Nesting Debug Output

Keeping debug output readable when it is nested or split over several calls.

Calling functions inside Dout

Consider the following code:

int foobar() __attribute__ ((const));
 
int foobar()
{
  Dout(dc::notice, "Entering foobar()");
  Dout(dc::notice, "Leaving foobar()");
  return 1;
}
 
int main()
{
  Dout(dc::kernel, "The value of foobar() = " << foobar()
      << ", aint that nice?");
  return foobar();
}

This code would start a new debug message before the previous debug message is finished.  Libcwd detects this and will output:

NOTICE:     Entering foobar()
NOTICE:     Leaving foobar()
KERNEL: The value of foobar() = 2, aint that nice?

Note the indentation and the fact that the printing of the label KERNEL was delayed.

Using continued_cf, dc::continued and dc::finish

In the previous section foobar() was a const function: it didn't matter whether or not it was called for the functionality of the application. But when it does matter, then one might want to do something like this:

Dout(dc::kernel|flush_cf|continued_cf, "Generating tables... ");
generate_tables();
Dout(dc::finish, "done");

If generate_tables() would not print debug messages, then the output will look like:

KERNEL: Generating tables... done

When it does generated debug output, then the <unfinished> and <continued> labels are printed also:

KERNEL: Generating tables... <unfinished>
NOTICE:     Inside generate_tables()
KERNEL: <continued> done

Finally, it is also possible to split a debug line into more than two parts by using the special dc::continued debug channel.

Dout(dc::notice|flush_cf|continued_cf, "Generating tables.");
for (int i = 0; i < 8; ++i)
{
  generate_table(i);
  Dout(dc::continued, '.');
}
Dout(dc::finish, " done");

When generate_table(i) doesn't print debug messages, then the output will look like:

NOTICE: Generating tables......... done

When it does generate debug output, then each dot would be surrounded by a <continued> .<unfinished> :

NOTICE: Generating tables.<unfinished>
TABLE :     Inside generate_table(0)
NOTICE: <continued> .<unfinished>

etc.