gfortran main的多个定义 [英] gfortran multiple definition of main

问题描述

我在编写一段研究代码时遇到了麻烦.它由一个用C ++编写的组件和另一个用FORTRAN编写的组件组成.我认为问题与我的gcc版本有关.

I'm having trouble with compiling a piece of code I have been given for my research. It consists of one component written in C++ and the other in FORTRAN. I think the problem is to do with my gcc version.

例如，第一个文件是C ++文件(foo.ccp)

The first file for example is a C++ file (foo.ccp)

#include <iostream>
using namespace std;

extern "C" {
  extern int MAIN__();
}

int main(){
    cout << "main in C++\n";
  return MAIN__();
}

第二个是bar.f90:

The second is bar.f90:

program test
    implicit none
    print*, 'MAIN in FORTRAN'
end program test

我正在尝试像这样编译它:

I'm trying to compile it like so:

g++ -c foo.cpp
gfortran foo.o -lstdc++ bar.f90

它可以在GCC-4.4.7上正常编译，但在GCC-4.8.x上却可以读取以下错误:

It compiles fine with GCC-4.4.7 but fails with GCC-4.8.x with the error reading:

/tmp/cc5xIAFq.o: In function `main':
bar.f90:(.text+0x6d): multiple definition of `main'
foo.o:foo.cpp:(.text+0x0): first defined here
foo.o: In function `main':
foo.cpp:(.text+0x14): undefined reference to `MAIN__'
collect2: error: ld returned 1 exit status

我已阅读此处，其中发生了变化从版本4.5.x开始，gfortran如何处理'main'和'MAIN__'函数的命名，但是我不确定如何解决我的问题.

I've read here that there's a change in how gfortran handles naming of the 'main' and 'MAIN__' functions since version 4.5.x but I'm not sure how to fix my problem.

关于我所缺少的东西有什么想法吗?感谢您的帮助！

Any ideas as to what I'm missing? Thanks for your help!

推荐答案

您有两个main符号:

int main(){
    cout << "main in C++\n";
  return MAIN__();
}

和

program test
    implicit none
    print*, 'MAIN in FORTRAN'
end program test

主program被赋予符号main.您不能将这两个程序链接在一起，因为两个main符号冲突.还存在一个问题，因为为Fortran program指定了main符号，而不是给了MAIN__该符号未定义.您的目标是从C ++调用Fortran，您应该这样做:

The main program is given the symbol main. You cannot link these two programs together because the two main symbols conflict. You also have the issue that since the Fortran program is given the main symbol and not MAIN__ that symbol is undefined. Your goal is to call Fortran from C++, you should do this:

#include <iostream>

extern "C" {
  int FortMain();
}

int main()
{
    std::cout << "main in C++\n";
    return FortMain();
}

和

function FortMain() bind(C,name="FortMain")
   use iso_c_binding
   implicit none
   integer(c_int) :: FortMain
   print *, "FortMain"
   FortMain = 0
end function FortMain

这些将编译并链接在一起，并执行您的代码尝试执行的操作.它们利用Fortran的iso_c_binding功能来确保Fortran函数在适当的情况下可以与C完全互操作，并且不会强调任何有趣的事情. Fortran函数还返回一个值，因此与您在示例中提供的C原型匹配.

These will compile and link together and do what your code is attempting to do. These make use of Fortran's iso_c_binding features to ensure the Fortran function is fully interoperable with C with proper case and no underscoring funny business. The Fortran function also returns a value so matches the C prototype your have provided in your example.

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