Hi,
i heard a lot about "undefined behaviour" in this and other newsgroups
dealing with c/c++.
Is there a list where all cases with undefined behaviour in C++ are listed?
regards marbac
48  3082 
"marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... Hi,
i heard a lot about "undefined behaviour" in this and other newsgroups
dealing with c/c++.
Is there a list where all cases with undefined behaviour in C++ are
listed?
I don't know of any compiled as a list.
But read the Holy Standard, it speaks a lot about undefined behaviors.
-Sharad
"marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... Hi,
i heard a lot about "undefined behaviour" in this and other newsgroups
dealing with c/c++.
Is there a list where all cases with undefined behaviour in C++ are
listed?
regards marbac
It's called the C++ standard, and its several hundred pages long.
Off the top of my head here are a few common causes of undefined behaviour
1) dereferencing a null pointer
2) accessing outside the bounds of an array
3) deleting the same memory twice
4) dereferencing a pointer after it has been deleted
5) dereferencing a pointer which points to a destroyed object
6) accessing an uninitialised variable
7) signed integer overflow
8) modifying a const object
No doubt I've missed many others
As you can see several of the common causes of undefined behaviour involve
pointers. So the moral is don't use pointers, prefer STL classes instead,
they are somewhat safer.
john
"John Harrison" <jo************ *@hotmail.com> wrote in message
news:2l******** ****@uni-berlin.de...
"marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... Hi,
i heard a lot about "undefined behaviour" in this and other newsgroups
dealing with c/c++.
Is there a list where all cases with undefined behaviour in C++ are
listed?
regards marbac
It's called the C++ standard, and its several hundred pages long.
Off the top of my head here are a few common causes of undefined behaviour
1) dereferencing a null pointer
2) accessing outside the bounds of an array
3) deleting the same memory twice
4) dereferencing a pointer after it has been deleted
5) dereferencing a pointer which points to a destroyed object
6) accessing an uninitialised variable
7) signed integer overflow
8) modifying a const object
Some more strike me -
1) main returning void
2) Copying a pointer after it has been deleted
3) Using mismatched forms of new/delete for arrays
4) Modifying a string literal
5) Changing a variable twice without a sequence point
6) Instantiating an STL container with auto_ptr
7) Adding declarations/definitions to std namespace
8) Playing around with reinterpret_cas t
many more...
-Sharad
"John Harrison" <jo************ *@hotmail.com> wrote in message
news:2l******** ****@uni-berlin.de... "marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... Is there a list where all cases with undefined behaviour in C++ are
listed?
.... Off the top of my head here are a few common causes of undefined behaviour
.... 1) dereferencing a null pointer
or any pointer to an address that has not been properly obtained ( i.e.
*(int*)454 = 0; ) 2) accessing outside the bounds of an array
3) deleting the same memory twice
or calling delete on an object addresss that was not allocated with
new.
3b) Using delete[] to release memory allocated with new,
or delete on the address returned by new[]. 4) dereferencing a pointer after it has been deleted
5) dereferencing a pointer which points to a destroyed object
6) accessing an uninitialised variable
or a variable that has been destroyed.
(NB: this also applies to global variables). 7) signed integer overflow
8) modifying a const object
Two important additions I can think of:
9) modifying a variable twice between sequence points (or accessing the
value being modified).
e.g. a = ++i + ++i; or a = i + ++i;
10) deleting a derived class through a pointer to a base class whose
destructor is not virtual.
Off the top of my head too, I think that these would be the most common
causes, but I'm sure the list can be extended.
Furthermore, UB may be triggered by causing library functions
to perform one of the above actions, for example by passing an
insufficiently large or invalid output buffer to functions such as sprintf
or strcpy.
Some standard library functions have explicit restrictions on the parameters
they
can receive (e.g. calling memcpy with overlapping memory ranges).
So it is important, for writing correct code, to understand the behavior
and restrictions of the functions you are calling. And it's not an obvious
thing.
No doubt I've missed many others
So do I...
The each of the C and C++ standards use the term "Undefined behavior"
close to 200 times, and an exaustive list is impossible to provide.
As you can see several of the common causes of undefined behaviour involve
pointers. So the moral is don't use pointers, prefer STL classes instead,
they are somewhat safer.
Overall, the C++ standard library does a better job than C's at trying to
prevent UB. What helps even more is if you are using an STL implementation
that
supports a 'debug' mode where all container iterators are checked at
runtime.
Some caveats I can think of include:
- initializing an std::string will a NULL char pointer.
- using [..] on standard containers (i.e. vector) does not verify range.
( vector::at() may be used instead, and will throw an exception ).
