廢話不多說，先看下面一段代碼
#include <iostream>#include <map>using namespace std;class A{public:typedef std::map<int, string> myMap;void mapInsert(int i, string s){map.insert(std::make_pair(i, s));}void deleteMap(){for (myMap::iterator it = map.begin(); it != map.end(); ++it){map.erase(it->first);}}private:myMap map;};int main(){A a;a.mapInsert(1, "1");a.mapInsert(2, "2");a.mapInsert(3, "3");a.mapInsert(4, "4");a.mapInsert(5, "5");a.deleteMap();return 0;}上述代碼編譯運行皆沒有問題，但是用valgrind檢測會提示錯誤：
valgrind --tool=memcheck --leak-check=full --track-origins=yes ./test # ~/test==723953== Memcheck, a memory error detector==723953== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.==723953== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info==723953== Command: ./test==723953== ==723953== Invalid read of size 8==723953== at 0x3431C69E60: std::_Rb_tree_increment(std::_Rb_tree_node_base*) (tree.cc:60)==723953== by 0x40131C: std::_Rb_tree_iterator<std::pair<int const, std::string> >::operator++() (in /home/thm/test/test)==723953== by 0x40117C: A::deleteMap() (in /home/thm/test/test)==723953== by 0x400F4B: main (in /home/thm/test/test)==723953== Address 0x4c580b8 is 24 bytes inside a block of size 48 free'd==723953== at 0x4A06016: operator delete(void*) (vg_replace_malloc.c:480)==723953== by 0x401E23: __gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<int const, std::string> > >::deallocate(std::_Rb_tree_node<std::pair<int const, std::string> >*, unsigned long) (in /home/thm/test/test)==723953== by 0x401C99: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::_M_put_node(std::_Rb_tree_node<std::pair<int const, std::string> >*) (in /home/thm/test/test)==723953== by 0x401AA6: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::_M_destroy_node(std::_Rb_tree_node<std::pair<int const, std::string> >*) (in /home/thm/test/test)==723953== by 0x401729: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::erase(std::_Rb_tree_iterator<std::pair<int const, std::string> >) (in /home/thm/test/test)==723953== by 0x40134C: std::map<int, std::string, std::less<int>, std::allocator<std::pair<int const, std::string> > >::erase(std::_Rb_tree_iterator<std::pair<int const, std::string> >) (in /home/thm/test/test)==723953== by 0x401170: A::deleteMap() (in /home/thm/test/test)==723953== by 0x400F4B: main (in /home/thm/test/test)==723953== ==723953== Invalid read of size 8==723953== at 0x3431C69E80: std::_Rb_tree_increment(std::_Rb_tree_node_base*) (tree.cc:68)==723953== by 0x40131C: std::_Rb_tree_iterator<std::pair<int const, std::string> >::operator++() (in /home/thm/test/test)==723953== by 0x40117C: A::deleteMap() (in /home/thm/test/test)==723953== by 0x400F4B: main (in /home/thm/test/test)==723953== Address 0x4c580a8 is 8 bytes inside a block of size 48 free'd==723953== at 0x4A06016: operator delete(void*) (vg_replace_malloc.c:480)==723953== by 0x401E23: __gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<int const, std::string> > >::deallocate(std::_Rb_tree_node<std::pair<int const, std::string> >*, unsigned long) (in /home/thm/test/test)==723953== by 0x401C99: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::_M_put_node(std::_Rb_tree_node<std::pair<int const, std::string> >*) (in /home/thm/test/test)==723953== by 0x401AA6: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::_M_destroy_node(std::_Rb_tree_node<std::pair<int const, std::string> >*) (in /home/thm/test/test)==723953== by 0x401729: std::_Rb_tree<int, std::pair<int const, std::string>, std::_Select1st<std::pair<int const, std::string> >, std::less<int>, std::allocator<std::pair<int const, std::string> > >::erase(std::_Rb_tree_iterator<std::pair<int const, std::string> >) (in /home/thm/test/test)==723953== by 0x40134C: std::map<int, std::string, std::less<int>, std::allocator<std::pair<int const, std::string> > >::erase(std::_Rb_tree_iterator<std::pair<int const, std::string> >) (in /home/thm/test/test)==723953== by 0x401170: A::deleteMap() (in /home/thm/test/test)==723953== by 0x400F4B: main (in /home/thm/test/test)==723953== ==723953== ==723953== HEAP SUMMARY:==723953== in use at exit: 0 bytes in 0 blocks==723953== total heap usage: 10 allocs, 10 frees, 370 bytes allocated==723953== ==723953== All heap blocks were freed -- no leaks are possible==723953== ==723953== For counts of detected and suppressed errors, rerun with: -v==723953== ERROR SUMMARY: 8 errors from 2 contexts (suppressed: 6 from 6)
Why?
此代碼可以實現功能要求，但是健壯性并不好，假設在map.erase之后再次使用map當前的iterator，即
void deleteMap(){for (myMap::iterator it = map.begin(); it != map.end(); ++it){map.erase(it->first);std::cout << "map.first=" << it->first << " map.second=" << it->second << std::endl;}}代碼運行就會出現錯誤，因為it目前指向的對象已經被刪掉了。
為了避免程序出現這樣的錯誤，我們應該保證在iterator指向的對象被刪掉之前，iterator已經向前移位一。
程序改成如下即可：
void deleteMap(){for (myMap::iterator it = map.begin(); it != map.end();){map.erase(it++->first);}} 或
void deleteMap(){for (myMap::iterator it = map.begin(); it != map.end();){int i = it->first;++it;map.erase(i);}}以上所述是小編給大家介紹的for循環中刪除map中的元素valgrind檢測提示error：Invalid read of size 8 ，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對武林網網站的支持！
新聞熱點
疑難解答
圖片精選
