C Complex Numbers in C++?

c++, c99, complex-numbers

Solution

Use the C keyword for complex: _Complex. C++ uses complex as a (template) class. I'm not sure where creal is or I would uncomment that.

#include <complex.h>
#include <cstdio>

int main(int argc, char * argv[]) {
  double _Complex a = 3.0 + 0.0I;  // DECLARATION WORKS NOW - NOTE ASSIGNMENT MUST HAVE IMAG PART
  //printf("%lf\n", creal(a));
  return 0;
}

This works in gcc (I compiled with g++). I got a warning about deprecated .h headers.

Here is a link to an email trail showing nonstandard compatibility with C++ and C with complex numbers. C++11 requires layout compatibility of C++ complexes with C _Complexes.

I'm currently investigating creal, etc. in C++. I'm not finding anything in the standard. Since there seems to be some effort to provide some source compatibility between C++ and C then creal, cpow, etc. might make a nice addition to TR2 the library proposals.

Problem

The following code compiles and runs just fine in C (at least according to 'gcc -std=gnu99'), but it fails to compile under C++, giving "line 5: error: cannot convert 'double' to 'double complex' in initialization". Does anybody know why? ``` #include "/usr/include/complex.h" #include <stdio.h> int main(int argc, char * argv[]) { double complex a = 3; // ERROR ON THIS LINE printf("%lf\n", creal(a)); return 0; } ``` I realize there is another way of doing complex numbers in C++, but I have to use C complex numbers in C++, because that is how the legacy code I was given does things. Thanks if you can help!

Original source