索引和插入调用之间的 std::map 区别 [英] std::map difference between index and insert calls

问题描述

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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