c++ display complex number with i in imaginary part

Question

I am doing something like:

int real_part, imaginary_part;
cout<<"Please enter realpart and imaginary part"<<endl;
cin>>real_part;
cin>>imaginary_part;
complex<double> mycomplex (real_part, imaginary_part);
cout<<mycomplex<<endl; // I want to display like -2+5i but I get (-2, 5)

I am very new to c++

How can I display with i like -2+5i ? Or I have to add i char with imagginary part ?

Answer 1

You can use std::real() and std::imag() to format as you like, see complex here .

Of course, you will have to check for sign yourself.

Something like this:

std::cout
   << std::real(mycomplex)
   << (std::imag(mycomplex) >= 0.0 ? "+" : "")
   << std::imag(mycomplex)
   << " i"
   << std::endl;

Answer 2

您可以简单地写：

cout<< mycomplex.real << std::showpos << mycomplex.imag << "i" << endl;

Answer 3

For the sake of completeness with the other answer. You can use std::showpos to more easily format the output into something signed

cout << real(mycomplex) << std::showpos << imag(mycomplex) << "i";

Answer 4

If you're feeling really sneaky, or are using libraries that you dont want to or cant modify everywhere (ie I use this to print Eigen matrices in an octave / matlab compatible format), you can specialize the put-to operator for your type before including <complex> . I suspect that this is against the standard, because it mucks around in std:: , but it works in g++(7.3.1) and clang++(5.0):

/*
 * this stuff can go in a header to make std::complex<> available
 */
typedef double real_t;

#include <iostream>

#define SPECIALIZED_COMPLEX_PUTTO
#ifdef SPECIALIZED_COMPLEX_PUTTO
#ifdef _LIBCPP_BEGIN_NAMESPACE_STD // for clang++ libs
_LIBCPP_BEGIN_NAMESPACE_STD
#else
namespace std {
#endif
template <typename T> class complex;

template <class T, class CharT, class Traits>
std::basic_ostream<CharT, Traits>&
operator<<(std::basic_ostream<CharT, Traits>& os,
  const std::complex<T>& x);

// specialization for real_t, instantiate later
template<>
basic_ostream<char>&
operator<<(basic_ostream<char> & o, const complex<real_t> & x);
#ifdef _LIBCPP_END_NAMESPACE_STD // for clang++
_LIBCPP_END_NAMESPACE_STD
#else
}
#endif


#include <complex>

/*
 * below here can go in a .cpp file
 */

#ifdef SPECIALIZED_COMPLEX_PUTTO
#ifdef _LIBCPP_BEGIN_NAMESPACE_STD // for clang++ libs
_LIBCPP_BEGIN_NAMESPACE_STD
#else
namespace std {
#endif
template<>
basic_ostream<char>&
operator<<(basic_ostream<char> & o, const complex<real_t> & x)
{
  basic_ostringstream<char> s;
  s.flags(o.flags());
  s.imbue(o.getloc());
  s.precision(o.precision());
  s << x.real() << std::showpos << x.imag() << 'i';
  return o << s.str();
}
#ifdef _LIBCPP_END_NAMESPACE_STD // for clang++
_LIBCPP_END_NAMESPACE_STD
#else
}
#endif


int main(int argc, char * argv[])
{
  std::complex<real_t> x(1.1,-2.2);
  std::cout << x << "\n";
}

outputs

1.1-2.2i

alternately, an example main() for the Eigen case:

#include <Eigen/Dense>
int main(int argc, char * argv[])
{
  Eigen::Matrix<std::complex<real_t>, 3,3> x;
  Eigen::IOFormat OctaveFmt(Eigen::StreamPrecision, 0, ", ", ";\n", "", "", "[", "]");
  //srand((unsigned int) time(0));
  x.setRandom();
  std::cout << x.format(OctaveFmt) << "\n";
}

outputs a matrix in a format suitable for copy/paste into octave/matlab:

[  0.680375-0.211234i,  -0.329554+0.536459i, -0.270431+0.0268018i;
    0.566198+0.59688i,   -0.444451+0.10794i,    0.904459+0.83239i;
   0.823295-0.604897i, -0.0452059+0.257742i,   0.271423+0.434594i]

Edit: added macros for apple clang libs.