问题描述
我试图来存储一个boost ::函数作为静态变量，其中参考？是从一个函数取得。
I'm trying to store a boost::function as a static variable where the "reference?" is fetched from a function.
变量是这样的：
static boost::function<void( const wchar_t*, const bool)> s_logMessage;
当我尝试编译我的错误：
When I try to compile I get the error:
错误LNK2001：解析外部符号？市民：静态类boost ::功能Gorbatras_Converter :: ConverterApp :: s_logMessage（s_logMessage @ ConverterApp @ Gorbatras_Converter @@ 2V $ @功能$$ A6AXPB_W_N @ Z @提振@@一）
我注意到，如果我不使用变量，我可以编译它，而不该错误（猜这是一个编译器的优化，因为它没有使用），但只要我尝试使用s_logMessage变量我得到的链接错误
I've noticed that if I don't use the variable I can compile it without that error (guess it's a compiler optimization since it's not used) but as soon as I try to use the s_logMessage variable I get the linker error.
我的设置s_logMessage的方式是这样的：
My way of setting s_logMessage looks like this:
const int ConverterApp::RunConverter( boost::function<void( const wchar_t* a_message, const bool a_newLine)> a_logMessage )
{
ConverterApp::s_logMessage = a_logMessage;
...
}
我试着将它设置为一个非静态成员变量，然后它似乎工作。但我需要它作为静态的，否则我可能只是一起藏汉把它作为，因为它的将是一个很大的功能，我不希望有一个参数。
I've tried setting it as a non-static member variable and then it appears to work. But I need it as static, otherwise I might just aswell send it along as a parameter which I don't want as it's going to be a lot of functions.
如果你想知道为什么我发送日志功能为参数，这是因为它来自一个单独的程序。
If you wonder why I'm sending a log function as parameter, that is because it comes from a separate program.
所以我需要帮助的是我怎么救了boost :: function函数在一个静态变量？
So what I need help is how do I save the boost::function function in a static variable?
推荐答案
您错过一个的定义的为静态数据成员（你只有一个的声明的那成员类定义）。将下面的命名空间范围：
You're missing a definition for the static data member (you only have a declaration of that member in your class definition). Put the following at namespace scope:
boost::function<void( const wchar_t*, const bool)> ConverterApp::s_logMessage;
如果你从来不使用数据成员（从技术上讲，如果不是的 ODR使用的的，看到C ++ 11标准第3.2），则不需要定义 - 因此行为你正在观察。
If you never use the data member (technically, if it is not odr-used, see paragraph 3.2 of the C++11 Standard), then the definition is not needed - hence the behavior you are observing.
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