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loose AT astron DOT nl
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 Posted: Wed May 09, 2007 3:11 pm Post subject: What's wrong with this code? |
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Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
<code>
#include <map>
#include <string>
#include <iostream>
using namespace std;
class Init
{
public:
Init();
private:
static map<int, string> map_;
static Init init_;
};
Init::Init()
{
map_[1] = "One"; // <--- Segfault here
}
Init Init::init_;
map<int, string> Init::map_;
int main()
{
return 0;
}
</code>
Kind regards,
Marcel Loose.
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Vladimir Marko
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| Posted: Wed May 09, 2007 7:39 pm Post subject: Re: What's wrong with this code? |
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On 9 May, 16:11, loose AT astron DOT nl <l...@astron.nl> wrote:
| Quote: | Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
code
#include <map
#include <string
#include <iostream
using namespace std;
class Init
{
public:
Init();
private:
static map<int, string> map_;
static Init init_;
};
Init::Init()
{
map_[1] = "One"; // <--- Segfault here
}
Init Init::init_;
map<int, string> Init::map_;
int main()
{
return 0;}
/code
|
The offending line is trying to use Init::map_ before it was
constructed. Init::init_ is guaranteed to be constructed
before Init::map_ because it's defined earlier in the same
translation unit. If you change the definition order, it
should work. It's a little fragile, however, and there are
better ways of constructing singletons. Try google :)
Regards,
Vladimir Marko
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Jens Kilian
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| Posted: Wed May 09, 2007 7:41 pm Post subject: Re: What's wrong with this code? |
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loose AT astron DOT nl <loose (AT) astron (DOT) nl> writes:
| Quote: | Could anyone tell me what's wrong with the code below?
|
The constructor for init_ is called before the one for map_.
Swap the following lines:
| Quote: | Init Init::init_;
map<int, string> Init::map_;
|
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Guest
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| Posted: Wed May 09, 2007 7:44 pm Post subject: Re: What's wrong with this code? |
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|
Hi Marcel,
Your problem lies in the order in which the static objects are
created. Since map_ is static and so is init_, your segfault probably
comes from the fact that init_ is created first, and so accesses map_,
which is scheduled to be created once Init() is finished.
To the others: there is no rule for the initialization of static
objects between modules, but how about statics in a same module? From
the example, I would guess that they are created in the order in which
they are defined, not declared. But is that specified?
Cheers,
Carl
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red floyd
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| Posted: Wed May 09, 2007 8:15 pm Post subject: Re: What's wrong with this code? |
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loose AT astron DOT nl wrote:
| Quote: | Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
|
Possibly the static initialization fiasco? Try swapping the lines
marked A and B below.
| Quote: |
code
#include <map
#include <string
#include <iostream
using namespace std;
class Init
{
public:
Init();
private:
static map<int, string> map_;
static Init init_;
};
Init::Init()
{
map_[1] = "One"; // <--- Segfault here
}
LINE A
Init Init::init_;
LINE B
map<int, string> Init::map_;
int main()
{
return 0;
}
/code
Kind regards,
Marcel Loose.
|
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Alberto
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| Posted: Wed May 09, 2007 8:15 pm Post subject: Re: What's wrong with this code? |
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On 9 Mag, 17:11, loose AT astron DOT nl <l...@astron.nl> wrote:
| Quote: | map_[1] = "One"; // <--- Segfault here
map_ is not an object during this segfault |
| Quote: | Init Init::init_; // Segfault here
map<int, string> Init::map_; // Life of map begin here
|
Change to:
map<int, string> Init::map_; // Life of map begin here
Init Init::init_; // Hopefully ok
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Martin Vuille
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| Posted: Wed May 09, 2007 8:15 pm Post subject: Re: What's wrong with this code? |
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loose AT astron DOT nl <loose (AT) astron (DOT) nl> wrote in
news:1178705110.137632.63970 (AT) w5g2000hsg (DOT) googlegroups.com:
| Quote: |
class Init
{
public:
Init();
private:
static map<int, string> map_;
static Init init_;
};
Init::Init()
{
map_[1] = "One"; // <--- Segfault here
}
Init Init::init_;
map<int, string> Init::map_;
|
These objects are initialized in order of declaration.
