C++ 如何从初始化列表中分配数组
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how to assign an array from an initializer list
提问by Dalek
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
我对c++ 的了解有限。我试图编译一个C++库，当我运行以下头文件的 make 文件时
mcmc_dhs.h
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:
它返回以下错误消息：
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.
如果有人可以提供帮助，我将不胜感激。
回答by vsoftco
You cannot assign directly to an array after its declaration. Basically your code is the same as
您不能在声明后直接分配给数组。基本上你的代码是一样的
int main()
{
double arr[2][2];
arr = { {1, 2}, {3, 4.5} }; // error
}
You have to either assign the value at declaration
您必须在声明时分配值
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:
或使用循环（或std::copy）来分配元素。由于您的数组似乎是一个成员变量，您还可以在构造函数初始化列表中对其进行初始化：
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
}
回答by Miles C.
when you said:
当你说：
boundaries =
{{0,512},{0,512},{0.01,5.},{100.,3000.},{0.1,50}};
it was incorrect because c++ does not let you reassign array values. There is an easy work around, but it is somewhat tedious. All you have to do is assign the values one by one. For example:
这是不正确的，因为 C++ 不允许您重新分配数组值。有一个简单的解决方法，但它有点乏味。您所要做的就是一一分配值。例如：
boundaries[0][0] = 0;
boundaries[0][1] = 512;
boundaries[1][0] = 0;
boundaries[1][1] = 512;
and so on. I had this same problem in an Arduino program.
等等。我在 Arduino 程序中遇到了同样的问题。
**I am NOT a c++ connoisseur so this is subject to incorrectness.
**我不是 C++ 鉴赏家，所以这可能有误。
