Formatting a C Program - c

Question

So I have a program that takes a file and reads in character by character and prints the character and the hexadecimal equivalent.
`
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE *labFile;
char buf;
labFile = fopen("lab1.dat", "r");
if (labFile == NULL) perror("Error opening file\n");
while( (buf = fgetc(labFile) ) != EOF){
if(("%x", buf)< 16){
printf("%c 0%x\n", buf, buf);
}
else
printf("%c %x\n", buf, buf);
}
fclose(labFile);
return 0;
}
`
The program works the way I need it to except for one thing. I need the program to output the hex number on top then the character directly underneath the number and this process needs to continue horizontally.
Any help would be greatly appreciated!

Answer 1

You should output the characters as hex first, and save each read in character that has been printed until you run out of columns on your screen. You can then move to the next line, and print out the characters that were saved underneath the hex output.
You can simplify your logic to format your hex output into a single print statement.
When printing out the character, you need to have a plan to represent non-printable characters. In the sample program below, we handle it by printing two consecutive dots.
void print_chars (unsigned char *p, int num) {
int i;
for (i = 0; i < num; ++i) {
printf("%s%c%s",
isprint(p[i]) ? " " : ".",
isprint(p[i]) ? p[i] : '.',
(i < num-1) ? " " : "\n");
}
}
int main() {
FILE *labFile;
char buf;
int count = 0;
int num = COLUMNS/3;
char printed[num];
labFile = fopen("lab1.dat", "r");
if (labFile == NULL) perror("Error opening file\n");
while( (buf = fgetc(labFile) ) != EOF) {
printf("%s%02x", count ? " " : "", buf);
printed[count++] = buf;
if (count == num) {
count = 0;
putchar('\n');
print_chars(printed, num);
}
}
fclose(labFile);
if (count) {
putchar('\n');
print_chars(printed, count);
}
return 0;
}
The number of columns is divided by 3 since each character takes about 3 columns for output (2 hex characters, and a space). Retrieving the number of columns is system dependent, but you can just plug in 80 if you wish.

Answer 2

You could do something like this. ASSUMES your lines are < 100 chars long. Not safe.
#include <stdio.h>
#include <stdlib.h>
int main(){
FILE *labFile;
char buf[100];
labFile = fopen("lab1.dat", "r");
if (labFile == NULL) perror("Error opening file\n");
while(fgets(buf, 100, labFile)) {
if(rindex(buf, '\n')) *rindex(buf, '\n') = 0;
int i, n = strlen(buf);
for(i = 0; i != n; i++) {
printf("0%x ", buf[i]);
}
printf("\n");
for(i = 0; i != n; i++) {
printf("%c ", buf[i]);
}
printf("\n");
}
fclose(labFile);
return 0;
}