group_member - test whether a process is in a group

       The  group_member()  function  tests  whether any of the caller's supplementary group IDs (as returned by
       getgroups(2)) matches gid.

       Standard C library (libc, -lc)

       group_member - test whether a process is in a group

       The group_member() function returns nonzero if any of the caller's supplementary group IDs  matches  gid,
       and zero otherwise.

getgid(2), getgroups(2), getgrouplist(3), group(5)

Linux man-pages 6.9.1                              2024-05-02                                    group_member(3)

       GNU.

#include<unistd.h>intgroup_member(gid_tgid);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       group_member():
           _GNU_SOURCE