Fortran向C傳遞NULL值

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在很多C或C++的頭文件定義中，NULL被指定定義為0，這里不再具體展開

gfortran的手冊關于iso c binding的章節，定義NULL如下

Moreover, the following two named constants are defined:

Name	Type?
C_NULL_PTR	C_PTR
C_NULL_FUNPTR	C_FUNPTR

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Both are equivalent to the value?NULL?in C.

據此，從Fortran向C或C++傳遞空指針還是需要一些技巧，也即需要把傳入參數設置為指針類型C_PTR

接下來是代碼：

#include "stdio.h"int test(int *a, int num)
{if(!a){printf("This is null pointer\n");}else{for(int i=0; i<num; i++){printf("Array[%d]=%d\n", i+1, a[i]);}}return 0;
}

program main
use, intrinsic:: iso_c_binding
implicit none
interfaceinteger(c_int) function func(array, n) bind(c, name="test")importimplicit noneinteger(c_int), intent(in), value:: ninteger(c_int), intent(in):: array(n)end functioninteger(c_int) function func2(pt, n) bind(c, name="test")importimplicit noneinteger(c_int), intent(in), value:: ntype(c_ptr), value:: ptend function
end interfacetype(c_ptr) :: a1
integer(c_int), target:: abc(5)
integer:: iabc = [12, 12, 35, 67, 11]
a1 = c_loc(abc(1))
! Pass array directly
i = func(abc, size(abc))
! Pass address
i = func2(c_loc(abc(1)), 5)
! Pass null pointer
i = func2(c_null_ptr, 5)
! Pass null function pointer
i = func2(c_null_funptr, 5)
end program

gfortran code_c.c code_for.f90 -o test

運行結果：

Array[1]=12
Array[2]=12
Array[3]=35
Array[4]=67
Array[5]=11

Array[1]=12
Array[2]=12
Array[3]=35
Array[4]=67
Array[5]=11

This is null pointer

This is null pointer

　　

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