Get file's group name in Cocoa

group.m

#import <Foundation/Foundation.h>
#include <grp.h>
#include <string.h>
#include <sys/stat.h>

@interface FileOwnerManager : NSObject
- (BOOL)isWheelPresent:(NSString *)path;
@end

@implementation FileOwnerManager

- (BOOL)isWheelPresent:(NSString *)path
{
    struct stat f_stat;
    int res = stat([path UTF8String], &f_stat);
    if (res != 0) {
        NSLog(@"Error!");
        return NO;
    }
    struct group *group = getgrgid(f_stat.st_gid);
    NSLog(@"%@: %s", path, group->gr_name);
    return strcmp(group->gr_name, "wheel") == 0;
}

@end

int main(int argc, char **argv)
{
    BOOL res = NO;
    @autoreleasepool {
        FileOwnerManager *fom = [[FileOwnerManager alloc] init];
        res = [fom isWheelPresent:[NSString stringWithUTF8String:argv[1]]];
        [fom release];
    }
    return res ? 0 : 1;
}