python - 有问题的字符串参数 ctypes python 与 C 代码

Question

我正在为 C 代码编写一个包装器。我为代码提供了不同的选项，除了第三个参数外，一切都很好。第三个参数是一个指向文件的指针。我通过编码python的字符串（path_to_log_file）来编组数据。但是，当它不起作用时，这第三个参数应该将 shell 的输出流重定向到日志文件。我得到的结果是一个像这样的奇怪文件， 我想我遗漏了一些东西，但我不明白出了什么问题，因为我对字符串进行了编码。C函数签名：

int lisaf_phasemeter_main(int argc, char* argv[], const char *LogFileName) 

驱动代码：

#%% Module import
import signal
import ctypes
import os
import sys
import json
import multiprocessing
#%% Constant definition.

# Driver accepted options 
ACCEPTED_DRIVER_ARGS=["logfile"]

# C_Code accepted options 
ACCEPTED_ARGS = ["erase","binary","help","intclk"]
ACCEPTED_KWARGS= ["fsampling","comment","trun","vcal"]

# Opening config file object and creating dictionnary object to parse it
PATH_TO_CONFIG_FILE="config/Config.json"
ConfigFile = open(PATH_TO_CONFIG_FILE, "r")
jsonContent = ConfigFile.read()
Config = json.loads(jsonContent)

# Driver's name
PROGRAM_NAME=str(__file__)

# Configuring signal to enable interuption of C_Code
signal.signal(signal.SIGINT,signal.SIG_DFL)



#%% Class definiton
class Phasemeter :
    """ This class is a driver for LISA Phasemeters data acquisiton """
    # List of all phasemeters objects
    phase_list=[]

    def __init__(self,name="PH1") :
        """ This method define path, enables interuptions of C code and defines
            C code signature
            TODO : Paralelization
        """
        self.name = name

        # Path to driver configuration File
        self.path_to_cfg_file=Config[self.name]["PATH_TO_CFG_FILE"]

        # Path to data File
        self.path_to_data_file=Config[self.name]["PATH_TO_DATA_FILE"]

        # Path to log file
        self.path_to_log_file=Config[self.name]["PATH_TO_LOG_FILE"]

        # Path to Shared Object File. Shared Object (SO) File is the output
        # of C code used by this program to use the C Code.
        self.path_to_so_file=Config[self.name]["PATH_TO_SO_FILE"]
        self.so_namefile=Config[self.name]["SO_NAMEFILE"]


        # Defining path to shared object file
        self.path=os.path.abspath(os.path.join(os.getcwd(),
                                               self.path_to_so_file))
        self.libname = self.so_namefile
        self.LIBC = ctypes.CDLL(os.path.join(self.path,self.libname))

        # Settings C library's signature datatype
        self.LIBC.lisaf_phasemeter_main.argtypes= [ctypes.c_int,
                                            ctypes.POINTER(ctypes.c_char_p),
                                            ctypes.POINTER(ctypes.c_char_p),]

        self.LIBC.lisaf_phasemeter_main.restypes = [ctypes.c_int,]

        Phasemeter.phase_list.append(self)
        print(Phasemeter.phase_list)



    def start(self,*args,**kwargs):
        """ This method starts acquisition for the Phasemeter. It handles
        options and launches the Phasemeter's C code for acquisiiton.
        -----------------------------------------------------------------------

        Simple arguments :

        (str)   erase: Erase previous Data file without asking permission
                (default is off)
                -> my_phasemeter.start("erase")

        (str)   binary: Change output format to binary (default is txt)
                -> my_phasemeter.start("binary")

        (str)   intclk: Call internal clock (unstable)
                -> my_phasemeter.start("intclk")

        (str)   help: Call c code's help (not very usefull to use the wrapper)
                -> my_phasemeter.start("help")

    Keywords arguments :

        (int)   fsampling: Sampling frequency (default is 0.0)
        (float) -> my_phasemeter.start(fsampling=#value)

        (int)   vcal: Calibration Voltage (default is 0.0)
        (float) -> my_phasemeter.start(vcal=#value)

        (int)   trun: Specify acquisition time,any negative results in infinite
        (float) acquisition time (default is 0.0)
                -> my_phasemeter.start(trun=#your_value)

        (str)   comment: Add a comment to the data file's header
                -> my_phasemeter.start(comment="#your_comment")

        -----------------------------------------------------------------------
        Method call examples
                    : my_phasemeter.start()
                    : my_phasemeter.start("erase",fsampling=100,trun=50,
                                           comment="Test")
                    : my_phasemeter.start("help")
                    : my_phasemeter.start("intclk","erase",comment="Test",
                                           fsampling=100,trun=100,vcal=2)
        -----------------------------------------------------------------------
            """
        self.log_flag= False
        # Robustness

