C小程序 - 从用户id或组id获得用户名或组名

#include
char *uid_to_name( uid_t uid )
{
    struct    passwd *getpwuid(), *pw_ptr;
    static  char numstr[10];

    if ( ( pw_ptr = getpwuid( uid ) ) == NULL ){
        sprintf(numstr,"%d", uid);
        return numstr;
    }
    else
        return pw_ptr->pw_name ;
}

#include    <grp.h>
char *gid_to_name( gid_t gid )
{
    struct group *getgrgid(), *grp_ptr;
    static  char numstr[10];

    if ( ( grp_ptr = getgrgid(gid) ) == NULL ){
        sprintf(numstr,"%d", gid);
        return numstr;
    }
    else
        return grp_ptr->gr_name;
}