Use of <complex> and function matching

[mainecat]

Hi all, can you help me figure out why this code doesn't work. The function call to exp() should call the function defined in the complex library. But I have to either give it a complex arg or explicitly convert it to a complex. I would think it would automatically convert to the correct type by matching the arg type.

  /*use of complex numbers. Euler's formula to compute exp(i*PI)=-1 */
#include <cmath>
#include <complex>
#include <iostream>
#include <iomanip>

const double PI {std::acos(-1)};

int main() {
           std::cout << std::fixed << std::setprecision(2);
           std::complex<double> z0,z1;
           z0 = 1i * PI;
           std::cout << "i * pi = " << z0 << '\n';
           z1 = std::exp(z0);                                   //works
//         z1 = std::exp(1i * PI);                              //ERROR!
           z1 = std::exp((std::complex<double>) 1i * PI);       //works
           std::cout << "exp(i * pi) = " << z1 << '\n';
           return 0;
}

I'm using g++ (GCC) 7.3.0 with no options.

thank you,
Scott

[lastchance]

Try your code in C++ shell (gear-wheel icon to the top right of the code sample).

Your marked line is not the only problem with your code.

I think you may have been relying on a few non-standard compiler extensions.

[mainecat]

I tried the C++ Shell and it does not compile. But I'm using GNU GCC. My code compiles under GNU GCC (under Ubuntu, MinGW/MSYS, and Cygwin).

My code does rely on complex_literals (in C++14), but these are recognized by default by the GCC version (except the older version uder Ubuntu, which requires -std=c++14 to compile). Otherwise I did not specify any compiler options.

But even if I explicitly give the command-line options, it still give the same error: it cannot find the function based on the arg list. It recognizes the literals, and it seems to be correctly converting the mixed data-type arg to a complex data type, but it seems to be unable to find the exp() function from the complex library:

g++ -std=c++14 -fext-numeric-literals -Wall test_complex.cpp
test_complex.cpp: In function ‘int main()’:
test_complex.cpp:16:26: error: no matching function for call to ‘exp(__complex__ double)’
     z1 = std::exp(1i * PI);   
                          ^

[JLBorges]

> I'm using g++ (GCC) 7.3.0 with no options.

Compile with -std=c++14 -Wall -Wextra -pedantic-errors

This is required for complex literals to be available: using namespace std::literals ;
More information: https://en.cppreference.com/w/cpp/numeric/complex/operator%22%22i

With these, the code works as expected: http://coliru.stacked-crooked.com/a/b18a1d7f760b399c

[mainecat]

I thought I did that already, but I guess I missed it. Thank you!

Addendum: I think I found the source of my error. I found that if I include the namespace complex_literals in my code and give the command line option -fext-numeric-literals, then the compiler issues an error.

           using namespace std::complex_literals;

 g++ -std=c++14 -fext-numeric-literals   test_complex.cpp
test_complex.cpp: In function ‘int main()’:
test_complex.cpp:16:26: error: no matching function for call to ‘exp(__complex__ double)’
     z1 = std::exp(1i * PI);    //ERROR!