Package: gcc-9 Version: 9.2.1-22 Severity: normal The -std=c11 option (or other versions of the C standard) prevents the use of decimal FP:
$ cat tst.c int main (void) { _Decimal64 x = 1; return x != 1; } $ gcc-9 tst.c -o tst $ gcc-9 -std=c11 tst.c -o tst tst.c: In function ‘main’: tst.c:3:3: error: unknown type name ‘_Decimal64’ 3 | _Decimal64 x = 1; | ^~~~~~~~~~ There is no such issue with gcc-snapshot (_Decimal64 is not a forbidden extension): $ gcc-snapshot -std=c11 tst.c -o tst $ gcc-snapshot -std=c11 -pedantic tst.c -o tst tst.c: In function 'main': tst.c:3:3: warning: ISO C does not support decimal floating-point before C2X [-Wpedantic] 3 | _Decimal64 x = 1; | ^~~~~~~~~~ The GCC 9.2.0 manual does not mention a possible limitation. -- System Information: Debian Release: bullseye/sid APT prefers unstable-debug APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 5.4.0-2-amd64 (SMP w/12 CPU cores) Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=POSIX, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=POSIX (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages gcc-9 depends on: ii binutils 2.33.50.20200107-1 ii cpp-9 9.2.1-22 ii gcc-9-base 9.2.1-22 ii libc6 2.29-8 ii libcc1-0 9.2.1-22 ii libgcc-9-dev 9.2.1-22 ii libgcc1 1:9.2.1-22 ii libgmp10 2:6.1.2+dfsg-4 ii libisl22 0.22-2 ii libmpc3 1.1.0-1 ii libmpfr6 4.0.2-1 ii libstdc++6 9.2.1-22 ii zlib1g 1:1.2.11.dfsg-1+b1 Versions of packages gcc-9 recommends: ii libc6-dev 2.29-8 Versions of packages gcc-9 suggests: ii gcc-9-doc 9.2.0-2 ii gcc-9-locales 9.2.1-22 ii gcc-9-multilib 9.2.1-22 -- no debconf information