索引和插入调用之间的 std::map 区别
索引重载运算符和std::map的insert方法调用有什么区别?
What is the difference between the index overloaded operator and the insert method call for std::map?
即:
some_map["x"] = 500;
对比
some_map.insert(pair<std::string, int>("x", 500));
推荐答案
相信insert()不会覆盖已经存在的值，可以通过测试返回的iterator/pair值中的bool值来检查操作结果
I believe insert() will not overwrite an existing value, and the result of the operation can be checked by testing the bool value in the iterator/pair value returned
对下标运算符 [] 的赋值只会覆盖那里的任何内容(如果那里还没有，则插入一个条目)
The assignment to the subscript operator [] just overwrites whatever's there (inserting an entry if there isn't one there already)
如果您没有预料到这种行为并且不适应这种行为，那么插入和 [] 运算符中的任何一个都可能导致问题.
Either of the insert and [] operators can cause issues if you're not expecting that behaviour and don't accommodate for it.
例如插入:
std::map< int, std::string* > intMap;
std::string* s1 = new std::string;
std::string* s2 = new std::string;
intMap.insert( std::make_pair( 100, s1 ) ); // inserted
intMap.insert( std::make_pair( 100, s2 ) ); // fails, s2 not in map, could leak if not tidied up
and with [] 运算符:
and with [] operator:
std::map< int, std::string* > intMap;
std::string* s1 = new std::string;
std::string* s2 = new std::string;
intMap[ 100 ] = s1; // inserted
intMap[ 100 ] = s2; // inserted, s1 now dropped from map, could leak if not tidied up
我认为这些是正确的，但没有编译它们，所以可能有语法错误
I think those are correct, but haven't compiled them, so may have syntax errors
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