G++ 4.5 中 std::complex 的 C++11 复制赋值 - 与 'operator+' 不匹配

Question

下面的代码无法使用 -std=c++0x 开关在 g++ 4.5.0 版中编译。我收到以下错误消息:

error: no match for 'operator+' in 'std::pow [with _Tp = float, _Up = int, typename __gnu_cxx::__promote_2<_Tp, _Up>::__type = double](((const std::complex<float>&)((const std::complex<float>*)(& x))), ((const int&)((const int*)(&2)))) + y'

我相信这与提到的可分配要求有关here .我应该为 complex 定义自己的复制赋值运算符吗？如果是，怎么办？

#include <complex>
using namespace std;

int main(int argc, char *argv[]) {
  complex<float> x,y;
  x = pow(x,2);      // ok
  x = x        + y;  // ok
  x = pow(x,2) + y;  // error
  return 0;
}

Answer 1

[cmplx.over]/p3 为 pow 指定额外的重载什么时候complex涉及:

Function template pow shall have additional overloads sufficient to ensure, for a call with at least one argument of type complex<T>:

1. If either argument has type complex<long double> or type long double, then both arguments are effectively cast to complex<long
double>.

2. Otherwise, if either argument has type complex<double>, double, or an integer type, then both arguments are effectively cast to complex<double>.

3. Otherwise, if either argument has type complex<float> or float, then both arguments are effectively cast to complex<float>.

2 被提升为 double ，并且 pow(complex<float>, double)返回 complex<double> .