        # Checkings simple arguments
        for argument in args :
            # Checking if args are string type
            if type(argument) is not str :
                sys.tracebacklimit = 0
                raise TypeError("Wrong type for argument ",argument,
                                ", only strings are authorized")
        # Checking keywords argument
        for argument in kwargs :
            if argument in ["fsampling","vcal"] and int(kwargs[argument]) < 0 :
                raise ValueError('Please enter a positive number for keyword ',
                                                                     argument)
            if argument in ["comment","logfile"] and type(kwargs[argument]) is not str :
                raise TypeError
                ("Please enter a string for keyword argument",argument)

        # Changing data structure to fit Marshalling

    # Here we want to mimic C code's argv

        # Storing valid arguments
        args_list=[]

        # Storing non transmited arguments
        ignored_args=[]

        # Adding core arguments
        args_list.append(PROGRAM_NAME)
        args_list.append(self.path_to_cfg_file)
        args_list.append(self.path_to_data_file)

        # Handling optionnal arguments
        for argument in args :
            if argument in ACCEPTED_ARGS :
                args_list.append(str("--"+str(argument)))
            elif argument == "logfile":
                self.log_flag = True
            else :
                ignored_args.append(argument)

        for argument in kwargs :
            if argument in ACCEPTED_KWARGS :
                args_list.append(str("--"+str(argument)))
                args_list.append(str(kwargs[argument]))
            else :
                ignored_args.append(argument)

        # Expanding the argument list to mimic a C array
        options=[*args_list]

        # Debug
        print("Options transmitted to C Code : ",*options)
        if ignored_args:
            print("Ignored given options : ",*ignored_args)
            if "logfile" in ignored_args:
                print("Logfile option activated")

        # Marshalling data for C library
        self.c_char_pointer_array = ctypes.c_char_p * len(options)
        self.encoded_options = [str.encode(str(i)) for i in options ]
        self.encoded_options = self.c_char_pointer_array (*self.encoded_options)

        # If Logfile option activated we encode the path to the log file 
        if self.log_flag :
            self.c_char_pointer_array = ctypes.c_char_p * 1
            self.encoded_path_to_log_file = [str.encode(self.path_to_log_file)]
            self.encoded_path_to_log_file = self.c_char_pointer_array (*self.encoded_path_to_log_file)

        # Calling C library wihth encoded options
    # If the logfile option is activated then the encoded string is transmited
        if self.log_flag :
            self.status = self.LIBC.lisaf_phasemeter_main(len(self.encoded_options),
                                                      self.encoded_options,self.encoded_path_to_log_file)
       # Otherwise None pointer is transmited
        else :
            self.status = self.LIBC.lisaf_phasemeter_main(len(self.encoded_options),
                                                      self.encoded_options,None)

标签： pythonctypes

Answer 1

As Dan said

the issue is the code passes a char** argument to a function that takes a char * parameter

So I figured how to fix this mistake by changing two things :

1. The signature of the C function in the Python code :

   self.LIBC.lisaf_phasemeter_main.argtypes=[ctypes.c_int,ctypes.POINTER(ctypes.c_char_p),ctypes.c_char_p,]

2. The data structure passed to the C function

   if "logfile" in args : self.encoded_path_to_log_file = str.encode(self.path_to_log_file)

Full code :

    #%% Module import
    import signal
    import ctypes
    import os
    import sys
    import json
    import multiprocessing
    #%% Constant definition.
    
    # Driver accepted options 
    ACCEPTED_DRIVER_ARGS=["logfile"]
    
    # C_Code accepted options 
    ACCEPTED_ARGS = ["erase","binary","help","intclk"]
    ACCEPTED_KWARGS= ["fsampling","comment","trun","vcal"]
    
    # Opening config file object and creating dictionnary object to parse it
    PATH_TO_CONFIG_FILE="config/Config.json"
    ConfigFile = open(PATH_TO_CONFIG_FILE, "r")
    jsonContent = ConfigFile.read()
    Config = json.loads(jsonContent)
    
    # Driver's name
    PROGRAM_NAME=str(__file__)
    
    # Configuring signal to enable interuption of C_Code
    signal.signal(signal.SIGINT,signal.SIG_DFL)
    
    
    
    #%% Class definiton
    class Phasemeter :
        """ This class is a driver for LISA Phasemeters data acquisiton """
        # List of all phasemeters objects
        phase_list=[]
    
        def __init__(self,name="PH1") :
            """ This method define path, enables interuptions of C code and defines
                C code signature
                TODO : Paralelization
            """
            self.name = name
    
            # Path to driver configuration File
            self.path_to_cfg_file=Config[self.name]["PATH_TO_CFG_FILE"]
    
            # Path to data File
            self.path_to_data_file=Config[self.name]["PATH_TO_DATA_FILE"]
    
            # Path to log file
            self.path_to_log_file=Config[self.name]["PATH_TO_LOG_FILE"]
    
            # Path to Shared Object File. Shared Object (SO) File is the output
            # of C code used by this program to use the C Code.
            self.path_to_so_file=Config[self.name]["PATH_TO_SO_FILE"]
            self.so_namefile=Config[self.name]["SO_NAMEFILE"]
    
    
            # Defining path to shared object file
            self.path=os.path.abspath(os.path.join(os.getcwd(),
                                                   self.path_to_so_file))
            self.libname = self.so_namefile
            self.LIBC = ctypes.CDLL(os.path.join(self.path,self.libname))
    
