[gentoo-user] Unknown gcc-version needed by nvidia-cuda-toolkit?

Hi,

while doing the update of my system I got this:

Calculating dependencies... done!
 * Dependencies could not be completely resolved due to
 * the following required packages not being installed:
 * 
 *   <sys-devel/gcc-7[cxx] pulled in by:
 *     dev-util/nvidia-cuda-toolkit-9.1.85

Installed is this:

[I] sys-devel/gcc
     Available versions:  
     (2.95.3) [M]~*2.95.3-r10^s
     (3.3.6) [M](~)3.3.6-r1^s
     (3.4.6) [M]3.4.6-r2^s
     (4.0.4) [M]**4.0.4^s
     (4.1.2) [M]4.1.2^s
     (4.2.4) [M](~)4.2.4-r1^s
     (4.3.6) [M]4.3.6-r1^s
     (4.4.7) [M]4.4.7^s
     (4.5.4) [M]4.5.4^s
     (4.6.4) [M]4.6.4^s
     (4.7.4) [M]4.7.4-r1^s
     (4.8.5) [M]4.8.5-r1^s
     (4.9.4) [M]4.9.4^s
     (5.4.0) [M]5.4.0-r4^s
     (6.4.0) [m]6.4.0^s [m]6.4.0-r1^s
     (7.2.0) (~)7.2.0^s (~)7.2.0-r1^s
     (7.3.0) (~)7.3.0^s **7.3.0-r1^s
       {altivec awt boundschecking cilk +cxx d debug doc fixed-point +fortran gcj go graphite hardened jit libssp mpx mudflap multilib +nls nopie nossp +nptl objc objc++ objc-gc +openmp +pch pgo +pie regression-test +sanitize +ssp vanilla +vtv}
     Installed versions:  7.3.0(7.3.0)^s(11:19:06 PM 02/02/2018)(cxx fortran nls nptl openmp pch pie sanitize ssp vtv -altivec -awt -cilk -debug -doc -fixed-point -gcj -go -graphite -hardened -jit -libssp -mpx -multilib -objc -objc++ -objc-gc -pgo -regression-test -vanilla)
     Homepage:            https://gcc.gnu.org/
     Description:         The GNU Compiler Collection

[I] sys-devel/gcc-config
     Available versions:  1.8-r1 (~)1.9.0-r1 (~)1.9.1 **9999
     Installed versions:  1.9.1(02:25:19 AM 12/17/2017)
     Homepage:            https://gitweb.gentoo.org/proj/gcc-config.git/
     Description:         Utility to manage compilers

Found 2 matches


...I think, that gcc-7.3.0 matches  <sys-devel/gcc-7[cxx]...

But what is the 'c' in '[cxx]' for? And why is the installation of the
gcc not recognized as espected?

Cheers
Meino