C++/Fortran 混合编程 : undefined reference to `_gfortran_reshape_r8'

Question

我正在编译 C++ 代码和 Fortran 子例程。 C++ cpp 代码如下:

#include "Calculate.h"
extern "C" double SolveEq_(double *Gvalue, double *GvalueU, double *GvalueV, double *Gnodex, double *Gnodey, double *GtimeInc, double *Glfs);

template <class T1, class T2>
void Calculate(vector<Element<T1, T2> > &elm, GParameter &GeqPm, GmeshInfo &Gmesh)
{
    // Solving Equation using Fortran code
    SolveEq_(&Gmesh.Gvalue[0], &Gmesh.GvalueU[0], &Gmesh.GvalueV[0], &Gmesh.Gnodex[0], &Gmesh.Gnodey[0], &GeqPm.GtimeInc, &GeqPm.Glfs);
    return;
}

Fortran 代码如下:

!==========================================================================
Module Inputpar
Implicit None
Integer,parameter :: Numx = 200, Numy = 200
End Module
!======================================== PROGRAM =============================================
Subroutine SolveEq(Gvalue, GvalueU, GvalueV, Gnodex, Gnodey, Deltat, Lfs);
Use Inputpar
Implicit None

Real*8 Deltat, Lfs, Dt, Su
Real*8 Gvalue(1, (Numx+1)*(Numy+1)), GvalueU(1, (Numx+1)*(Numy+1)), GvalueV(1, (Numx+1)*(Numy+1))
Real*8 Gnodex(0:Numx), Gnodey(0:Numy)

Real*8 DX, DY
Real*8 X(-3:Numx+3), Y(-3:Numy+3)
Real*8 VelX(-3:Numx+3,-3:Numy+3), VelY(-3:Numx+3,-3:Numy+3)
Real*8 G(-3:Numx+3,-3:Numy+3)

Common /CommonData/ X, Y, DX, DY, VelX, VelY, G, Dt, Su

!============================= Data Transfer ============================
Dt                  = Deltat
Su                  = Lfs
X          (0:Numx) = Gnodex(0:Numx)
Y          (0:Numy) = Gnodey(0:Numy)
VelX(0:Numx,0:Numy) = transpose(reshape(GvalueU,(/Numy+1,Numx+1/)))
VelY(0:Numx,0:Numy) = transpose(reshape(GvalueV,(/Numy+1,Numx+1/)))
G   (0:Numx,0:Numy) = transpose(reshape(Gvalue ,(/Numy+1,Numx+1/)))

!==========Some other lines neglected here=================

End
!======================================== END PROGRAM =========================================

首先使用命令编译 Fortran 代码:

      gfortran SolveEq.f90 -c -o SolveEq.o

然后使用 makefile 将 C++/Fortran 代码编译在一起:

# Compiler
CC = g++

# Debug option
DEBUG = false

# Source directory of codes
SRC1 = /home
SRC2 = $(SRC1)/Resources
SRC3 = $(SRC1)/Resources/Classes

OPT=-fopenmp -O2

ifdef $(DEBUG)
  PROG=test.out
else
  PROG=i.out
endif

# Linker
#LNK=-I$(MPI)/include -L$(MPI)/lib -lmpich -lopa -lmpl -lpthread

OBJS = libtseutil.a Calculate.o SolveEq.o

OBJS_F=$(OBJS)
SUF_OPTS1=$(OBJS_F)
SUF_OPTS2=-I$(SRC2)/
SUF_OPTS3=-I$(SRC3)/
SUF_OPTS4=

# Details of compiling
$(PROG): $(OBJS_F)
    $(CC) $(OPT) -o $@ $(SUF_OPTS1)
%.o: $(SRC1)/%.cpp
    $(CC) $(OPT) -c $< $(SUF_OPTS2)
%.o: $(SRC2)/%.cpp
    $(CC) $(OPT) -c $< $(SUF_OPTS3)
%.o: $(SRC3)/%.cpp
    $(CC) $(OPT) -c $< $(SUF_OPTS4)

# Clean
.PHONY: clean
clean:
    @rm -rf *.o *.oo *.log

但是，错误显示:

g++ -fopenmp -O2 -o libtseutil.a Calculate.o SolveEq.o
Calculate.o: In function `void Calculate<CE_Tri, SolElm2d>(std::vector<Element<CE_Tri, SolElm2d>, std::allocator<Element<CE_Tri, SolElm2d> > >&, GParameter&, GmeshInfo&)':
Calculate.cpp:(.text._Z10CalculateGI6CE_Tri8SolElm2dEvRSt6vectorI7ElementIT_T0_ESaIS6_EER10GParameterR9GmeshInfo[_Z10CalculateGI6CE_Tri8SolElm2dEvRSt6vectorI7ElementIT_T0_ESaIS6_EER10GParameterR9GmeshInfo]+0x3c): undefined reference to `SolveEq_'
SolveEq.o: In function `solveeq_':
SolveEq.f90:(.text+0x2b8e): undefined reference to `_gfortran_reshape_r8'
SolveEq.f90:(.text+0x2d2a): undefined reference to `_gfortran_reshape_r8'
SolveEq.f90:(.text+0x2ec6): undefined reference to `_gfortran_reshape_r8'
SolveEq.f90:(.text+0x31fa): undefined reference to `_gfortran_reshape_r8'
collect2: error: ld returned 1 exit status

这是怎么发生的？

我用一个简单的案例来测试混合编译。 C++ 代码是:

#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;

extern "C" double fortran_sum_(double *sum, double *su2m, double *vec, double* vec2, int *size);

int main(int argc, char ** argv)
{
    int size;
    double sum, sum2;
    double aa,bb,cc,dd;
    vector<double> vec;
    vector<double> vec2;

    size=2;
    aa=1.0;
    bb=2.0;
    sum=0.0;
    sum2=0.0;

    vec.push_back(aa);
    vec.push_back(bb);
    vec2.push_back(aa*2.0);
    vec2.push_back(bb*2.0);

    fortran_sum_(&sum, &sum2, &vec[0], &vec2[0], &size);

    cout << "Calling a Fortran function" << endl;
    cout << "============================" << endl;
    cout << "size = " << size << endl;
    cout << "sum = " << sum << endl;
    cout << "sum2 = " << sum2 << endl << endl;
}

Fortran 代码是:

Subroutine fortran_sum(gsum, gsum2, gvec, gvec2, gsize2)
  integer gsize,gsize2
  real*8 gvec(0:gsize2-1), gvec2(0:1)
  real*8 gsum, gsum2
  gsum = gvec(0)+gvec(1);
  gsum2 = gvec2(0)+gvec2(1);
  gsize = gsize*2;
end 

然后使用命令编译:

gfortran fortran_sum.f90 -c -o fortran_sum.o
g++ fortran_sum.o call_fortran.cpp -o a.out
./a.out

效果很好:

Calling a Fortran function
============================
size = 2
sum = 3
sum2 = 6

Answer 1

_gfortran_reshape_r8 函数是 gfortran 编译的代码使用的库的一部分。当你用一种语言编译时，这些库会自动链接，因为无论你用来链接的程序都知道它们。当您链接混合代码时，您需要找到并在命令行上显式放置与您选择的链接器不对应的语言的库。通常您使用 C++ 语法链接，就像您在此处所做的那样，并显式添加 fortran 编译器的库。