Where's the backtrace?

Ruby
1

I’m probably misunderstanding the way things are supposed to work.
Here’s what I’m seeing:

$ cat lib.rb
class MyClass
def throws_an_exception
self.non_existent_method
end
end

if FILE == $0
MyClass.new.throws_an_exception
end
$ ruby lib.rb
lib.rb:3:in throws_an_exception': undefined methodnon_existent_method’ for #MyClass:0x255bc (NoMethodError)
from lib.rb:8

So far, this is what I expect. Now consider:

$ cat the_test.rb
require ‘./lib’

begin
MyClass.new.throws_an_exception
rescue => e
puts e
end
$ ruby the_test.rb
undefined method `non_existent_method’ for #MyClass:0x2560c

I don’t get the rest of the backtrace (line number, etc.) unless I
use the -d flag:

$ ruby -d the_test.rb
Exception NoMethodError' at ./lib.rb:3 - undefined methodnon_existent_method’ for #MyClass:0x2560c
undefined method `non_existent_method’ for #MyClass:0x2560c

Is there a way to get the “full” backtrace when calling “the_test.rb”
without using the -d flag? I hope this makes sense.

Thanks,
Ryan

2

lists wrote:

if FILE == $0
require ‘./lib’
the -d flag:
Ryan

Check out the documentation for the Exception class:

http://ruby-doc.org/core/classes/Exception.html

There is a method for retrieving the backtrace. Try this:

begin
MyClass.new.throws_an_exception
rescue => e
puts e
puts e.backtrace.join(“\n”)
end

-Justin

3

On Jun 20, 2006, at 0:18, lists wrote:

I don’t get the rest of the backtrace (line number, etc.) unless I
use the -d flag:

$ ruby -d the_test.rb
Exception NoMethodError' at ./lib.rb:3 - undefined method non_existent_method’ for #MyClass:0x2560c
undefined method `non_existent_method’ for #MyClass:0x2560c

Is there a way to get the “full” backtrace when calling
“the_test.rb” without using the -d flag? I hope this makes sense.

The culprit is that you’re rescuing the exception, and simply
printing its name. To get the whole backtrace, you could not rescue
the exception in the first place, re-raise the exception, or print
the backtrace manually.

matthew smillie.

begin
MtClass.new.throws_an_exception
rescue => e
puts “oops, an exception”
raise e
end

begin
MyClass.new.throws_an_exception
rescue => e
puts e
puts e.backtrace
end

Relevant docs are:
Kernel#raise: module Kernel - RDoc Documentation
Exception#backtrace: http://ruby-doc.org/core/classes/
Exception.html#M001216

4

On Jun 19, 2006, at 6:36 PM, Matthew S. wrote:

puts e
puts e.backtrace
end

That’s what I was missing, thanks!

-Ryan