将MFC CMap用于CString int对 [英] using MFC CMap for CString int pairs

问题描述

我当前正在处理一个DLL，该DLL需要在值的友好名称和值本身之间来回转换.由于该代码在整个代码库中的许多地方都使用过，因此我想尝试使其保持简单并在单个函数或对象中使用，因此我只需要声明一次即可.

I'm currently working on a DLL that needs to convert back and forth between the friendly name for a value and the value itself. As this code is used in many places throughout the codebase, I want to try and keep it simple and in a single function or object so I only have to declare them once.

从我的阅读看来，CMap是完成这项工作的工具，但是我似乎无法发现可以无错误编译的模板参数的任何组合.

From my reading it looks like CMap is the tool for the job, but I can't seem to discover any combination of template arguments that compiles without errors.

我的值是CString和int.我尝试了以下定义:

My values are CString and int. I tried the following definition:

CMap<int, int, CString, CString> encodermap;

可以编译，但是当我尝试添加一个值时:

which compiles, but when I try to add a value:

encodermap["Encoder 1"] = 0;

我收到以下编译器错误:

I get the following compiler errors:

error C2057: expected constant expression
error C2466: cannot allocate an array of constant size 0
error C2501: 'encodermap' : missing storage-class or type specifiers
error C2040: 'encodermap' : 'int []' differs in levels of indirection from 'CMap<KEY,ARG_KEY,VALUE,ARG_VALUE>'

我尝试将CMap更改为此:

CMap<CString, CString, int, int> encodermap;

但是我遇到了同样的四个错误.

but I get the same four errors.

我确定我一定会丢失一些东西，但是我对什么感到茫然.

I'm sure I must be missing something but I'm at a loss as to what.

由于要使用此SDK，因此我需要VS2003

Because of the SDK being used for this work I'm require VS2003

推荐答案

问题

我认为您已经将键类型和谷值类型颠倒了.

I think you've inverted the key type and the valye type.

您的原始声明将int定义为要使用operator[]搜索的关键字.因此encodermap[0] = "Encoder 1";将起作用.

Your original declaration defines int as being the key to be searched for with operator[]. So encodermap[0] = "Encoder 1"; would work.

但是当您的编译器看到encodermap["Encoder 1"] = 0;时，他试图找到一个使用char *(或char *可以转换为的东西)并返回int的operator[].最后一条错误消息告诉您，他无法为您的地图找到这样的运算符.

But when your compiler sees encodermap["Encoder 1"] = 0;, he tries to find an operator[] which takes char* (or something to which char * can be converted to) and returns an int. The last error message tells you that he couldn't find such an operator for your map.

使用MSVC 2015，错误消息更加简洁: C2679 .

With MSVC 2015, the error message is more concise: C2679.

解决方案

您应使用CString定义 CMap 键和int值.要知道的诀窍是，对于CString密钥，ARG_KEY应该为LPCWSTR.因此正确的定义是:

You should define your CMap with a CString key and an int value. The trick to know, is that for a CString KEY, the the ARG_KEY should be LPCWSTR . So the right definition would be:

CMap<CString, LPCWSTR, int, int> encodermap;

这允许使用CString作为地图 operator[] .

This permits to use CString as key in the map's operator[].

现在，如果您在Windows上使用MFC，则可能会使用UNICODE和宽字符(因此是LPCWSTR而不是LPCSTR).调用运算符时，您必须使用CString或宽文字:

Now if you use MFC on windows, you probably use UNICODE and wide chars (therefore the LPCWSTR instead of LPCSTR). When calling the operator you then have either to use a CString or a wide literal:

        encodermap[L"Encoder 1"] = 0;
        encodermap[CString("Encoder 2")] = 1;

这篇关于将MFC CMap用于CString int对的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！