标准地图给出分段错误

Question

我在程序中使用 map 将稀疏矩阵转换为紧凑数组。

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
}

在处理了固定数量的 （100498277） 条目后，它给了我一个分段错误。

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; }

英国电信演出

#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

瓦尔格林德输出

==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还报告了地图其他功能中数据丢失的可能性该程序仅使用可用系统内存的10%。

请帮忙

Answer 1

您在访问 itr->second 之前没有初始化itr。事实上，你根本没有给itr赋予任何法律价值。