c++ - 如何在另一个类中设置静态变量？

Question

我试图在 Coeffs.cpp 中设置一个静态变量:

#include "Coeffs.h"
class Coeffs
{
    public:
    double Coeffs::alpha5b = 0.0;
};

头文件

#ifndef COEFFS_H
#define GOEFFS_H
class Coeffs
{
    public:
    static double alpha5b;
};
#endif

使用以下代码:

#include <iostream>
#include <fstream>
#include <string>
#include "json/json.h"
#include "Coeffs.h"

using namespace std;

int main()
{
    cout << "start" << endl;

    string json;
    ifstream inputStream;
    inputStream.open("coeffTest.json");
    inputStream >> json;

    Json::Value root;
    Json::Reader reader;
    bool parseSuccess = reader.parse(json, root);
    if(!parseSuccess)
    {
        cout << "failed" << endl;
    }
    else
    {
        Coeffs::alpha5b = 1.1;
        //Coeffs::alpha5b = root.get("alpha5b", "NULL").asDouble();
        //double item1[] = root.get("delta21b", "NULL").asDouble();
        //cout << "alpha5b is: " << Coeffs::alpha5b << endl;
    }
    cout << "done" << endl;
}

但是每次编译我都会得到这个:

pottsie@pottsie:~/Documents/CoeffsJSON$ g++ -o JsonToCoeffs JsonToCoeffs.cpp -ljson_linux-gcc-4.6_libmt
/tmp/ccFxrr0k.o: In function `main':
JsonToCoeffs.cpp:(.text+0x10b): undefined reference to `Coeffs::alpha5b'
collect2: ld returned 1 exit status

我查看了其他一些类似的问题，但找不到任何有效的方法。我试过添加一个构造函数并创建一个对象，但我仍然遇到同样的错误。有人知道该怎么办吗？

Answer 1

类声明应该放在头文件中(Coeffs.h)

#ifndef COEFFS_H
#define COEFFS_H
class Coeffs
{
    public:
    static double alpha5b;
};
#endif

但在源文件(.cpp、.cxx)中初始化静态成员:

#include "Coeffs.h"

double Coeffs::alpha5b = 0.0;