            # Settings C library's signature datatype
            self.LIBC.lisaf_phasemeter_main.argtypes= [ctypes.c_int,
                                                ctypes.POINTER(ctypes.c_char_p),
                                                ctypes.c_char_p,]
    
            self.LIBC.lisaf_phasemeter_main.restypes = [ctypes.c_int,]
    
            Phasemeter.phase_list.append(self)
            print(Phasemeter.phase_list)
    
    
    
        def start(self,*args,**kwargs):
            """ This method starts acquisition for the Phasemeter. It handles
            options and launches the Phasemeter's C code for acquisiiton.
            -----------------------------------------------------------------------
    
            Simple arguments :
    
            (str)   erase: Erase previous Data file without asking permission
                    (default is off)
                    -> my_phasemeter.start("erase")
    
            (str)   binary: Change output format to binary (default is txt)
                    -> my_phasemeter.start("binary")
    
            (str)   intclk: Call internal clock (unstable)
                    -> my_phasemeter.start("intclk")
    
            (str)   help: Call c code's help (not very usefull to use the wrapper)
                    -> my_phasemeter.start("help")
    
            (str)   logfile : Redirect the shell output to a log file 
                    -> my_phasemeter.start("logfile")
    
            Keywords arguments :
    
            (int)   fsampling: Sampling frequency (default is 0.0)
            (float) -> my_phasemeter.start(fsampling=#value)
    
            (int)   vcal: Calibration Voltage (default is 0.0)
            (float) -> my_phasemeter.start(vcal=#value)
    
            (int)   trun: Specify acquisition time,any negative results in infinite
            (float) acquisition time (default is 0.0)
                    -> my_phasemeter.start(trun=#your_value)
    
            (str)   comment: Add a comment to the data file's header
                    -> my_phasemeter.start(comment="#your_comment")
    
            -----------------------------------------------------------------------
            Method call examples
                        : my_phasemeter.start()
                        : my_phasemeter.start("erase",fsampling=100,trun=50,
                                               comment="Test")
                        : my_phasemeter.start("help")
                        : my_phasemeter.start("intclk","erase",comment="Test",
                                               fsampling=100,trun=100,vcal=2)
            -----------------------------------------------------------------------
                """
    
            # Robustness
    
            # Checkings simple arguments
            for argument in args :
                # Checking if args are string type
                if type(argument) is not str :
                    sys.tracebacklimit = 0
                    raise TypeError("Wrong type for argument ",argument,
                                    ", only strings are authorized")
            # Checking keywords argument
            for argument in kwargs :
                if argument in ["fsampling","vcal"] and int(kwargs[argument]) < 0 :
                    raise ValueError('Please enter a positive number for keyword ',
                                                                         argument)
                if argument in ["comment","logfile"] and type(kwargs[argument]) is not str :
                    raise TypeError
                    ("Please enter a string for keyword argument",argument)
    
            # Changing data structure to fit Marshalling
    
        # Here we want to mimic C code's argv
    
            # Storing valid arguments
            args_list=[]
    
            # Storing non transmited arguments
            ignored_args=[]
    
            # Adding core arguments
            args_list.append(PROGRAM_NAME)
            args_list.append(self.path_to_cfg_file)
            args_list.append(self.path_to_data_file)
    
            # Handling optionnal arguments
            for argument in args :
                if argument in ACCEPTED_ARGS :
                    args_list.append(str("--"+str(argument)))
                elif argument == "logfile" :
                else :
                    ignored_args.append(argument)
    
            for argument in kwargs :
                if argument in ACCEPTED_KWARGS :
                    args_list.append(str("--"+str(argument)))
                    args_list.append(str(kwargs[argument]))
                else :
                    ignored_args.append(argument)
    
            # Expanding the argument list to mimic a C array
            options=[*args_list]
    
            # Debug
            print("Options transmitted to C Code : ",*options)
            if ignored_args:
                print("Ignored given options : ",*ignored_args)
    
            # Verbose
            if "logfile" in args:
                print("Logfile option activated, logs going to : ", self.path_to_log_file)
    
            # Marshalling data for C library
            self.c_char_pointer_array = ctypes.c_char_p * len(options)
            self.encoded_options = [str.encode(str(i)) for i in options ]
            self.encoded_options = self.c_char_pointer_array (*self.encoded_options)
    
            # If Logfile option activated we encode the path to the log file 
            if "logfile" in args  :
                self.encoded_path_to_log_file = str.encode(self.path_to_log_file)
    
            # Calling C library wihth encoded options
        # If the logfile option is activated then the encoded string is transmited
            if "logfile" in args :
                self.status = self.LIBC.lisaf_phasemeter_main(len(self.encoded_options),
                                                          self.encoded_options,self.encoded_path_to_log_file)
           # Otherwise None pointer is transmited
            else :
                self.status = self.LIBC.lisaf_phasemeter_main(len(self.encoded_options),
                                                          self.encoded_options,None)