Simple replica of `id` command

id.c

#include <stdio.h>
#include <pwd.h>
#include <unistd.h>
#include <stdlib.h>
#include <grp.h>
#include <string.h>

void main( int argc, char *argv[] ) {
	struct passwd *user;
	struct group *group;
	uid_t uid = getuid();
	char response[1000];
	
	if( ( user = getpwuid( uid ) ) == NULL ) {
		perror( "getpwuid" );
		exit(1);
	}

	if( ( group = getgrgid( user->pw_gid ) ) == NULL ) {
		perror( "getgrgid" );
		exit(1);
	}

	sprintf( response, "uid=%d(%s) gid=%d(%s) groups=", uid, user->pw_name, user->pw_gid, group->gr_name );

	while( ( group = getgrent() ) != NULL ) {
		char gr_data[256];

		while( *group->gr_mem != NULL ) {
			if( strcmp( *group->gr_mem, user->pw_name ) == 0 ) {
				sprintf( gr_data, "%d(%s),", group->gr_gid, group->gr_name );
				strcat( response, gr_data );
			}
			group->gr_mem++;
		}
	}
	endgrent();
	response[strlen( response )-1] = '\0'; // Remove last comma
	printf("%s\n", response );
}