类型转换std :: complex< double>去__complex128

问题描述

我试图在GCC中使用quadmath库。我有一个复杂的double值，我想将其转换为相应的四元精度复数， __ complex128 。以下是一个最小（非）工作的例子：

  #include< quadmath.h> 
 #include< complex> 
 #include< stdio.h> 
使用namespace std :: complex_literals; 
 
 int main（）{
 std :: complex< double> x = 1 + 2i; 
 std :: printf（x =％5.5g +％5.5g\\\
，x.real（），x.imag（））; 
 __complex128 y = 2 + 2i; 
 y = x; 
返回0; 
 
 $ / code> 

当我尝试使用



  g ++ test.cpp -lquadmath -o test 
  

我得到以下错误：



  test.cpp：10：6：error：can not convert'std :: complex< ; double>'to'__complex128 {aka __complex__ __float128}'in 
y = x; 
  

如果我尝试用明确的类型转换替换赋值行，

  y =（__complex128）x; 
  

我得到一个类似的错误



  test.cpp：10：21：error：从类型'std :: complex< double>'类型转换为'__complex128 {a_ __complex__ __float128}'
y =（__complex128）x ; 
  

如何在这两种类型之间转换？


解决方案

我猜你正在使用GCC，在这种情况下，你可以使用 __ real __ 和 __ imag__ 扩展程序来设置 __ complex128 的单个组件：


  __ complex128 y; 
 __real__ y = x.real（）; 
 __imag__ y = x.imag（）; 
  

这也适用于__complex64的Clang（Clang还不支持__complex128）。 >


I'm trying to use the quadmath library in GCC. I have a complex double value I'd like to typecast into the corresponding quad precision complex number, __complex128. The following is a minimal (non)-working example:

#include <quadmath.h>
#include <complex>
#include <stdio.h>
using namespace std::complex_literals;

int main(){
   std::complex<double> x = 1 + 2i;
   std::printf("x = %5.5g + %5.5g\n", x.real(), x.imag()); 
   __complex128 y = 2+2i;
   y = x;
  return 0;
}

When I try compiling this code with

 g++ test.cpp -lquadmath -o test

I get the following error:

test.cpp:10:6: error: cannot convert 'std::complex<double>' to '__complex128 {aka __complex__ __float128}' in assignment
y = x;

If I try replacing the assignment line with an explicit type cast,

y = (__complex128) x;

I get a similar error

test.cpp:10:21: error: invalid cast from type 'std::complex<double>' to type '__complex128 {aka __complex__ __float128}'
y = (__complex128) x;

How does one convert between these two types?

解决方案

I guess you're using GCC, in which case you can use the __real__ and __imag__ extensions to set the individual components of your __complex128:

__complex128 y;
__real__ y = x.real();
__imag__ y = x.imag();

This works in Clang for __complex64, too (Clang doesn't yet support __complex128).

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