ASCII printing

hex.c

@@ -1,10 +1,12 @@
 #include <stdio.h>
+#include <ctype.h>
 
 // TODO: ASCII/Position printing 
 // TODO: Stop appending garbage at file end
+// TODO: Simplify/clean some code (useless condition/loop guard brackets)
 
 #define BYTES 1024
-#define BYTES_PER_LINE 10
+#define BYTES_PER_LINE 20
 
 void print_hex(unsigned char* buf, int byteno)
 { 
@@ -12,10 +14,46 @@ void print_hex(unsigned char* buf, int byteno)
   {
     if (i % BYTES_PER_LINE == 0)
     {
+      if (i != 0)
+      {
+        printf("  ");
+        for (int j=i-BYTES_PER_LINE; j<i; j++)
+        {
+          if (isprint(buf[j])) 
+          {
+            printf("%c", buf[j]);
+          }
+          else {
+            printf(".");    
+          }
+        }
+      }
       puts("");
     }
     printf("%.2X ", buf[i]);
   }
+
+  // ASCII: last line 
+  int padding = BYTES_PER_LINE - (byteno % BYTES_PER_LINE);
+  if (padding < BYTES_PER_LINE)
+  {
+    for (int i=0; i<padding; i++)
+    {
+      printf("   ");
+    }
+    printf("  ");
+  }
+
+  int start = byteno - (byteno % BYTES_PER_LINE);
+  for (int j = start; j < byteno; j++) {
+    if (isprint(buf[j])) {
+      printf("%c", buf[j]);
+    }
+    else {
+      printf(".");
+    }
+  }
+
   puts("");
 }
 
@@ -35,7 +73,7 @@ int main(int argc, char** argv)
   for (;;)
   {
     char cmd;
-    int loc;
+    int loc = 0;
     scanf("%c%d", &cmd, &loc);
     switch(cmd)
     {
@@ -51,6 +89,10 @@ int main(int argc, char** argv)
       case 'S':
         fclose(f);
         f = fopen(argv[1], "w");
+        if (!f) {
+          perror("Error opening file for writing");
+          return -1;
+        }
         fwrite(buf, 1, BYTES, f);
         fclose(f);
         break;