std :: set迭代器自动const [英] std::set iterator automatically const
问题描述
为简单起见,我已经提取了问题并更改了名称,等等。
I have extracted the problem and changed names and so for simplicities sake.
基本上我实例化一个类,然后将其存储在std :: set中,稍后我希望引用该类,以便我可以检查其值并对其进行修改...
Basically I instantiate a class and I stock it in a std::set, later on I'd like to have a reference to the class so that I can check its values and modify them...
简化代码:
MyClass tmpClass;
std::set<MyClass > setMyClass;
setMyClass.insert(tmpClass);
std::set<MyClass >::iterator iter;
iter=setMyClass.begin();
MyClass &tmpClass2=*iter;
和错误:
error C2440: 'initializing' : cannot convert from 'const MyClass' to 'MyClass &'
(我也删除了部分错误消息 MVB :: Run ::,也将其清除。)
(I removed parts of the error message, "MVB::Run::" to clear it up too.)
如果我添加前面的内容'const'到代码的最后一行,然后一切正常,但是我不能更改值...
if I add a preceding 'const' to the last line of code then everything works well but then I can't change the value...
这是正常现象,我必须说,删除数据,更改值,然后再放回去?
Is this normal behaviour and I have to, say, remove the data, change values and put it back again?
我感觉这与集合的排序有关,但是我不会碰
I have the feeling that this has something to do with the sorting of the set but I won't touch the variables that are used for the sorting.
推荐答案
我确定您不会碰到用于排序的变量
,您可以使用 const_cast 像这样:
I you are certain you won't touch the variables that are used for the sorting
the you could work around this by using a const_cast like this:
MyClass tmpClass;
std::set<MyClass > setMyClass;
setMyClass.insert(tmpClass);
std::set<MyClass >::iterator iter;
iter=setMyClass.begin();
const MyClass &tmpClass2=*iter;
MyClass &tmpClass3 = const_cast<MyClass&>(tmpClass2);
或者,您可以将要更改的类的成员声明为可变。
Alternatively, you could declare the members of the class that you intend to change as mutable.
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