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jean
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 Posted: Sat Aug 12, 2006 4:30 am Post subject: STL variable scope |
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Hi,
I have the following code(it may have syntax error), but ignore. Just
the idea. The question is:
1. Does customTagsEle get destroyed when func1() exit? It seems not.
But why not? local variable should be destroyed when it do out of
scope.
2.When does m_map get destroyed? Is it when CMyClass object get
destroyed?
3. When does the class A's object get destroyed?
Class A
{
....
}
class CMyClass
{
private:
std::map<std::string, boost::shared_ptr<A> > m_map;
public:
func1();
}
CMyClass::func1()
{
std::pair< std::string, boost::shared_ptr<A> > customTagsEle;
customTagsEle = std::make_pair( std::string((LPCTSTR)m_name),
boost::shared_ptr<A>( new A ) );
m_map.push_back( customTagsEle);
}
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Thomas Maeder
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| Posted: Sat Aug 12, 2006 4:58 pm Post subject: Re: STL variable scope |
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{ Extra blank lines (double-spacing) removed. Please don't post
double-spaced articles. It's probably the posting tool doing this
behind the scenes; let's hope my e-mail client doesn't <g>. -mod/aps }
"jean" <jean.shu (AT) gmail (DOT) com> writes:
[rearranged by tm]
| Quote: | Class A
{
....
}
class CMyClass
{
private:
std::map<std::string, boost::shared_ptr<A> > m_map;
public:
func1();
}
CMyClass::func1()
{
std::pair< std::string, boost::shared_ptr<A> > customTagsEle;
customTagsEle = std::make_pair( std::string((LPCTSTR)m_name),
boost::shared_ptr<A>( new A ) );
m_map.push_back( customTagsEle);
}
1. Does customTagsEle get destroyed when func1() exit?
|
Yes.
| Quote: | It seems not. But why not? local variable should be destroyed when
it do out of scope.
|
How do you come to the conclusion that it doesn't?
| Quote: | 2.When does m_map get destroyed? Is it when CMyClass object get
destroyed?
|
Yes.
| Quote: | 3. When does the class A's object get destroyed?
|
Please post a complete, compilable program if you want to get a
accurate answer.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Alex
Guest
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| Posted: Sat Aug 12, 2006 6:48 pm Post subject: Re: STL variable scope |
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{ Quoted clc++m banner removed. -mod/aps }
jean wrote:
| Quote: | 1. Does customTagsEle get destroyed when func1() exit? It seems not.
But why not? local variable should be destroyed when it do out of
scope.
|
customTagsEle does get destroyed. However, m_map contains a copy of it.
| Quote: | 2.When does m_map get destroyed? Is it when CMyClass object get
destroyed?
|
Yes.
| Quote: | 3. When does the class A's object get destroyed?
|
On m_map destruction.
| Quote: |
Class A
{
....
}
class CMyClass
{
private:
std::map<std::string, boost::shared_ptr<A> > m_map;
public:
func1();
}
CMyClass::func1()
{
std::pair< std::string, boost::shared_ptr<A> > customTagsEle;
customTagsEle = std::make_pair( std::string((LPCTSTR)m_name),
boost::shared_ptr<A>( new A ) );
m_map.push_back( customTagsEle);
}
|
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Vladimir Marko
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| Posted: Tue Aug 15, 2006 2:31 am Post subject: Re: STL variable scope |
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jean wrote:
| Quote: | std::pair< std::string, boost::shared_ptr<A> > customTagsEle;
customTagsEle = std::make_pair( std::string((LPCTSTR)m_name),
boost::shared_ptr<A>( new A ) );
|
I'd like to point out that this line is breaks the basic exception
safety guarantee. The compiler is free to choose the following
order of "function calls":
1. new A
2. construct std::string
3. construct boost::shared_ptr<.>
4. std::make_pair(.,.)
If the construction of std::string throws, the A object is leaked.
Regards,
Vladimir Marko
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