Question

The program is done in C. This program opens a file containing binary or text and reads every byte in the file and writes both the ASCII hex value for that byte as well as it’s printable (human-readable) character (characters, digits, symbols) to standard output. The issue I am having is when the file has multiple lines being read. The first line is read and done properly but the other lines do not work correctly. For instance, the text file will contain this:

.......1.unsigne

...unsigned char

------------------------

and results in: 0000000: 2e2e 2e2e 2e2e 2e31 2e75 6e73 6967 6e65 .......1.unsigne

0000010: 0a00 0000 0000 0000 0000 0000 0000 0000 ................

but should result in: 0000000: 2e2e 2e2e 2e2e 2e31 2e75 6e73 6967 6e65 .......1.unsigne

0000010: 2e2e 2e75 6e73 6967 6e65 6420 6368 6172 ...unsigned char

Any ideas on how to fix this?

--------------------------------------------------------------------

CODE

--------------------------------------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE 1000

void hexDump (char *desc, void *addr, int len) {
int i;
unsigned char buffline[17];
unsigned char *pc = (unsigned char*)addr;
if(desc != NULL){
printf("%s: \n", desc);
}
for (i = 0; i < len; i++){
if ((i % 16) == 0){
if (i != 0)
printf(" %s\n", buffline);
if(pc[i] == 0x00) exit (0);
printf(" %07x: ", i); //prints address
}
printf ("%02x", pc[i]);
if ((i % 2) == 1)
printf(" ");
if ((pc[i] < 0x20) || (pc[i] > 0x7e)){ //non-printable chars
buffline[i % 16] = '.';
}
else{
buffline[i % 16] = pc[i];
}
buffline[(i % 16) + 1] = '\0'; //clear array
}
while ((i % 16) != 0) { //'.' fill last line
printf (" ");
i++;
}
printf (" %s\n", buffline);
}

int main (int argc, char *argv[]) {
FILE *fp;
char buff[SIZE];
fp = fopen(argv[1], "r");
memset(buff, '\0', sizeof(buff));
fgets(buff, SIZE, fp);
hexDump("buff", &buff, sizeof(buff));
fclose(fp);
return 0;
}

Answer 1

Note: Main problem was you were reading only one line and passing it to the hexDump function.

So I have added a loop. Now its reading both the lines. I have solved your main problem.

Now, There is need to modify your function because you have used a logic that you finds best,thats why I am not modifying the code otherwise whole program has to be modified.

Remember second line consists of non printable characters so modify accordingly.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define SIZE 1000

void hexDump(void * addr, int len) { // no need to pass desc message
int i;
unsigned char buffline[17];
unsigned char * pc = (unsigned char * ) addr;
/*if (desc != NULL) {
printf("%s: \n", desc); //removing this message you should add this is main
}*/
for (i = 0; i < len; i++) {
if ((i % 16) == 0) {
if (i != 0)
printf(" %s\n", buffline);
if (pc[i] == 0x00) {
return; //exit will end the program and you cant modify next line
}
printf(" %07x: ", i); //prints address
}
printf("%02x", pc[i]);
if ((i % 2) == 1)
printf(" ");
if ((pc[i] < 0x20) || (pc[i] > 0x7e)) { //non-printable chars
buffline[i % 16] = '_'; //changed to _ so that you can identity whether it is . or non printable char
} else {
buffline[i % 16] = pc[i];
}
buffline[(i % 16) + 1] = '\0'; //clear array
}
while ((i % 16) != 0) { //'.' fill last line
printf(" ");
i++;
}
printf(" %s\n", buffline);
}

int main(int argc, char * argv[]) {
FILE * fp;
char buff[SIZE];
int count=1;
fp = fopen("c:\\users\\faraz\\desktop\\a.txt", "r");
memset(buff, '\0', sizeof(buff));
while(fgets(buff, SIZE, fp)){ // added for reading multiple lines in a file
hexDump(& buff, sizeof(buff));
}
fclose(fp);
system("PAUSE");
return 0;
}