/*****************************************************************************
*                                                                            *
*               ==============================================               *
*                                                                            *
*****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>

#define usage() fprintf(stderr, "usage: %s inputfile outputfile key\n", progammname)


/*****************************************************************************
*                                                                            *
*  --------------------------------- main ---------------------------------  *
*                                                                            *
*****************************************************************************/

int main(int argc, char *argv[]) {

/*Programmname merken*/
char *progammname = argv[0];
int inputfile;
int outputfile;
int anz_gelesen;
unsigned long key;
unsigned long gelesen;
			
/*Argumentverarbeitung, */
/*falls filename angegeben wird in diesen geschrieben, sonst auf stdout*/
if (argc == 4)
{
	inputfile = open(argv[1],O_RDONLY);

	if(inputfile == -1)
	{
		fprintf(stderr,"Fehler beim Oeffnen der Datei %s zum Lesen.\n", argv[1]);		
		usage();
		return -1;
	}
	else
	{
		/*outputfile = creat(argv[2], 0777);*/
		outputfile = open(argv[2], O_WRONLY | O_APPEND | O_TRUNC | O_CREAT, 0777);

		if(outputfile == -1)
		{
			close(inputfile);
			fprintf(stderr,"Fehler beim Oeffnen der Datei %s zum Schreiben.\n", argv[2]);		
			usage();
			return -1;
		}	
	}
	sscanf(argv[3], "%lu", &key);	
	fprintf(stdout,"Key: %lu\n", key);
}
else
{
	usage();
	return -1;
}

while ((anz_gelesen = read(inputfile, (char*)&gelesen, 4)) > 0)
{
	gelesen = gelesen ^key;
	write(outputfile, (char*)&gelesen, anz_gelesen);	
	gelesen = 0;
	anz_gelesen = 0;
}
close(inputfile);
close(outputfile);
return 0;

}