On 30/11/16 17:07, Georg-Johann Lay wrote: > On 30.11.2016 15:32, Paul "LeoNerd" Evans wrote: >> On Wed, 30 Nov 2016 18:18:11 +0530 >> Senthil Kumar Selvaraj <senthil_kumar.selva...@atmel.com> wrote: >> >>> Diogo Martins Silva writes: >>> >>>> Hello all. >>>> >>>> The avr-gcc wiki (https://gcc.gnu.org/wiki/avr-gcc) lists 24 bits >>>> (u)ints as an extension since version 4.7. How do I use them? >>> >>> Use __uint24 as the type. Like so >>> >>> $ cat test.c >>> volatile __uint24 x; >>> int main() { >>> x++; >>> x--; >>> } >> >> Is it possible to get that added to <stdint.h> as the expected names >> >> int24_t >> uint24_t >> >> ? > > The C99 and later standards don't supply these types or reserve these > identifiers. Since C99, "int8_t" is an identifier that resides in the > namespace of the implementation, whereas "int24_t" is still in the > namespace of the application. Hence, for the new 3-byte types names > were chosen that are in the namespace of the implementation, i.e. > reserved identifiers which start with "__" (__int24 and __uint24). > > If you like you can define such types in your application, but they > should not go into any standard header. > > Johann
Actually, names such as int24_t and uint24_t /are/ reserved for the implementation to use in <stdint.h>. See 7.31.10 of the C11 standards under "Future library directions". (I don't know if the same applies to C99 - I don't have that standard conveniently on hand.) Types int24_t and uint24_t are optional, even if the compiler supports them as an integer type (unlike the 8, 16, 32 and 64 bit types). However, if int24_t and uint24_t are defined in <stdint.h>, then the implementation must also define printf and scanf format specifier macros PRId24, PRIi24, etc., in <inttypes.h>. This in turn implies that printf and scanf must support the types. These can be avoided by classifying avr-gcc as a "freestanding" compiler rather than a "hosted" compiler, but I believe the norm in gcc is that an integer type only goes in <stdint.h> if it is completely supported throughout the compiler and library, including printf support. So in gcc on 64-bit systems, the __int128 and __uint128 types don't have printf support, nor is there any way to make literals of these types (assuming the target does not have 128-bit long long's) - thus they are not considered "extended integer types" and don't have corresponding <stdint.h> types. For 24-bit integers in avr-gcc, it /would/ be possible to make a conforming freestanding C implementation with the types defined in <stdint.h> - but it would be inconsistent with other ports of gcc and with the printf in the library, and therefore probably not a good idea. mvh., David _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
