A, B) _Generic((B), \ long double: max_ld_ld, \ int: max_ld_i, \ /* etc. */ \ )((A), (B)) #define maxi(A, B) _Generic((B), \ long double: max_i_ld, \ int: max_i_i, \ /* etc. */ \ )((A), (B)) #define max(A, B) _Generic((A), \ long double: maxld, \ int: maxi, \ /* etc. */ \ )((A), (B)) [0] http://gcc.gnu.org/onlinedocs/gcc/Typeof.html http://gcc.gnu.org/onlinedocs/gcc/Typeof.html [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf OT P.S. It is very annoying that Google has broken right-click+copy URL.
  - ouah 15y ago
    The case of typeof has already been discussed for C99 and it has been rejected. In ISO C99 Rationale document (section 6.7.7), it is written: "A proposed typeof operator was rejected on the grounds of insufficient utility." Don't forget most of the work of the C committee is spent in resisting features suggestions.

we now have the new ISO C11 standard. C11 includes a number of new features that parallel those in C++11 Did i miss something?

by beza1e1 15y ago

we now have the new ISO C11 standard. C11 includes a number of new features that parallel those in C++11 Did i miss something?

pavlov 15y ago

ISO C11 has been known as "C1x" until its standardization: http://en.wikipedia.org/wiki/C1X http://en.wikipedia.org/wiki/C1X Nothing earth-shaking. The _Generic keyword is probably the most exotic addition (at least among those listed on the Wikipedia page) -- it's basically switch(typeof(X)) for macros.

derleth 15y ago
Is there a reason C11 doesn't include typeof? It's been a gcc extension for decades now, and I see no reason it can't be part of the official standard.
- nitrogen 15y ago
  My guess as someone who is not familiar with compiler internals is that the design of many compilers prevents them from implementing a typeof() operator without major changes to the way they analyze and store the parsed source code, so the standard writers decided not to include a feature that would not be widely implemented. But, using _Generic(), one can do many of the things one would do with typeof(). For example, the max() example in [0] could probably be implemented using at most n^2 separate macros plus a _Generic() macro for each type, where n is the number of arithmetic types (though I think you'd still need GCC's statements within expressions in order to evaluate A and B only once). I'm thinking something like this that combines the cbrt(X) example from the C1x spec [1] (§6.5.1.1 paragraph 5) with the gcc max() example, though I haven't tested it, and it could almost certainly be simplified by exploiting type promotion rules: #define max_ld_ld(A, B) ({long double _a = (A); \ long double _b = (B); _a > _b ? _a : _b}) #define maxld(A, B) _Generic((B), \ long double: max_ld_ld, \ int: max_ld_i, \ /* etc. */ \ )((A), (B)) #define maxi(A, B) _Generic((B), \ long double: max_i_ld, \ int: max_i_i, \ /* etc. */ \ )((A), (B)) #define max(A, B) _Generic((A), \ long double: maxld, \ int: maxi, \ /* etc. */ \ )((A), (B)) [0] http://gcc.gnu.org/onlinedocs/gcc/Typeof.html http://gcc.gnu.org/onlinedocs/gcc/Typeof.html [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf OT P.S. It is very annoying that Google has broken right-click+copy URL.
- ouah 15y ago
  The case of typeof has already been discussed for C99 and it has been rejected. In ISO C99 Rationale document (section 6.7.7), it is written: "A proposed typeof operator was rejected on the grounds of insufficient utility." Don't forget most of the work of the C committee is spent in resisting features suggestions.