在构建导出包含ATL :: CString成员的类的DLL时，警告C4251 [英] Warning C4251 when building a DLL that exports a class containing an ATL::CString member

问题描述

我正在将一个基于ATL的静态库转换为DLL，并得到以下警告任何导出类使用ATL CString 类（在atlstr.h中找到）：

I am converting an ATL-based static library to a DLL and am getting the following warning on any exported classes that use the ATL CString class (found in atlstr.h):

警告C4251：'Foo :: str_'：class
'ATL :: CStringT'
使用类'Foo'的客户端使用dll接口

warning C4251: 'Foo::str_' : class 'ATL::CStringT' needs to have dll-interface to be used by clients of class 'Foo'

我正确地声明了 Foo 类通过 __ declspec（dllexport）导出。这是一个警告，我可以安全地忽略或我做错了什么？ DLL项目设置被设置为与ATL动态链接，但这似乎没有任何区别。

I am correctly declaring the Foo class as exported via __declspec(dllexport). Is this a warning I can safely ignore or am I doing something wrong? The DLL project settings are set to dynamically link with ATL, but this doesn't seem to make any difference.

例如：

#ifdef DLLTEST_EXPORTS
#define DLLTEST_API __declspec(dllexport)
#else
#define DLLTEST_API __declspec(dllimport)
#endif

// This class is exported from the DLLTest.dll
class DLLTEST_API Foo
{
public:
 Foo();
 CString str_; // WARNING C4251 HERE
};

此DLL的所有客户端也将使用ATL。

All clients of this DLL will also be using ATL.

推荐答案

这个线程给出了我认为更好的答案，由Doug Harrison（VC ++ MVP）：

This thread gives what I consider a better answer, by Doug Harrison (VC++ MVP):

[此警告是]在
dllexported类Y中使用
a非dllexported类X时发出。这是很糟糕
？嗯，假设Y有一个
内联函数y_f，它调用一个
函数x_f属于X，即
也不是inline。如果y_f是内联的
在一些客户端不
静态链接X，链接将失败，
，因为x_f将无法找到。

[This warning is] emitted when you use a non-dllexported class X in a dllexported class Y. What's so bad about that? Well, suppose Y has an inline function y_f that calls a function x_f belonging to X that is not also inline. If y_f is inlined inside some client that doesn't statically link X, the link will fail, because x_f won't be found.

这篇关于在构建导出包含ATL :: CString成员的类的DLL时，警告C4251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！