c++ - 应用回调来调用 gsl_integration

Question

我是c++的新手，我正在尝试修改代码并在名为Cosmology的类中使用c的gsl_integration库。为了分配成员函数以形成 gsl 的指针，我使用了通过在互联网上查找找到的回调过程

更新:Cosmology.h

#include <cmath>
#include <gsl/gsl_integration.h>


struct CCallbackHolder
{
  Cosmology* cls;
  void* data;
};

class Cosmology {
private:
    static const double c = 299792458.0, Mpc2Km = 3.08567758e+19, Yrs2Sec = 3.15569e7;
    double H0 = 67.77, OmegaM = (0.022161+0.11889)/(H0*H0), OmegaL = 0.6914, OmegaG = 8.24e-5, OmegaK = 0.0009;
    double Ez(double z);
    double Hz(double z, void* params);
    static double CCallback(double z,void* param)
    {
      CCallbackHolder* h = static_cast<CCallbackHolder*>(param);
      return h->cls->Hz(h->data);
    }
public:
    double distH, timeH;
    Cosmology();
    Cosmology(double);
    Cosmology(double , double );
    Cosmology(double , double , double );
    Cosmology(double , double , double , double );
    Cosmology(double , double , double , double , double );
    double distC(double);
  } cosmo;

宇宙学.cpp

#include <cmath>
#include <gsl/gsl_integration.h>
#include "Cosmology.h"
#include<iostream>
using namespace std;
double Cosmology::Hz(double z, void* params)  {
    double result = 1.0/pow(OmegaL + pow(1.0+z,3.0)*OmegaM + pow(1.0+z,4.0)*OmegaG + pow(1.0+z,2.0)*OmegaK, 0.5);
    return result;
    }

double Cosmology::distC(double z) { 
    double lower_limit = 0.0, abs_error = 1.0e-8, rel_error = 1.0e-8, alpha = 0.0, result, error;
    gsl_integration_workspace *work_ptr = gsl_integration_workspace_alloc(1000);
    gsl_function Hz_function;
    void* params_ptr = &alpha;
    Hz_function.function = &Cosmology::CCallback;
    Hz_function.params = params_ptr;
    gsl_integration_qags(&Hz_function, lower_limit, z, abs_error, rel_error, 1000, work_ptr, &result, &error);
    return distH*result;
    }
using namespace std;    
int main () {
  Cosmology cosmo;
  cout << "Comoving Distance: " << cosmo.distC (0.3);
  return 0;
}

当我尝试编译代码时出现以下错误:

Cosmology.h:10: error: ISO C++ forbids declaration of ‘Cosmology’ with no type
Cosmology.h:10: error: expected ‘;’ before ‘*’ token
Cosmology.h:16: error: ISO C++ forbids declaration of ‘constexpr’ with no type
Cosmology.h:16: error: expected ‘;’ before ‘double’
Cosmology.h:17: error: ISO C++ forbids declaration of ‘constexpr’ with no type
Cosmology.h:17: error: expected ‘;’ before ‘double’
In file included from Universe.cpp:3:
Cosmology.h: In static member function ‘static double Cosmology::CCallback(double, void*)’:

通过使用以下行进行编译:g++ -Wall -pedantic Cosmology.cpp -o Cosmology std=c++0x。我该如何修复代码？

Answer 1

程序的主要问题是在声明类成员的非静态变量时对其进行初始化，这不是合法的 C++ 操作。具体来说，问题在于以下几行:

static constexpr double c = 299792458.0, Mpc2Km = 3.08567758e+19, Yrs2Sec = 3.15569e7;

double H0 = 67.77, OmegaM = (0.022161+0.11889)/(H0*H0), OmegaL = 0.6914, OmegaG = 8.24e-5, OmegaK = 0.0009;

c、Mpc2Km、Yrs2Sec、H0、OmegaM、OmegaL、OmegaG、OmegaK 是非静态、非常量和 double 。如果你想初始化它们(即给它们赋值)，你必须在 Cosmology 类构造函数中完成，或者将它们移到类声明之外，从而使它们成为全局变量，但请注意，你应该避免全局变量，除非你知道什么你这样做，没有其他办法。

如果您想像您尝试的那样在头文件中初始化它们，它们必须是整型 - 不适用于 double 型。

简而言之:第一行不起作用，因为类型是 double (只有整型 static const 类型可以在类声明中初始化)；第二个不起作用，因为类型是非常量、非静态和 double 的。

一旦这些行被修复，其余的错误可能就会消失。