"Cannot declare member function ...to have static linkage"错误

基本的语法错误，郁闷了我半天，相关的资料可以参考：http://cplusplus.syntaxerrors.info/index.php?title=Cannot_declare_member_function_%E2%80%98static_int_Foo::bar()%E2%80%99_to_have_static_linkage

英文解释：

if you declare a method to be static in your .cc file.

The reason is that static means something different inside .cc files than in class declarations It is really stupid, but the keywordstatic has three
different meanings. In the .cc file, the static keyword means that the function isn't visible to any code outside of that particular file.

This means that you shouldn't use static in a .cc file to define one-per-class methods and variables. Fortunately, you don't need it. In C++, you are not allowed to have static variables or static methods with the same name(s) as instance variables
or instance methods. Therefore if you declare a variable or method as static in the class declaration, you don't need the statickeyword in the definition. The compiler still knows that the variable/method is part of the class and not the instance.

错误的：

Foo.h:

class Foo

{

public:

static int bar();

};

Foo.cc:

static int Foo::bar()

{

// stuff

}

正确的：

Foo.h:

class Foo

{

public:

static int bar();

};

Foo.cc:

int Foo::bar()

{

// stuff

}

这个也是正确的：

Foo.h:

class Foo

{

public:

static int bar()

{

// stuff

};

};