That's just adding my two cents, obviously my list is also partial and
incomplete...
Ivan
-- http://ivan.vecerina.com/contact/?subject=NG_POST <- e-mail contact form
"Ivan Vecerina" <NO************ *************** *******@vecerin a.com> skrev i
en meddelelse news:cd******** **@newshispeed. ch...
[snip] Some caveats I can think of include:
- initializing an std::string will a NULL char pointer.
- using [..] on standard containers (i.e. vector) does not verify range.
( vector::at() may be used instead, and will throw an exception ).
To be pedantic, nothing prevents vector::operato r[] to be implemented as
vector::at. At least this is how I read the standard.
No doubt most libraries will not do so for performance reasons, of course.
/Peter
That's just adding my two cents, obviously my list is also partial and
incomplete...
Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- e-mail contact form
Sharad Kala wrote:
"John Harrison" <jo************ *@hotmail.com> wrote in message
news:2l******** ****@uni-berlin.de...
"marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... > Hi,
>
> i heard a lot about "undefined behaviour" in this and other
> newsgroups dealing with c/c++.
>
> Is there a list where all cases with undefined behaviour in C++ are listed? >
> regards marbac
It's called the C++ standard, and its several hundred pages long.
Off the top of my head here are a few common causes of undefined
behaviour
1) dereferencing a null pointer
2) accessing outside the bounds of an array
3) deleting the same memory twice
4) dereferencing a pointer after it has been deleted
5) dereferencing a pointer which points to a destroyed object
6) accessing an uninitialised variable
7) signed integer overflow
8) modifying a const object
Some more strike me -
1) main returning void
2) Copying a pointer after it has been deleted
You could just combine a lot of the pointer stuff to:
Using the value of a pointer that doesn't point to a valid object.
3) Using mismatched forms of new/delete for arrays
4) Modifying a string literal
5) Changing a variable twice without a sequence point
Or changing and reading it
6) Instantiating an STL container with auto_ptr
7) Adding declarations/definitions to std namespace
8) Playing around with reinterpret_cas t
many more...
1) Dividing by zero
2) Pointer arithmetic that crosses array bounds
3) Returning a reference or pointer to a local variable
4) Writing to a member of a union and then reading another one
5) Deleting a derived class object though a pointer to a base class that
has no virtual destructor
7) Using offsetof on a non-POD class/struct
8) Using a map/set with a comparison function with no strict/weak
ordering for the key type
9) Accessing vector members that don't exist
10)Using a container iterator after it has become invalid
On Tue, 13 Jul 2004 14:11:18 +0200, "Peter Koch Larsen"
<pk*****@mailme .dk> wrote:
"Ivan Vecerina" <NO************ *************** *******@vecerin a.com> skrev i
en meddelelse news:cd******** **@newshispeed. ch...
[snip]
Some caveats I can think of include:
- initializing an std::string will a NULL char pointer.
- using [..] on standard containers (i.e. vector) does not verify range.
( vector::at() may be used instead, and will throw an exception ).
To be pedantic, nothing prevents vector::operato r[] to be implemented as
vector::at. At least this is how I read the standard.
No doubt most libraries will not do so for performance reasons, of course.
I wouldn't like a library that implemented operator[] as at. I don't
want exceptions from undefined behaviour, since the throwing context
is lost.
IMHO, any decent operator[] should at the very least have an assert in
it.
Tom
"marbac" <ma****@chello. at> wrote in message
news:qh******** **********@news .chello.at... Hi,
i heard a lot about "undefined behaviour" in this and other newsgroups
dealing with c/c++.
Is there a list where all cases with undefined behaviour in C++ are
listed?
regards marbac
I don't think it's really possible to compile a list. Think about it this
way: everything you could possibly do wrong that your compiler won't catch
is undefined behavior. Hence, what you're asking for is really a
compilation of all errors which could possibly be made in writing code,
which, unfortunately, is unlikely to exist anywhere, and would probably be
useless to you even if it did.
>Writing to a member of a union and then reading another one
Are you sure?
Certainly it seems as though it is a logic error which could possibly result in
undefined behavior, but is it guaranteed undefined behavior?
<CODE>
union FooBar
{
int Foo;
char Bar;
};
int main()
{
FooBar fooBar;
fooBar.Foo = 32; //Write FooBar::Foo
char bar = fooBar.Bar; //Oops! Read FooBar::Bar
return 0;
}
</CODE>
This code could results in the "rewrite your harddrive and sleep with your
girlfriend" kind of undefined behavior?
For that to happen wouldn't the compiler have to keep track of the last member
written to for each instance of a union so that it would be able to recognize
mismatched reads?
Just curious.
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