Exceptions/Catch an exception thrown in a nested call: Difference between revisions
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# Function foo should catch only exception U0, not U1. |
# Function foo should catch only exception U0, not U1. |
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Show/describe what happens when the program is run. |
Show/describe what happens when the program is run. |
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=={{header|Ada}}== |
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<lang ada>with Ada.Text_Io; use Ada.Text_Io; |
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procedure Exceptions_From_Nested_Calls is |
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U0 : exception; |
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U1 : exception; |
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Baz_Count : Natural := 0; |
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procedure Baz is |
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begin |
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Baz_Count := Baz_Count + 1; |
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if Baz_Count = 1 then |
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raise U0; |
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else |
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raise U1; |
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end if; |
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end Baz; |
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procedure Bar is |
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begin |
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Baz; |
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end Bar; |
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procedure Foo is |
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begin |
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Bar; |
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exception |
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when U0 => |
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Put_Line("Procedure Foo caught exception U0"); |
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end Foo; |
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begin |
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for I in 1..2 loop |
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Foo; |
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end loop; |
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exception |
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when U1 => |
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Put_line("Exception U1 passed through foo"); |
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end Exceptions_From_Nested_Calls;</lang> |
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Sample output: |
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<pre> |
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Procedure Foo caught exception U0 |
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Exception U1 passed through foo</pre> |
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=={{header|OCaml}}== |
=={{header|OCaml}}== |
Revision as of 03:00, 15 March 2009
You are encouraged to solve this task according to the task description, using any language you may know.
Show how to create a user-defined exception and show how to catch an exception raised from several nested calls away.
- Create two user-defined exceptions, U0 and U1.
- Have function foo call function bar which then calls function baz.
- Arrange for function baz to raise, or throw exception U0 on its first call, then exception U1 on its second.
- Function foo should catch only exception U0, not U1.
Show/describe what happens when the program is run.
Ada
<lang ada>with Ada.Text_Io; use Ada.Text_Io;
procedure Exceptions_From_Nested_Calls is
U0 : exception; U1 : exception; Baz_Count : Natural := 0; procedure Baz is begin Baz_Count := Baz_Count + 1; if Baz_Count = 1 then raise U0; else raise U1; end if; end Baz; procedure Bar is begin Baz; end Bar; procedure Foo is begin Bar; exception when U0 => Put_Line("Procedure Foo caught exception U0"); end Foo;
begin
for I in 1..2 loop Foo; end loop;
exception
when U1 => Put_line("Exception U1 passed through foo");
end Exceptions_From_Nested_Calls;</lang> Sample output:
Procedure Foo caught exception U0 Exception U1 passed through foo
OCaml
<lang ocaml>exception U0 exception U1
let baz i =
raise (if i = 0 then U0 else U1)
let bar i = baz i (* Nest those calls *)
let foo () =
for i = 0 to 1 do try bar i with U0 -> print_endline "Function foo caught exception U0" done
let () = foo ()</lang> Sample output:
Function foo caught exception U0 Exception: U1.
Python
There is no extra syntax to add to functions and/or methods such as bar, to say what exceptions they may raise or pass through them: <lang python>class U0(Exception): pass class U1(Exception): pass
def foo():
for i in range(2): try: bar(i) except U0: print "Function foo caught exception U0"
def bar(i):
baz(i) # Nest those calls
def baz(i):
raise U1 if i else U0
foo()</lang> Sample output:
Function foo caught exception U0 Traceback (most recent call last): File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 17, in <module> foo() File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 7, in foo bar(i) File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 12, in bar baz(i) # Nest those calls File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 15, in baz raise U1 if i else U0 U1
The first line of the output is generated from catching the U0 exception in function foo.
Uncaught exceptions give information showing where the exception originated through the nested function calls together with the name of the uncaught exception, (U1) to stderr, then quit the running program.