Fortran从C接受字符串(?)

时间:2011-04-10 03:07:24

标签: c++ fortran

我觉得这应该是一个简单的问题,但我无法让它发挥作用。我有一些Fortran代码,它接受如下输入:

      SUBROUTINE TRACE(X,Y,NAME,XX,YY)
      EXTERNAL NAME
      CALL NAME(X,Y,XX,YY)

我试图以C ++的形式传递一个名称:

float x,y,xx,yy;
char * name="IGRF";
trace_(&x,&y,name,&xx,&yy);

它编译,但是当我尝试调用NAME子例程时,我总是得到段错误。在文件中定义了一个名为IGRF的子程序,我可以直接从C ++调用IGRF子程序,但需要这个TRACE例程。在gdb中运行时,它表示NAME变量作为指向void的指针。

我已经尝试传递NAME,& NAME,& NAME [0],一个被剥夺了\ 0的字符名称[4]以完全符合名称,并且它们都返回显示相同的空指针。有人知道如何从C ++中将函数名称转换为Fortran中的EXTERNAL变量吗?

谢谢

4 个答案:

答案 0 :(得分:12)

Fortran2003及更高版本的一个优点是C互操作性定义到标准中;它有点像PITA,但一旦完成,它就可以保证跨平台和编译器工作。

所以这里是cprogram.c,调用Fortran例程getstring

#include <stdio.h>

int main(int argc, char **argv) {
    int l;
    char *name="IGRF";

    l = getstring(name);

    printf("In C: l = %d\n",l);

    return 0;
}

这里是fortranroutine.f90

integer(kind=c_int) function getstring(instr) bind(C,name='getstring') 
    use, intrinsic :: iso_c_binding
    character(kind=c_char), dimension(*), intent(IN) :: instr
    integer :: len
    integer :: i

    len=0
    do
       if (instr(len+1) == C_NULL_CHAR) exit
       len = len + 1
    end do


    print *, 'In Fortran:'
    print *, 'Got string: ', (instr(i),i=1,len)
    getstring = len
end function getstring

makefile非常简单:

CC=gcc
FC=gfortran

cprogram: cprogram.o fortranroutine.o
    $(CC) -o cprogram cprogram.o fortranroutine.o -lgfortran

fortranroutine.o: fortranroutine.f90
    $(FC) -c $^

clean:
    rm -f *.o cprogram *~

并在gcc / gfortran和icc / ifort:

下运行它
 In Fortran:
 Got string: IGRF
In C: l = 4

更新:哦,我刚刚意识到你正在做的事情比传递一个字符串更精细;你本质上是试图传递一个指向C回调例程的函数指针。这是一个小问题,因为你必须使用Fortran interface来声明C例程 - 只使用extern将无法工作(并且无论如何都不如显式接口,因为没有类型检查等。)所以这应该有效:

cprogram.c:

#include <stdio.h>

/* fortran routine prototype*/
int getstring(char *name, int (*)(int));

int square(int i) {
    printf("In C called from Fortran:, ");
    printf("%d squared is %d!\n",i,i*i);
    return i*i;
}


int cube(int i) {
    printf("In C called from Fortran:, ");
    printf("%d cubed is %d!\n",i,i*i*i);
    return i*i*i;
}

int main(int argc, char **argv) {
    int l;
    char *name="IGRF";

    l = getstring(name, &square);
    printf("In C: l = %d\n",l);
    l = getstring(name, &cube);
    printf("In C: l = %d\n",l);


    return 0;
}

froutine.f90:

integer(kind=c_int) function getstring(str,func) bind(C,name='getstring')
    use, intrinsic :: iso_c_binding
    implicit none
    character(kind=c_char), dimension(*), intent(in) :: str
    type(c_funptr), value :: func

    integer :: length
    integer :: i

    ! prototype for the C function; take a c_int, return a c_int
    interface
        integer (kind=c_int) function croutine(inint) bind(C)
            use, intrinsic :: iso_c_binding
            implicit none
            integer(kind=c_int), value :: inint
        end function croutine
    end interface
    procedure(croutine), pointer :: cfun

    integer(kind=c_int) :: clen

    ! convert C to fortran procedure pointer,
    ! that matches the prototype called "croutine"
    call c_f_procpointer(func, cfun)

    ! find string length
    length=0
    do
       if (str(length+1) == C_NULL_CHAR) exit
       length = length + 1
    end do

    print *, 'In Fortran, got string: ', (str(i),i=1,length), '(',length,').'

    print *, 'In Fortran, calling C function and passing length'
    clen = length
    getstring = cfun(clen)

end function getstring

结果:

$ gcc -g -Wall   -c -o cprogram.o cprogram.c
$ gfortran -c fortranroutine.f90 -g -Wall
$ gcc -o cprogram cprogram.o fortranroutine.o -lgfortran -g -Wall
$ gpc-f103n084-$ ./cprogram 
./cprogram 
 In Fortran, got string: IGRF(           4 ).
 In Fortran, calling C function and passing length
In C called from Fortran:, 4 squared is 16!
In C: l = 16
 In Fortran, got string: IGRF(           4 ).
 In Fortran, calling C function and passing length
In C called from Fortran:, 4 cubed is 64!
In C: l = 64

答案 1 :(得分:3)

似乎FORTRAN 77需要指向字符的指针,字符串的长度可以从C ++(或C)传递到FORTRAN。

请参阅this utah.edu document on using C and C++ with FORTRAN,并专门搜索以“CHARACTER * n arguments”开头的文档部分。

答案 2 :(得分:2)

与支持表达式的反射和/或运行时评估的更多动态语言(如python)相反,Fortran,C和C ++不支持。也就是说,没有内置方法将包含过程名称的字符串转换为过程引用并调用它。

也就是说,在您的示例中,NAME需要是指向函数的指针,而不是字符串。通过使用ISO_C_BINDING功能,您可以在C和Fortran之间传递函数指针。

答案 3 :(得分:0)

我也使用了CMake。

的CMakeLists.txt:

cmake_minimum_required(VERSION 3.5)
project(CppFortran C CXX Fortran)

add_executable(CppFortran
    froutine.f90
    main.cpp
    )

的main.cpp

#include <iostream>

extern "C" {
int getString(char *file_name);
}

int main() {
    int l;
    char *name = (char*)"IGRF";

    l = getString(name);
    std::cout << "In C++:"<< std::endl;
    std::cout << "length: " << l << std::endl;

    return 0;
}

froutine.f90

integer(kind=c_int) function getString(instr) bind(C,name='getString')
    use, intrinsic :: iso_c_binding
    character(kind=c_char), dimension(*), intent(IN) :: instr
    integer :: len
    integer :: i

    len=0
    do
        if (instr(len+1) == C_NULL_CHAR) exit
        len = len + 1
    end do

    print *, 'In Fortran:'
    print *, 'Got string: ', (instr(i),i=1,len)
    getstring = len
end function getString

控制台输出:

 In Fortran:
 Got string: IGRF
In C++:
length: 4