CODEWITHSUNDEEP
c++dictionarysegmentation-faultstd
siddhu323
siddhu323

Reputation: 104

Std Map giving Segmentation fault

I am using map in a program to convert a sparse matrix into a compact array.

map<int, int>  m_mCustIds;
map<int, int>::iterator itr;

 for (i=0; i<m_nRatingCount; i++)
{   
Data* rating = m_aRatings + i;
itr = m_mCustIds.find(rating->CustId); 
if (itr == m_mCustIds.end())
    {
        cid = 1 + (int)m_mCustIds.size();
    }
    else
    {
        cid = itr->second;
    }
// using cid in other data structures
}

After processing a fixed number (100498277) of entries it gives me a segmentation fault.

GDB Output
Program received signal SIGSEGV, Segmentation fault.
0x0000000000401ea0 in std::less<int>::operator() (this=0x2aab0adf5ed8, __x=@0x22, __y=@0x2aab0a80f0a4)
    at /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_function.h:227
227           { return __x < __y; }

bt shows

#0  0x0000000000401ea0 in std::less<int>::operator() (this=0x2aab0adf5ed8, __x=@0x22, __y=@0x2aab0a80f0a4)
    at /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_function.h:227
#1  0x000000000040218f in std::_Rb_tree<int, std::pair<int const, int>, std::_Select1st<std::pair<int const, int> >, std::less<int>, std::allocator<std::pair<int const, int> > >::find (this=0x2aab0adf5ed8, __k=@0x2aab0a80f0a4) at /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_tree.h:1317
#2  0x0000000000402243 in std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > >::find (this=0x2aab0adf5ed8, __x=@0x2aab0a80f0a4)
    at /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_map.h:534
#3  0x0000000000401b18 in Engine::CalcMetrics (this=0x2aaaaaad9010) at At.cpp:204
#4  0x0000000000401da3 in main () at At.cpp:141

Valgrind output

==18544== Invalid read of size 4
==18544==    at 0x401EA0: std::less<int>::operator()(int const&, int const&) const (stl_function.h:227)
==18544==    by 0x40218E: std::_Rb_tree<int, std::pair<int const, int>, std::_Select1st<std::pair<int const, int> >, std::less<int>, std::allocator<std::pair<int const, int> > >::find(int const&) (stl_tree.h:1317)
==18544==    by 0x402242: std::map<int, int, std::less<int>, std::allocator<std::pair<int const, int> > >::find(int const&) (stl_map.h:534)
==18544==    by 0x401B17: Engine::CalcMetrics() (At.cpp:204)
==18544==    by 0x401DA2: main (At.cpp:141)
==18544==  Address 0x22 is not stack'd, malloc'd or (recently) free'd

Valgrind also reports possilbe loss of data in other functions of map The program uses only 10 % of the available system memory.

Please help

Upvotes: 0

Views: 4236

Answers (1)

timrau
timrau

Reputation: 23058

You did not initialize itr before accessing itr->second. Indeed, you did not assign any legal value to itr at all.

Upvotes: 2

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