对静态变量 Foo::a 的未定义引用？
我收到此错误，但我不知道这意味着什么：
$ mingw32-g++ Test.cpp -o Test.exe
C:\Documents and Settings\BDL\ccksiYhI.o:Test.cpp:(.text+0x11): undefined reference to 'Foo::a'
collect2: ld returned 1 exit status
这是我的代码。
Test.cpp
#include <vector>
#include "Test.h"
int main() {
Foo::a.clear();
return 0;
}
Test.h
#include <vector>
class Foo {
public:
static std::vector<int> a;
};
这不是我的原始代码，但我已将其归结为这个问题。我是 C++ 新手，如果有人能解释为什么这是错误的以及我如何解决它，我将不胜感激。
I am getting this error and I have no idea what it means:
$ mingw32-g++ Test.cpp -o Test.exe
C:\Documents and Settings\BDL\ccksiYhI.o:Test.cpp:(.text+0x11): undefined reference to 'Foo::a'
collect2: ld returned 1 exit status
This is my code.
Test.cpp
#include <vector>
#include "Test.h"
int main() {
Foo::a.clear();
return 0;
}
Test.h
#include <vector>
class Foo {
public:
static std::vector<int> a;
};
This isn't my original code but I have boiled it down to this problem. I am new to c++ and if anyone can explain why this is wrong and how I can work around it I would appreciate it.
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评论（3）
您仍然需要定义成员变量，即使它是静态的。将您的 Test.cpp 更改为：
You still need to define the member variable, even if it's static. Change your Test.cpp to this:
您还需要在一个翻译单元中定义静态成员，例如在
Test.cpp中：You need to define static members as well in one translation unit, e.g. in
Test.cpp:静态成员必须在类外部定义。里面有一份声明。
网上有很多网站都有示例。搜索“定义 C++ 静态成员”。
祝你好运，欢迎来到 SO。
Static members must be defined outside the class. Inside you have a declaration.
There are many sites online with examples. Search for "define C++ static members."
Good luck with it and welcome to SO.