getgroups(2)                                               getgroups(2)

  getgroups()

  NAME

    getgroups() - retrieve supplementary group ID list

  SYNOPSIS

    #include 
    #include 

    int getgroups (int gidsetsize, gid_t grouplist[])

  DESCRIPTION

    The getgroups(2) function reads through the group database and fills the
    grouplist array with the supplementary group IDs of the calling process.

    The argument gidsetsize specifies the number of elements in the supplied
    array, which cannot be larger than NGROUPS_MAX.

    If gidsetsize is set to 0, the return value is the number of supplemental
    group IDs associated with the calling process, and the grouplist array is
    not modified.

    On Windows, groups and users share the same name space in the user
    accounts database.

  RETURN VALUES

    The getgroups(2) function returns the number of supplementary group IDs
    filled in the grouplist array. On error, it returns -1.

  ERRORS

    The getgroups(2) function fails because:

    [EINVAL]
        The gidsetsize argument isn't equal to 0 and is less than the number
        of supplementary group IDs.

  SEE ALSO

    getgrnam(2)

    getpwnam(2)

  USAGE NOTES

    The getgroups function is thread safe.

    The getgroups function is async-signal safe.