Since the Init c'tor uses the map, the map must be
declared first so that it will be initialized before
first use.
MV
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Bob Hairgrove
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| Posted: Wed May 09, 2007 8:16 pm Post subject: Re: What's wrong with this code? |
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{ Edits: double-spacing removed. -mod }
On Wed, 9 May 2007 09:11:02 CST, loose AT astron DOT nl
<loose (AT) astron (DOT) nl>
wrote:
| Quote: | Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
|
[snip]
| Quote: | Init Init::init_;
map<int, string> Init::map_;
[snip] |
Since these are in the same translation unit, they are initialized in
the order in which they are defined (see section 3.6.2 of the C++
standard). Switch the order of these lines and it works OK.
--
Bob Hairgrove
NoSpamPlease (AT) Home (DOT) com
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Kasimir
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| Posted: Wed May 09, 2007 8:17 pm Post subject: Re: What's wrong with this code? |
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On 9 Mai, 17:11, loose AT astron DOT nl <l...@astron.nl> wrote:
| Quote: | Hi,
Could anyone tell me what's wrong with the code below?
|
Hi Marcel,
the order of initialisation of static data members depends only from
the order of their definitions.
You have to switch the definitions of Init::init_ and Init::map_:
map<int, string> Init::map_;
Init Init::init_;
K.
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Salt_Peter
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| Posted: Wed May 09, 2007 8:17 pm Post subject: Re: What's wrong with this code? |
|
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On May 9, 11:11 am, loose AT astron DOT nl <l...@astron.nl> wrote:
| Quote: | Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
|
There is no map - yet.
| Quote: |
code
#include <map
#include <string
#include <iostream
using namespace std;
class Init
{
public:
Init();
private:
static map<int, string> map_;
static Init init_;
};
Init::Init()
{
map_[1] = "One"; // <--- Segfault here
}
Init Init::init_;
|
The above invokes Init's ctor before the static map comes to life.
try switching these two statements.
After all, isn't it natural that the members of a type be constructed
first?
| Quote: | map<int, string> Init::map_;
int main()
{
return 0;}
/code
Kind regards,
Marcel Loose.
|
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Bob Hairgrove
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| Posted: Wed May 09, 2007 11:39 pm Post subject: Re: What's wrong with this code? |
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{ Double-spacing corrected. -mod }
On Wed, 9 May 2007 13:44:01 CST, carl.seleborg (AT) gmail (DOT) com wrote:
| Quote: | ...is that specified?
Yes: see section 3.6.2 of the standard. |
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Seungbeom Kim
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| Posted: Thu May 10, 2007 1:07 am Post subject: Re: What's wrong with this code? |
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red floyd wrote:
| Quote: | loose AT astron DOT nl wrote:
Hi,
Could anyone tell me what's wrong with the code below? It segfaults
when the first element is being inserted in the map.
Possibly the static initialization fiasco? Try swapping the lines
marked A and B below.
|
It just occurs to me that the term "static initialization fiasco"
is misleading: because it doesn't have anything to do with
"static initialization", but only with "dynamic initialization".
It's true that it happens with static member objects, but non-member
objects suffer from the same phenomenon; the word "static" here probably
came from "static storage duration".
3.6.2/1: "Objects with *static storage duration* defined in namespace
scope in the same translation unit and *dynamically initialized* shall
be initialized in the order in which their definition appears in the
translation unit." (emphasis mine)
--
Seungbeom Kim
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Seungbeom Kim
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| Posted: Thu May 10, 2007 1:12 am Post subject: Re: What's wrong with this code? |
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|
Martin Vuille wrote:
| Quote: | loose AT astron DOT nl <loose (AT) astron (DOT) nl> wrote in
news:1178705110.137632.63970 (AT) w5g2000hsg (DOT) googlegroups.com:
Init Init::init_;
map<int, string> Init::map_;
These objects are initialized in order of declaration.
|
Not in order of declaration, but in order of definition.
| Quote: | Since the Init c'tor uses the map, the map must be
declared first so that it will be initialized before
first use.
|
The map must be "defined" first.
--
Seungbeom Kim
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