将char数组从c ++传递到fortran [英] passing char arrays from c++ to fortran

问题描述

我无法将字符数组从c ++传递到fortran（f90）。

这是我的c ++文件'cmain.cxx'：

  #include< iostream> 
 
 using namespace std; 
 
 externCint ftest_（char（* string）[4]）; 
 
 int main（）{
 char string [2] [4]; 
 
 strcpy（string [0]，abc）; 
 strcpy（string [1]，xyz）; 
 
 cout<< c ++：string [0] ='< string [0]<< '< endl 
 cout<< c ++：string [1] ='< string [1]< '< endl 
 
 ftest_（string）; 
 
 return 0; 
} 
  

这里是我的fortran文件，'ftest.f90'：

  SUBROUTINE FTEST（字符串）
 
 CHARACTER * 3字符串（2）
 CHARACTER * ）
预期数据（1）/'abc'/ 
预期数据（2）/'xyz'/ 
 
 DO i = 1,2 
 WRITE ，10）i，string（i）
 10 FORMAT（fortran：string（，i1，）='，a，' ）.eq.expected（i））THEN 
 WRITE（6,20）string（i），expected（i）
 20 FORMAT（'，a，'equals' '）
 ELSE 
 WRITE（6,30）string（i），expected（i）
 30 FORMAT（'，a，'不等于' ，'）
 END IF 
 ENDDO 
 
 RETURN 
 END 
  

构建过程是：

  gfortran -c -m64 ftest.f90 
 g ++ -c cmain.cxx 
 gfortran -m64 -lstdc ++ -gnofor_main -o test ftest.o cmain.o 
  

编辑：请注意，可执行文件也可以通过以下方式构建：

  g ++ -lgfortran -o test ftest.o cmain.o 
  

此外，运行OSX 10.6时需要-m64标志。

执行'test'的输出是：

  c ++：string [0 ] ='abc'
 c ++：string [1] ='xyz'
 fortran：string（1）='abc'
'abc' string（2）='xy'
'xy'不等于'xyz'
  

在size为4的ftest.f90中声明'string'和'expected'字符数组，即：

  CHARACTER * 4 string 2）
 CHARACTER * 4 expected（2）
  

并且重新编译给出以下输出： / p>

  c ++：string [0] ='abc'
 c ++：string [1] ='xyz'
 fortran：string（1）='abc'
'abc'不等于'abc'
 fortran：string（2）='xyz'
'xyz'不等于'xyz '
  

在cmain.cxx中声明大小为3的字符数组，即：

  externCint ftest_（char（* string）[3]）; 
 
 int main（）{
 char string [2] [3]; 
  

并恢复到fortran文件中的原始大小（3），即：

  CHARACTER * 3 string（2）
 CHARACTER * 3 expected（2）
  pre> 
 
 
并且重新编译提供以下输出：
  c ++：string [0] ='abcxyz'
 c ++：string [1] ='xyz'
 fortran：string（1）='abc'
'abc'equals'abc'
 fortran：string（2）='xyz'
'xyz'等于'xyz'
  
所以最后一种情况是唯一一个工作，但在这里我已经分配了3个字符大小为3的字符数组，这意味着终止'\0'缺失，并导致'abcxyz'输出 - 这是不可接受的为我的预期应用。 
 
 
 
任何帮助将非常感谢，这是我的坚果！
解决方案
 C字符串是零终止，而fortran字符串，按照惯例，是空格填充，但固定大小。 
 
 
 
例如：
  #include< algorithm> 
 
 void ConvertToFortran（char * fstring，std :: size_t fstring_len，
 const char * cstring）
 {
 std :: size_t inlen = std :: strlen cstring）; 
 std :: size_t cpylen = std :: min（inlen，fstring_len）; 
 
 if（inlen> fstring_len）
 {
 // TODO：truncation error or warning 
} 
 
 std :: copy cstring，cstring + cpylen，fstring）; 
 std :: fill（fstring + cpylen，fstring + fstring_len，''）; 
} 
  
然后您可以使用3或4长度版本的 ftest ：
  #include< iostream> 
 #include< ostream> 
 externCint ftest_（char string [] [4]）; 
 
 void ConvertToFortran（char * fstring，std :: size_t fstring_len，
 const char * cstring）; 
 
 int main（）
 {
 char cstring [2] [4] = {abc，xyz}; 
 char string [2] [4]; 
 
 ConvertToFortran（string [0]，sizeof string [0]，cstring [0]）; 
 ConvertToFortran（string [1]，sizeof string [1]，cstring [1]）; 
 
 std :: cout<< c ++：string [0] ='< cstring [0]<< '< std :: endl; 
 std :: cout<< c ++：string [1] ='< cstring [1]<< '< std :: endl; 
 
 ftest_（string）; 
 
 return 0; 
} 
  
 
I am having trouble passing char arrays from c++ to fortran (f90).

