How to initialize a structure variable in a C++ header file using Python ctypes?

I am trying to intialize the structure ExternalInputs_add_two in .h header file using Python ctypes. The header file is:

typedef struct {  
    int32_T Input;                       /* '<Root>/Input' */  
    int32_T Input1;                      /* '<Root>/Input1' */  
} ExternalInputs_add_two;  

I need to initialize this structure since this member declaration uses the structure values for input:

extern ExternalInputs_add_two add_two_U;  

What ctypes function intializes the structure? My Python code so far is:

class ModelOutput(Structure):  
    _fields_ = [("Output", c_int)]  

class ModelInput(Structure):  
    _fields_ = [("Input", c_int),  
                ("Input1", c_int)]  


#define the functions      
initiateModel = cdll.add_two_win32.add_two_initialize  
stepModel = cdll.add_two_win32.add_two_step  
terminateModel = cd开发者_开发技巧ll.add_two_win32.add_two_terminate  


#define the pointers to the functions  
initiateModel.restype = c_void_p  
stepModel.restype = c_void_p  
terminateModel.restype = c_void_p  

#initialize the model with value of 1  
print "\n\nInitialize"  
errMsg = initiateModel(1)  
print "initateModel reports:", errMsg  

#Set the input  
test_input = ModelInput(1,2)    
input_ptr =  pointer(test_input)  

#This probably doesn't work since ExternalInputs_add_two is a structure, not a function.  
cdll.add_two_win32.ExternalInputs_add_two = input_ptr  

#Get the output pointer from add_two_U  
output = POINTER(ModelOutput)  
results = output.in_dll(cdll.add_two_win32,"add_two_U")  

print "got results", results.Output  

I asked the question yesterday how to get the output from the member add_two_U. David was nice enough to answer this question yesterday (use the in_dll function).

I've searched the ctypes documentation and online for an example or function to set a structure using ctype. I haven't found any so far.

Thank you for your help.

Thank you for your help and answer. Unfortunately, setting the input structure this way does not work. I forgot to mention that a Matlab script was written to use the dll and it works. I'm trying to convert to Python. To initialize the structure ExternalInputs_add_two, Matlab uses the following statements:

sm.Input = 1  
sm.Input1 = 2  
sp = libpointer('ExternalInputs_add_two', sm)   

Then function add_two_U is called:

sp = calllib('add_two_win32', 'add_two_U')  
sp.value  
get(sp, 'Value')  
sp.Value.Input = 3  
sp.Value.Input1 = 2  

If I remove the Matlab statement that initializes the ExternalInputs_add_two structure, I get an error.

What is the Python ctypes equivalent to initialize the structure? I'm sorry if I seem to be a pest.

It seems that you're confusing structure definitions with structure instances. As declared in the header file, ExternalInputs_add_two is a type and add_two_U is an instance. DLLs do not export types, only instances of types. Thus the following line in your Python code is nonsensical:

cdll.add_two_win32.ExternalInputs_add_two = input_ptr

What you probably want instead is to modify the instance of ExternalInputs_add_two called add_two_U. To do this, you do as David's previous answer suggested and use the in_dll function:

PModelInput= POINTER(ModelInput)
padd_two_U = PModelInput.in_dll(cdll.add_two_win32, "add_two_U")

# Now modify the contents of the "add_two_U" variable
padd_two_U.Input = 1
padd_two_U.Input2 = 2

My advice to you is to stop exporting the variable from the DLL. Instead you should export two functions from your DLL: one to read the variable, and one to write the variable.