CODEWITHSUNDEEP
cc++11compiler-errors
Soo
Soo

Reputation: 1017

Using C++11 and C libraries together for complex numbers

I would like to use a C Library and a C++11 library in my application. It seems the usage of "complex" in the C and C++11 library conflicts, and it produces compilation error. A MWE is given here.

Contents of myLib_C.h:

#ifndef MYLIBC_H
#define MYLIBC_H
#include <math.h>
#include <complex.h>
#ifdef  __cplusplus
extern "C" {
#endif
typedef float complex cfloat;
typedef double complex cdouble;
#define myFunc_cfloat(r,i) ((float)(r) + ((float)(i))*I)
#define myFunc_cdouble(r,i) ((double)(r) + ((double)(i))*I)
#ifdef __cplusplus
} // extern "C"
#endif
#endif

The contents of myLib_CPP.h:

#ifndef MYLIBCPP_H
#define MYLIBCPP_H

#include "myLib_C.h" //uses myLib_C somewhere in this file
#include <iostream>
#include <complex>
inline void CppFunction()
{
    std::cout<<"This file need to be compiled using C++11\n";
    std::complex<float> a(10,100);
    std::complex<float> b(1, 1);
    auto c = a+b;
    std::cout<<"c= "<<c<<std::endl;
}

#endif // MYLIBCPP_H

My main.cpp:

#include "myLib_C.h"
#include "myLib_CPP.h"
#include <iostream>
#include <complex>
int main()
{
    std::cout<<"Hello World\n";
    CppFunction();
    return 0;
}

The contents of CMakeLists.txt:

cmake_minimum_required(VERSION 3.10)
project(myTest)
set(CMAKE_CXX_FLAGS "-std=c++11")
add_executable(myTest main.cpp)

When I compile, I get the following error:

error: expected initializer before ‘cfloat’
     typedef float complex cfloat;

A similar problem was discussed in C Complex Numbers in C++?. The solution mentioned there is to replace complex with _Complex. This is not possible in my case as I will not be able to edit the C and C++ libraries.

Upvotes: 2

Views: 527

Answers (1)

n. m. could be an AI
n. m. could be an AI

Reputation: 119857

extern "C" { ... } doesn't magically turn C code inside braces into valid C++ code, so this is out.

Both language standards require their respective complex numbers to have the same layout as an array of two numbers of the corresponding floating-point type (i.e. both C++ std::complex<float> and C float complex behave just like float[2], layout-wise). You can exploit this. For example:

#ifdef  __cplusplus
   using cfloat = std::complex<float>;
#else
   typedef float complex cfloat;
#endif

Now you can declare a cfloat variable in one language and pass it to the other language, and this should work.

Upvotes: 6

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