group_member - test whether a process is in a group

#include <unistd.h>
int group_member(gid_t gid);

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

    _GNU_SOURCE

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

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)