Civilized Programming Language

Code worked and stopped working after minor changes. All of the sudden a loop is not working anymore.

 1     while(cursor != NULL)
 2     {
 3         printk("mock_config_cache: checking %x\n", cursor);
 4         if (mock_compare_cache_devices((mock_cache_device_t*)cursor, new_cdev))
 5         {
 6             printk("mock_config_cache: Device already exists: %x\n", cursor);
 7             status = IOCMD_ERR_DEV_EXISTS;
 8             mock_free(new_cdev);
 9             break;
10         }
11 
12         cursor = cursor->next;
13 
14         if (cursor == cache_devices);
15         {
16             break;
17         }
18     }
19 

It should be easy, but this is a kernel code, so I’ve spent 1.5 hours to debug this code. Even if it weren’t a kernel code, it is not always easy to attach a debugger and step through the code. I’ve added a loop to print the linked list, which is basically the same code:

 1 /* DEB */
 2     cursor = cache_devices;
 3     while(cursor != NULL)
 4     {
 5         printk("Cursor: (%x), next: (%x), prev: (%x)\n", cursor, cursor->next, cursor->prev);
 6         cursor = cursor->next;
 7         if (cursor == cache_devices)
 8             break;
 9     }
10 

The same code, but this one is working!

Another coffee and I see the bug. Line #13 in the first code:

1        if (cursor == cache_devices);

Notice the “;” at the end of the line! DAMN! This is frustrating!

Now, the compiler should have told me something, as the IF statement does not even have a side-effects!

These days I have read an article by Andrei Alexandrescu (C++ template guru) called: “The case for D”, where he praised D language as a better C/C++. Naturally, I wondered if D would do better in the above bug:

 1 import std.stdio;
 2 
 3 void main()
 4 {
 5     writeln("hello world");
 6 
 7     int i=3;
 8     if (i == 3);
 9     {
10         writeln("another hello");
11     }
12 }

OK. Let’s see:

C:\Users\derbep\Documents\Code\DTest>dmd if_test.d




if_test.d(8): use '{ }' for an empty statement, not a ';'

Much much better! Advance to D! It is better!