how to assign an array from an initializer list

问题

I have a limited knowledge about c++. I tried to compile a c++ library and when I run the make file for the following header file

mcmc_dhs.h

#include <algorithm>
#include <map>

// intrinsic shape and (reduced) shear just add?
//#define WLNOISE

// use shear instead of reduced shear for model
//#define NOREDSHEAR

/// parameters for the M200-concentration relation
const number mcreal[2] = {9.59,-0.102}; // Dolag et al. (2004)
//const number mcreal[2] = {5.26,-0.100}; // Neto et al. (2007) [Millenium Run]

/// critical density at z=0 (h100=1) in [Msun/Mpc^3]
const number rhocrit = exp(log(rhoCrit)+3.*log(Mpc)-log(Msun)); 

/// two extra halo parameters: r200 (and concentration: 2)
#define PARAMS 1

/// define region (square; twice value here) about halo that considers sources for model
#define REGION 10.0*arcmin

class mcmc_dhs : public mcmc
{
 public:

  mcmc_dhs() : 
  data(), cosmohandler(0.3,0.7,0.21,0.8,0.04),
    lenseff(), intrvar()
    {
      boundaries = 
    {{0,512},{0,512},{0.01,5.},{100.,3000.},{0.1,50}};
    }
  ~mcmc_dhs() {}

  /// size of grid for looking up sources
  static const int Ngrid = 200;

It returns the following error message:

mcmc_dhs.h:55:67: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11 [enabled by default]
      boundaries = {{0,512},{0,512},{0.01,5.},{100.,3000.},{0.1,50}};
                                                                   ^
mcmc_dhs.h:55:17: error: assigning to an array from an initializer list
      boundaries = {{0,512},{0,512},{0.01,5.},{100.,3000.},{0.1,50}};
                 ^
In file included from ../modules/matrix.h:15:0,
                 from ../modules/probdensity.h:4,
                 from ../modules/mcmc.h:4,
                 from mcmc_dhs.h:4,

I would appreciate if someone can help.

回答1:

You cannot assign directly to an array after its declaration. Basically your code is the same as

int main()
{
    double arr[2][2];
    arr = { {1, 2}, {3, 4.5} }; // error
}

You have to either assign the value at declaration

double arr[2][2] = { {1, 2}, {3, 4.5} };

or use a loop (or std::copy) to assign elements. Since your array seems to be a member variable, you can also initialize it in the constructor initialization list:

 mcmc_dhs() : data(), cosmohandler(0.3,0.7,0.21,0.8,0.04), 
              lenseff(), intrvar(), 
              boundaries{{0,512},{0,512},{0.01,5.},{100.,3000.},{0.1,50}}
 { 
    // rest of ctor implementation
 }

来源：https://stackoverflow.com/questions/30178879/how-to-assign-an-array-from-an-initializer-list

标签

c++

arrays

initializer-list