Alexander McFarlane Alexander McFarlane - 5 months ago 16
C++ Question

Why are `ccos`, `csqrt`, `cpow` not recognised?

Why am I getting these errors? (I have a


error: use of undeclared identifier 'ccos'
error: use of undeclared identifier 'csqrt'; did you mean 'sqrt'?
error: use of undeclared identifier 'cpow'; did you mean 'pow'?

and so forth. I have declared my function as:

#include <complex>

double ghmc1AccNormalised( double ph, double r, double t, double th){

complex<double> numerator;
complex<double> denominator;
double E = exp(1);

numerator=-(cpow(E,t*((-2*r + r*ccos(th) + r* // ... etc
// what follows is 24MB of a horrible polynomial from Mathematica
denominator = cpow(2,0.3333333333333333) //... etc

return creal(numerator/denominator);

I am trying to ensure that I am handling the imaginary variables correctly.
I have spent a long time looking at various posts but I have the following issues:

  • The values are coming out as
    when they shouldn't

  • I suspected that this was due to complex numbers not being handled properly

  • This highly rated post notes that
    etc. should be used for complex arguments

  • I have tried various namespaces in addition to the above:

    • using complex;

    • using std::complex;

    • I tried also prepending
      to each function


You are using functions from the C header complex.h, which you are not including. But the C++ header complex provides overloads for cos, sin, pow, etc*. You should use these instead of their C counterparts.

#include <complex>

int main()
    std::complex<double> c{1, 2};
    auto c2 = pow(c, 2);
    auto cc = sqrt(c2);

* Note that these are in the std namespace, but so is std::complex, so argument dependent lookup (ADL) allows you to invoke them without the namespace.