Here is my c++ file, 'cmain.cxx':
#include <iostream>

using namespace std;

extern "C" int ftest_( char (*string)[4] );

int main() {
    char string[2][4];

    strcpy(string[0],"abc");
    strcpy(string[1],"xyz");

    cout << "c++: string[0] = '" << string[0] << "'" << endl;
    cout << "c++: string[1] = '" << string[1] << "'" << endl;

    ftest_(string);

    return 0;
}
Here is my fortran file, 'ftest.f90':
SUBROUTINE FTEST(string)

CHARACTER*3 string(2)
CHARACTER*3 expected(2)
data expected(1)/'abc'/
data expected(2)/'xyz'/

DO i=1,2
    WRITE(6,10) i,string(i)
10  FORMAT("fortran: string(",i1,") = '", a, "'" )

    IF(string(i).eq.expected(i)) THEN
        WRITE(6,20) string(i),expected(i)
20      FORMAT("'",a,"' equals '",a,"'")
    ELSE
        WRITE(6,30) string(i),expected(i)
30      FORMAT("'",a,"' does not equal '",a,"'")
    END IF
ENDDO

RETURN
END
The build process is:
gfortran -c -m64   ftest.f90 
g++ -c  cmain.cxx
gfortran -m64 -lstdc++ -gnofor_main -o test ftest.o cmain.o
Edit: note that the executable can also be build via:
g++ -lgfortran -o test ftest.o cmain.o
Also, the -m64 flag is required as I am running OSX 10.6.

The output from executing 'test' is:
c++: string[0] = 'abc'
c++: string[1] = 'xyz'
fortran: string(1) = 'abc'
'abc' equals 'abc'
fortran: string(2) = 'xy'
'xy' does not equal 'xyz'
Declaring the 'string' and 'expected' character arrays in ftest.f90 with size 4, ie:
CHARACTER*4 string(2)
CHARACTER*4 expected(2)
and recompiling gives the following output:
c++: string[0] = 'abc'
c++: string[1] = 'xyz'
fortran: string(1) = 'abc'
'abc' does not equal 'abc '
fortran: string(2) = 'xyz'
'xyz' does not equal 'xyz '
Declaring the character arrays in 'cmain.cxx' with size 3, ie:
extern "C" int ftest_( char (*string)[3] );

int main() {
    char string[2][3];
and reverting to the original size in the fortran file (3), ie:
CHARACTER*3 string(2)
CHARACTER*3 expected(2)
and recompiling gives the following output:
c++: string[0] = 'abcxyz'
c++: string[1] = 'xyz'
fortran: string(1) = 'abc'
'abc' equals 'abc'
fortran: string(2) = 'xyz'
'xyz' equals 'xyz'
So the last case is the only one that works, but here I have assigned 3 characters to a char array of size 3 which means the terminating '\0' is missing, and leads to the 'abcxyz' output - this is not acceptable for my intended application.  

Any help would be greatly appreciated, this is driving me nuts!
解决方案
C strings are zero terminated whereas fortran strings, by convention, are space padded but of fixed size. You shouldn't expect to be able to pass C strings to fortran without some conversion.

For example:
#include <algorithm>

void ConvertToFortran(char* fstring, std::size_t fstring_len,
                      const char* cstring)
{
    std::size_t inlen = std::strlen(cstring);
    std::size_t cpylen = std::min(inlen, fstring_len);

    if (inlen > fstring_len)
    {
        // TODO: truncation error or warning
    }

    std::copy(cstring, cstring + cpylen, fstring);
    std::fill(fstring + cpylen, fstring + fstring_len, ' ');
}
Which you can then use with either the 3 or 4 length version of ftest:
#include <iostream>
#include <ostream>
extern "C" int ftest_( char string[][4] );

void ConvertToFortran(char* fstring, std::size_t fstring_len,
                      const char* cstring);

int main()
{
    char cstring[2][4] = { "abc", "xyz" };
    char string[2][4];

    ConvertToFortran(string[0], sizeof string[0], cstring[0]);
    ConvertToFortran(string[1], sizeof string[1], cstring[1]);

    std::cout << "c++: string[0] = '" << cstring[0] << "'" << std::endl;
    std::cout << "c++: string[1] = '" << cstring[1] << "'" << std::endl;

    ftest_(string);

    return 0;
}


                        
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