Question

我正在尝试使用ctypes在Python 2.7中加载DLL。 DLL是使用Fortran编写的，并且有多个子例程。我能够成功设置一些导出的函数，long和double指针作为参数。

import ctypes as C
import numpy as np

dll = C.windll.LoadLibrary('C:\\Temp\\program.dll')
_cp_from_t = getattr(dll, "CP_FROM_T")
_cp_from_t.restype = C.c_double
_cp_from_t.argtypes = [C.POINTER(C.c_longdouble),
                    np.ctypeslib.ndpointer(C.c_longdouble)]

# Mixture Rgas function
_mix_r = getattr(dll, "MIX_R")
_mix_r.restype = C.c_double
_mix_r.argtypes = [np.ctypeslib.ndpointer(dtype=C.c_longdouble)]

def cp_from_t(composition, temp):
    """ Calculates Cp in BTU/lb/R given a fuel composition and temperature.

    :param composition: numpy array containing fuel composition
    :param temp: temperature of fuel
    :return: Cp
    :rtype : float
    """
    return _cp_from_t(C.byref(C.c_double(temp)), composition)

def mix_r(composition):
    """Return the gas constant for a given composition.
    :rtype : float
    :param composition: numpy array containing fuel composition
    """
    return _mix_r(composition)

# At this point, I can just pass a numpy array as the composition and I can get the 
# calculated values without a problem
comps = np.array([0, 0, 12.0, 23.0, 33.0, 10, 5.0])
temp = 900.0

cp = cp_from_t(comps, temp)
rgas = mix_r(comps)

到目前为止，非常好。

当我尝试另一个名为Function2的子例程需要一些字符串作为输入时，会出现问题。字符串都是固定长度（255），它们还要求每个字符串参数的长度。

该功能在Fortran中实现如下：

Subroutine FUNCTION2(localBasePath,localTempPath,InputFileName,Model,DataArray,ErrCode)
!DEC$ ATTRIBUTES STDCALL,REFERENCE, ALIAS:'FUNCTION2',DLLEXPORT :: FUNCTION2
Implicit None
Character *255 localBasePath,localTempPath,InputFileName
Integer   *4  Model(20), ErrCode(20)
Real      *8  DataArray(900)

Python中的函数原型设置如下

function2 = getattr(dll, 'FUNCTION2')
function2.argtypes = [C.POINTER(C.c_char_p), C.c_long,
                      C.POINTER(C.c_char_p), C.c_long,
                      C.POINTER(C.c_char_p), C.c_long,
                      np.ctypeslib.ndpointer(C.c_long , flags='F_CONTIGUOUS'),
                      np.ctypeslib.ndpointer(C.c_double, flags='F_CONTIGUOUS'),
                      np.ctypeslib.ndpointer(C.c_long, flags='F_CONTIGUOUS')]

我用它来称呼它：

base_path = "D:\\Users\\xxxxxxx\\Documents\\xxxxx\\".ljust(255)
temp_path = "D:\\Users\\xxxxxxx\\Documents\\xxxxx\\temp".ljust(255)
inp_file = "inp.txt".ljust(255)

function2(C.byref(C.c_char_p(base_path)),
                  C.c_long(len(base_path)),
                  C.byref(C.c_char_p(temp_dir)),
                  C.c_long(len(temp_dir))),
                  C.byref(C.c_char_p(inp_file)),
                  C.c_long(len(inp_file)),
                  model_array,
                  data_array,
                  error_array)

字符串本质上是路径。函数Function2无法识别路径并证明最后带有一些不可读字符的错误消息，例如：

forrtl: severe (43): file name specification error, unit 16, D:\Users\xxxxxxx\Documents\xxxxx\œâa。

我想要接收的功能是D:\Users\xxxxxxx\Documents\xxxxx\。显然，字符串没有正确传递。

我已经读过Python使用NULL终止的字符串。将字符串传递给Fortran DLL时可能会出现问题吗？如果是这样，我该如何解决它？

有什么建议吗？

Answer 1

在@eryksun发表评论后，我进行了以下更改以使其正常运行。

将argtypes更改为：

function2 = getattr(dll, 'FUNCTION2')
function2.argtypes = [C.c_char_p, C.c_long,
                  C.c_char_p, C.c_long,
                  C.c_char_p, C.c_long,
                  np.ctypeslib.ndpointer(C.c_long , flags='F_CONTIGUOUS'),
                  np.ctypeslib.ndpointer(C.c_double, flags='F_CONTIGUOUS'),
                  np.ctypeslib.ndpointer(C.c_long, flags='F_CONTIGUOUS')]

而不是将字符串作为byref传递，我将其更改为以下内容。

base_path = "D:\\Users\\xxxxxxx\\Documents\\xxxxx\\".ljust(255)
temp_path = "D:\\Users\\xxxxxxx\\Documents\\xxxxx\\temp".ljust(255)
inp_file = "inp.txt".ljust(255)

function2(base_path, len(base_path), temp_dir, len(temp_dir), inp_file, len(inp_file), 
          model_array, data_array, error_array)

直接传递值就足够了。

使用ctypes和Python将字符串传递给Fortran DLL

1 个答案: