std :: string in struct - 复制/赋值问题？ [英] std::string in struct - Copy/assignment issues?

问题描述

假设我有一个包含std :: string的结构，如下所示：

Suppose I have a struct containing a std::string, like this:

struct userdata{
        int uid;
        std::string username;
    }

我需要创建一个复制的ctor或任何东西，或者在STL容器中使用它？考虑这个函数：

Do I need to create a copy ctor or anything to return it from a function or to use it inside a STL container? Consider this function:

userdata SomeClass::GetUserData(unsigned int uid)
{
    //do error checking and other stuff...
    //m_usermap is std::map<unsigned int, userdata>
    return m_usermap[uid];
}

当我将userdata结构体插入std :: map时， struct被创建，对吧？是否使用username字段的值创建了一个新的std :: string，或者做某种按位复制（这将是坏的）？类似地，当我从GetUserData方法返回一个userdata结构时，它是否有一个独立的字符串保存用户名或者我需要定义一个复制ctor并显式创建一个新的字符串？

When I insert userdata structs into the std::map, a copy of the struct gets created, right? Does a new std::string get created using the value of the username field, or does some sort of bitwise copy happen (this would be bad)? Similarly, when I return a userdata struct from the GetUserData method, does it have an independent string holding the username or do I need to define a copy ctor and explicitly create a new string?

推荐答案

std :: string 是引用计数，并且其复制构造函数发生。所以没有什么可担心的。一切都得到正确处理。

std::string is reference-counted, and its copy constructor takes place. So nothing to worry about. Everything is handled correctly.

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