map中的key必须重载 "< " 运算符；map中value存放map类型时，不使用new：
1 #include <iostream> 2 #include <map> 3 #include <string> 4 5 using namespace std; 6 7 int main() 8 { 9 std::map<int, std::map<std::string, int>* > test_map; 10 std::map<std::string, int> map_01 ; 11 for(int i=0; i<10; ++i){ 12 //map_01 = new std::map<std::string, int>; 13 map_01.insert(make_pair("test_11", i)); #每次循环操作的是一个map,有点引用的意味 14 std::cout <<"map address " <<&map_01 << std::endl; 15 test_map.insert(make_pair(i, &map_01)); 16 } 17 18 for(std::map<int, std::map<std::string, int>* >::iterator it=test_map.begin(); it!=test_map.end(); ++it){ 19 std::cout << "first " << it->first << "map_address "<< it->second << std::endl; 20 } 21 22 /* 23 for(std::map<int, std::map<std::string, int>* >::iterator it = test_map.begin(); 24 it != test_map.end(); ++it){ 25 map_01 = it->second; 26 delete map_01; 27 map_01 = NULL; 28 } 29 */ 30 31 return 0; 32 }
运行结果：
1 root@u18:~/cp/test# g++ map2.cpp -g -Wall 2 root@u18:~/cp/test# valgrind --tool=memcheck --leak-check=yes ./a.out 3 ==19991== Memcheck, a memory error detector 4 ==19991== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al. 5 ==19991== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info 6 ==19991== Command: ./a.out 7 ==19991== 8 map address 0x7ff0003c0 9 map address 0x7ff0003c0 10 map address 0x7ff0003c0 11 map address 0x7ff0003c0 12 map address 0x7ff0003c0 13 map address 0x7ff0003c0 14 map address 0x7ff0003c0 15 map address 0x7ff0003c0 16 map address 0x7ff0003c0 17 map address 0x7ff0003c0 18 first 0map_address 0x7ff0003c0 19 first 1map_address 0x7ff0003c0 20 first 2map_address 0x7ff0003c0 21 first 3map_address 0x7ff0003c0 22 first 4map_address 0x7ff0003c0 23 first 5map_address 0x7ff0003c0 24 first 6map_address 0x7ff0003c0 25 first 7map_address 0x7ff0003c0 26 first 8map_address 0x7ff0003c0 27 first 9map_address 0x7ff0003c0 28 ==19991== 29 ==19991== HEAP SUMMARY: 30 ==19991== in use at exit: 0 bytes in 0 blocks 31 ==19991== total heap usage: 21 allocs, 21 frees, 848 bytes allocated 32 ==19991== 33 ==19991== All heap blocks were freed -- no leaks are possible 34 ==19991== 35 ==19991== For counts of detected and suppressed errors, rerun with: -v 36 ==19991== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
使用new map情况：
1 #include <iostream> 2 #include <map> 3 #include <string> 4 5 using namespace std; 6 7 int main() 8 { 9 std::map<int, std::map<std::string, int>* > test_map; 10 std::map<std::string, int>* map_01; 11 for(int i=0; i<10; ++i){ 12 map_01 = new std::map<std::string, int>; 13 std::cout <<"map address " <<map_01 << std::endl; 14 test_map.insert(make_pair(i, map_01)); 15 } 16 17 for(std::map<int, std::map<std::string, int>* >::iterator it=test_map.begin(); it!=test_map.end(); ++it){ 18 std::cout << "first " << it->first << "map_address "<< it->second << std::endl; 19 } 20 21 for(std::map<int, std::map<std::string, int>* >::iterator it = test_map.begin(); 22 it != test_map.end(); ++it){ 23 map_01 = it->second; 24 delete map_01; 25 map_01 = NULL; 26 } 27 28 return 0; 29 }
运行情况：
1 root@u18:~/cp/test# g++ map.cpp -g -Wall 2 root@u18:~/cp/test# valgrind --tool=memcheck --leak-check=yes ./a.out 3 ==19960== Memcheck, a memory error detector 4 ==19960== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al. 5 ==19960== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info 6 ==19960== Command: ./a.out 7 ==19960== 8 map address 0x5a02040 9 map address 0x5a02120 10 map address 0x5a02200 11 map address 0x5a022e0 12 map address 0x5a023c0 13 map address 0x5a024a0 14 map address 0x5a02580 15 map address 0x5a02660 16 map address 0x5a02740 17 map address 0x5a02820 18 first 0map_address 0x5a02040 19 first 1map_address 0x5a02120 20 first 2map_address 0x5a02200 21 first 3map_address 0x5a022e0 22 first 4map_address 0x5a023c0 23 first 5map_address 0x5a024a0 24 first 6map_address 0x5a02580 25 first 7map_address 0x5a02660 26 first 8map_address 0x5a02740 27 first 9map_address 0x5a02820 28 ==19960== 29 ==19960== HEAP SUMMARY: 30 ==19960== in use at exit: 0 bytes in 0 blocks 31 ==19960== total heap usage: 20 allocs, 20 frees, 960 bytes allocated 32 ==19960== 33 ==19960== All heap blocks were freed -- no leaks are possible 34 ==19960== 35 ==19960== For counts of detected and suppressed errors, rerun with: -v 36 ==19960== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
map的insert返回值：
1 map<string, int> word_count; 2 string word; 3 while(cin>>word){ 4 //map insert的返回值类型 5 pair<map<string, int>::iterator, bool> ret = 6 word_count.insert(make_pair(word, 1)); 7 if(!ret.second){ 8 ++ret.first->second; 9 } 10 } 11 12 //返回值为key为迭代器，value为bool值的map；插入成功与否由bool值来表示