home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Power Programmierung
/
Power-Programmierung (Tewi)(1994).iso
/
magazine
/
pctchnqs
/
1990
/
number1
/
l1.c
< prev
next >
Wrap
Text File
|
1989-07-29
|
1KB
|
46 lines
/*
* *** Listing 1 ***
*
* Program to calculate the 16-bit checksum of all bytes in the
* specified file. Obtains the bytes one at a time via read(),
* letting DOS perform all data buffering.
*/
#include <stdio.h>
#include <fcntl.h>
main(int argc, char *argv[]) {
int Handle;
unsigned char Byte;
unsigned int Checksum;
int ReadLength;
if ( argc != 2 ) {
printf("usage: checksum filename\n");
exit(1);
}
if ( (Handle = open(argv[1], O_RDONLY | O_BINARY)) == -1 ) {
printf("Can't open file: %s\n", argv[1]);
exit(1);
}
/* Initialize the checksum accumulator */
Checksum = 0;
/* Add each byte in turn into the checksum accumulator */
while ( (ReadLength = read(Handle, &Byte, sizeof(Byte))) > 0 ) {
Checksum += (unsigned int) Byte;
}
if ( ReadLength == -1 ) {
printf("Error reading file %s\n", argv[1]);
exit(1);
}
/* Report the result */
printf("The checksum is: %u\n", Checksum);
exit(0);
}