将动态二维数组从C ++传递到Fortran并返回 [英] Passing a dynamic 2D array from C++ to Fortran and back
问题描述
C ++端
externC{void array2d_（double **，int *，int *）; }
使用namespace std;
int main（）
{
double ** array;
int nx = 3;
int ny = 2;
int i，j;
cout<< 将动态数组从C传递给Fortran \\\
;
array =（double **）malloc（nx * sizeof（double *））;
if（array == NULL）
{
fprintf（stderr，out of memory \\\
）;
出口;
}
for（i = 0; i
array [i] =（double *）malloc（ny * sizeof（double））;
if（array [i] == NULL）
{
fprintf（stderr，out of memory \\\
）;
出口; （i = 0; i
for（j = 0; j
}
b $ b {
array [i] [j] = i + j + i *（2 + j）+4; //随机初始化
cout<< array [<<我<< ] [<< j<< ] =<<数组[i] [j]<< ;
}
cout<< ENDL;
}
array2d_（array，& nx，& ny）; （i = 0; i< nx; i ++）
free（array [i]）;
free（array）;
返回0;
}
Fortran方面
< （c，name =array2d_）
使用iso_c_binding
隐式无
整型（C_INT）$ p $ 子程序array2d（arr，nx_C，ny_C） ，intent（IN）:: nx_C，ny_C！数组大小从C
real（C_DOUBLE），intent（INOUT）:: arr（ny_C，nx_C）
integer :: k，l
print *，这是在Fortran例程中...
do k = 1，ny_C
do l = 1，nx_C
print *，arr（，k，， ，l，）=，arr（k，l）
end do
end do
end subroutine array2d
C ++中的输出是
$ p $ array [0] [0] = 4 array [0] [1] = 5
array [1] [0] = 7 array [1] [1] = 9
array [2] [0] = 10 array [2] [1 ] = 13
在Fortran中，输出是
（1，3）= 9.8813129168249309（$） E-324
ar r（2,1）= 5.4809152658772852E-317
arr（2,2）= 1.5475240269406953E-314
arr（2,3）= 0.0000000000000000
所以不知何故值不能正确传递。
主要原因是你的C数组是一个锯齿形数组，它是一个指向数组的指针数组，当你在Fortran中声明它的参数是一个连续的二维数组时。
只需 malloc 一个大的元素，最好在C中使用相同的数组。 nx * ny 缓冲区，并将指针设置为行而不是分配它们。您可以在 https://stackoverflow.com/a/5901671/721644 中查看示例。
Passing a fixed 2D array between C++ and Fortran works fine, however not so with the program I have written to pass a 2D dynamic array from C++ to Fortran.
C++ side
extern "C" {void array2d_(double **, int *, int *); }
using namespace std;
int main()
{
double **array;
int nx=3;
int ny=2;
int i,j;
cout << "Passing dynamic array from C to Fortran\n";
array = (double **) malloc(nx * sizeof(double *));
if(array == NULL)
{
fprintf(stderr, "out of memory\n");
exit;
}
for(i = 0; i < nx; i++)
{
array[i] = (double *) malloc(ny * sizeof(double));
if(array[i] == NULL)
{
fprintf(stderr, "out of memory\n");
exit;
}
}
for(i = 0; i < nx; i++)
{
for(j = 0; j < ny; j++)
{
array[i][j]=i+j+i*(2+j)+4; //random initialisation
cout << "array[" << i << "][" << j << "]=" << array[i][j] << " ";
}
cout << endl;
}
array2d_(array, &nx, &ny);
for(i = 0; i < nx; i++)
free(array[i]);
free(array);
return 0;
}
The fortran side
subroutine array2d(arr,nx_C,ny_C) bind(C,name="array2d_")
use iso_c_binding
implicit none
integer (C_INT), intent(IN) :: nx_C,ny_C !array sizes from C
real (C_DOUBLE), intent(INOUT) :: arr(ny_C,nx_C)
integer :: k,l
print *, "This is in Fortran routine..."
do k = 1,ny_C
do l=1,nx_C
print *, "arr(",k,",",l,") = ", arr(k,l)
end do
end do
end subroutine array2d
The output in C++ is
array[0][0]=4 array[0][1]=5
array[1][0]=7 array[1][1]=9
array[2][0]=10 array[2][1]=13
While in Fortran the output is
arr( 1 , 1 ) = 1.7994937190948764E-305
arr( 1 , 2 ) = 7.1027035167764720E-251
arr( 1 , 3 ) = 9.8813129168249309E-324
arr( 2 , 1 ) = 5.4809152658772852E-317
arr( 2 , 2 ) = 1.5475240269406953E-314
arr( 2 , 3 ) = 0.0000000000000000
So somehow the values are not passed correctly.
The main reason is that your C array is a jagged array, it is an array of pointers to separate 1D arrays while in Fortran you declare ther argument to be a contiguous 2D array. You must use the same in both parts, preferably use a contiguous array in C too.
Just malloc one big nx*ny buffer and set the pointers to the rows instead of alloacating them. You can see an example in https://stackoverflow.com/a/5901671/721644
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