passing a single character/multiple character user input from a python function to a C++ function

Question

I have a C++ .dll function that I am accessing through python 3.2 with the syntax:

int Create(char argID)

and I am trying to access this function using python. I can access it, but I am confused on why it is telling for 'wrong type' whenever I try to pass the function an argument. Python Script:

Create.argtypes = [c_char]
Create.restype = c_int
ID = c_char
ID = input("Enter ID:")
Create(ID) #ctypes.ArgumentError: argument 1: <class 'TypeError'>: wrong type

Not sure where I am going wrong or is there a different way to pass a character or characters from the user input? Kindly help.

Cheers.

I am working on python version 3.2. raw_input() is replaced by input(). — Neophile
– Neophile, Commented Sep 16, 2011 at 9:00

Eryk Sun · Accepted Answer · 2011-09-16 10:57:38Z

2

A c_char is a one-byte value, not a Unicode string. Set ID = bytes(ID, 'utf8')[0] (or use a different 8-bit character mapping than 'utf8', such as 'latin-1'). Then you can call Create(ID).

By the way, assigning ID to c_char only gives you another reference to c_char, and then you immediately reassign ID to the returned string from input. The only time I see this is when people are working with ctypes. It's like the brain gets stuck in static typing mode.

answered Sep 16, 2011 at 10:57

Eryk Sun

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3 Comments

Neophile Over a year ago

By the way I am using ctypes because of the fact that I am accessing a C++ dll from Python. I tried your way and I am not getting any errors, but the Create function is not being executed because ID now has a value(66) instead of a character('B'). Since my C++ function accepts a character, what would you suggest?

Neophile Over a year ago

Very helpful information :). Just another question in the same context, how do we do the same for a string of characters? Thanks again for your answer. It works now.

Neophile Over a year ago

Thanks a lot. +1 from my side :). You have been really helpful.

MatthieuW · Accepted Answer · 2011-09-16 09:12:00Z

0

Your Create function accept a single char as argument, not a string.

s = input("enter ID:")
c = ctypes.c_char(s[0])
Create(c)

edited Sep 16, 2011 at 9:12

answered Sep 16, 2011 at 8:50

MatthieuW

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3 Comments

Neophile Over a year ago

Yes certainly. But I just input one character as an input. Does it read as a string? If so, what is the equivalent command so that it could read a single character?

Léo Germond Over a year ago

I think the ID name implies it is some sort of numeric value converted as a char, then you should use s = int(input("Enter ID")) c = ctypes.c_char(chr(s)) Edit: Formatting is a bitch

Neophile Over a year ago

@ Leo: No, it is a single character input and not a numeric value. Something like 'a', 'b' etc. @MatthieuW: It did not work the way you suggested via the code. Same error again.

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