Segfault when adding item to std :: map
I have something strange when I try to insert one item into a map
main.cpp
S3Wrapper wrapper = S3Wrapper::getS3Wrapper();
int main(){
return 0;
}
So basically the only singleton is called for S3Wrapper
S3Wrapper.hpp
class S3Wrapper
{
S3Wrapper(std::string bucketName);
public:
~S3Wrapper();
static S3Wrapper &getS3Wrapper(std::string name = BUCKET_NAME);
}
and S3Wrapper.cpp
static std::map<std::string, S3Wrapper*> _wrapperMap;
S3Wrapper& S3Wrapper::getS3Wrapper(std::string name)
{
auto it = _wrapperMap.find(name);
if (it == _wrapperMap.end())
{
auto t = new S3Wrapper(name);
_wrapperMap[name] = t;
return *(_wrapperMap[name]);
}
return *(it->second);
}
When I compile, I don't have any errors / warnings, but then the program segfault:
g++ main.cpp S3Wrapper.cpp -std=c++0x -ls3 -g3
gdb result
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7937c4a in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
(gdb) bt
#0 0x00007ffff7937c4a in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#1 0x0000000000406295 in std::_Rb_tree_iterator<std::pair<std::string const, S3Wrapper*> >::operator-- (this=0x7fffffffd8b0) at /usr/include/c++/4.8/bits/stl_tree.h:204
#2 0x00000000004061f7 in std::_Rb_tree<std::string, std::pair<std::string const, S3Wrapper*>, std::_Select1st<std::pair<std::string const, S3Wrapper*> >, std::less<std::string>, std::allocator<std::pair<std::string const, S3Wrapper*> > >::_M_get_insert_unique_pos (this=0x60b580 <_wrapperMap>, __k=...) at /usr/include/c++/4.8/bits/stl_tree.h:1333
#3 0x00000000004058f5 in std::_Rb_tree<std::string, std::pair<std::string const, S3Wrapper*>, std::_Select1st<std::pair<std::string const, S3Wrapper*> >, std::less<std::string>, std::allocator<std::pair<std::string const, S3Wrapper*> > >::_M_get_insert_hint_unique_pos (this=0x60b580 <_wrapperMap>, __position=..., __k=...) at /usr/include/c++/4.8/bits/stl_tree.h:1425
#4 0x000000000040511c in std::_Rb_tree<std::string, std::pair<std::string const, S3Wrapper*>, std::_Select1st<std::pair<std::string const, S3Wrapper*> >, std::less<std::string>, std::allocator<std::pair<std::string const, S3Wrapper*> > >::_M_emplace_hint_unique<std::piecewise_construct_t const&, std::tuple<std::string const&>, std::tuple<> >(std::_Rb_tree_const_iterator<std::pair<std::string const, S3Wrapper*> >, std::piecewise_construct_t const&, std::tuple<std::string const&>&&, std::tuple<>&&) (this=0x60b580 <_wrapperMap>, __pos=...) at /usr/include/c++/4.8/bits/stl_tree.h:1673
#5 0x0000000000404d24 in std::map<std::string, S3Wrapper*, std::less<std::string>, std::allocator<std::pair<std::string const, S3Wrapper*> > >::operator[] (this=0x60b580 <_wrapperMap>, __k=...)
at /usr/include/c++/4.8/bits/stl_map.h:465
#6 0x0000000000404945 in S3Wrapper::getS3Wrapper (name=...) at S3Wrapper.cpp:55
#7 0x00000000004021e3 in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at main.cpp:8
#8 0x00000000004022ce in _GLOBAL__sub_I_wrapper () at main.cpp:41
#9 0x0000000000406b7d in __libc_csu_init ()
#10 0x00007ffff7308e55 in __libc_start_main (main=0x401edc <main()>, argc=1, argv=0x7fffffffdc28, init=0x406b30 <__libc_csu_init>, fini=<optimized out>, rtld_fini=<optimized out>,
stack_end=0x7fffffffdc18) at libc-start.c:246
#11 0x0000000000401b79 in _start ()
line55: _wrapperMap[name] = t;
If I insert t into a vector I have no problem
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This is a static initialization fiasco: static variables defined in different translation units are initialized in an unspecified order, so there is no guarantee that they are _wrapperMap
initialized before initialization is needed wrapper
.
The best solution is to avoid static / global variables. They usually only cause trouble.
If you really want global state, a safer option is to use a local static variable:
std::map<std::string, S3Wrapper*> & wrapperMap() {
static std::map<std::string, S3Wrapper*> map;
return map;
}
This is guaranteed to be initialized the first time the function is called, so there is no danger of using the map before initialization. You may have problems when static variables are destroyed at the end of the program.
Note that it is _wrapperMap
reserved (in the global namespace), so you must choose the name without the leading underscore, or put it in the namespace.
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