Re: vector.erase(iterator iter) will change "iter" or not?
On Feb 22, 11:54 am, Richard Herring <junk@[127.0.0.1]> wrote:
In message
<c76ba343-355d-46ed-b028-3cd137425...@s13g2000prd.googlegroups.com>, Old
Wolf <oldw...@inspire.net.nz> writes
On Feb 22, 4:31 am, Richard Herring <junk@[127.0.0.1]> wrote:
In message <fpk2sg$5d...@news.datemas.de>, Victor Bazarov
The iterator that refers to the removed element and all
elements after the removed one are invalidated by that
operation. IOW, the Standard makes no attempt to define
what the 'iter' would point to after being erased.
I wonder if the OP is confused because the iterator is
passed by value and therefore not modified? Obviously
erase(iter) can't change its _value_, but it certainly
changes its _meaning_ - what it points to is no longer
valid.
The value certainly is changed: previously it was
well-defined and now it is indeterminate!
Its value has become singular, certainly, but that's because
the set of singular values has changed, not because the
iterator has.
It doesn't point anywhere; it's nonsensical to say that what
it points to is not valid.
If it doesn't point anywhere, it points nowhere. "nowhere"
looks pretty invalid to me.
It doesn't point, period.
Perhaps you mean to say that the representation isn't
changed;
Perhaps.
Consider:
#include <vector>
#include <cstring>
#include <iostream>
int
main()
{
static int const init[] = { 1, 2, 3, 4, 5 } ;
std::vector< int > v( init, init + 5 ) ;
std::vector< int >::iterator
iter = v.begin() + 3 ;
unsigned char before[ sizeof( iter ) ] ;
std::memcpy( before, &iter, sizeof( iter ) ) ;
v.erase( iter ) ;
if ( std::memcmp( before, &iter, sizeof( iter ) ) == 0 ) {
std::cout << "unchanged" << std::endl ;
} else {
std::cout << "changed" << std::endl ;
}
}
On my implementation, this outputs "changed". And any attempt
to access iter as an std::vector< int >::iterator (e.g. to copy
it, compare it, etc.) generates a core dump.
I don't quite know what you mean by "its representation". If
it's just the underlying bits in memory, then it's changed. If
it's anything else, then you can't tell, because there's nothing
you can do other than look at the bytes that has defined
behavior (and the implementation I normally use core dumps in
all of the cases of undefined behavior).
--
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