Verständnis Problem

[ltheonel]

Hallo, ich verstehe diese Zeile nicht, durch das %16 denkt man
:

  if(((i%16)==15) || (i == length-1)) {

        for (  j = 0; j < length; j++)

wieso i%16 rest 15 oder length-1 und dann das mit der j for schleife kann das wer villt versträndlicher erklären



Hier mal der ganze Code:

simple_server.h

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "hacking.h"

#define PORT 7790

int
main(void)
{

int sockfd, new_sockfd;
struct sockaddr_in host_addr, client_addr;
int recv_length=1, yes=1;
socklen_t sin_size;
char buffer[1024];

if((sockfd=(PF_INET, SOCK_STREAM, 0))==-1)
perror("in socket");

if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int))==-1)
perror("in setting options");

host_addr.sin_family = AF_INET;
host_addr.sin_port = htons(PORT);
host_addr.sin_addr.s_addr = 0;
memset(&(host_addr.sin_zero), '0', 8);
 


if(bind(sockfd, (struct sockaddr *)&host_addr, sizeof(struct sockaddr))==-1)
perror("in binding");

if(listen(sockfd, 5)==-1)
perror("in listening on socket");

while(1){

sin_size = sizeof(struct sockaddr_in);
new_sockfd = accept(sockfd, (struct sockaddr *) &client_addr, &sin_size);
if(new_sockfd == -1)
perror("accepting connection");

printf("server got connection from %s prot %d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

send(new_sockfd, "Hello, world!\n", 13,0);
recv_length = recv(new_sockfd,&buffer,1024,0);

while (recv_length > 0) {
    printf( "RECV: %d bytes\n", recv_length );
    dump(buffer, recv_length);
    recv_length = recv(new_sockfd, &buffer, 1024, 0);

}
close(new_sockfd);
}
return 0;
}

hacking.h :

void dump(const unsigned char *data_buffer, const unsigned int length) {
    unsigned char byte;
    unsigned int i,j;
    for ( i = 0; i < length; i++)
        {
        byte = data_buffer[i];
        printf( "%02x ", data_buffer[i]);
        if(((i%16)==15) || (i == length-1)) {

        for (  j = 0; j < length; j++)
                printf ("    ");
        printf( "|  " );
        for ( j =(i-(i%16)); j <= i; j++)
                {
                    byte = data_buffer[j];
            if((byte > 31) && (byte < 127))
            printf( "%c", byte );
            else
                printf( "." );
   
                }
        printf( "\n" );
}
}
}

[jeffcobb]

Last time I spoke German was like 25+ years ago but I think he/she is asking about why the modulus 15 || length-1 logic is what it is....my guess is that it is simply watching for the end of a line of data to format it assuming they want to break on every 16th (0-15) data item or if it is the last element in the buffer...just me guessing and my German is so old and unused that he might be asking for a biscuit recipe or something..

[ltheonel]

hey thanks for helping me even with picking wrong language...

i have a roblem with getting this

my guess is that it is simply watching for the end of a line of data to format it assuming they want to break on every 16th (0-15) data item or if it is the last element in the buffer

for example i is 15 then 15/16 = 0,9375

(rest = 9,375)

and thats not == 15

okay i understand that this is watching for end of i (i == length-1)


but what us that for ???
((i%16)==15) why rest 15

[Shakti]

With integer math 15/16 = 0, rest = 15. The modulus calculates the rest based on integer division and thus 15%16=15, just like 16%16=0, 17%16=1 (17/16=1, rest 1) and so on.