create_string_buffer throws a TypeError error: str / bytes expected in place of...
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create_string_buffer throws a TypeError error: str / bytes expected in place of the str instance
I am trying this simple ctypes example and getting the error mentioned
>>> from ctypes import create_string_buffer
>>> str = create_string_buffer("hello")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Python32\lib\ctypes\__init__.py", line 59, in create_string_buffer
buf.value = init
TypeError: str/bytes expected instead of str instance
Does anyone know what am I doing wrong?
On the same note, I am trying to pass a pointer to a string to a C function from my python code so that I can perform some string operation there and return another string. Can someone give me some sample code on how to do that?
extern "C" __declspec(dllexport) char * echo(char* c)
{
// do stuff
return c;
}
With regards to getting it working, if you pass it a bytes
object, it works:
>>> import ctypes
>>> ctypes.create_string_buffer(b'hello')
<ctypes.c_char_Array_6 object at 0x25258c0>
Looking at the code for create_string_buffer
:
def create_string_buffer(init, size=None):
"""create_string_buffer(aBytes) -> character array
create_string_buffer(anInteger) -> character array
create_string_buffer(aString, anInteger) -> character array
"""
if isinstance(init, (str, bytes)):
if size is None:
size = len(init)+1
buftype = c_char * size
buf = buftype()
buf.value = init
return buf
elif isinstance(init, int):
buftype = c_char * init
buf = buftype()
return buf
raise TypeError(init)
Doing it directly,
>>> (ctypes.c_char * 10)().value = b'123456789'
This works fine.
>>> (ctypes.c_char * 10)().value = '123456789'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: str/bytes expected instead of str instance
This shows that same behaviour. Looks to me as though you've found a bug.
Time to visit http://bugs.python.org. There are a few bugs related to c_char
and create_string_buffer
which are in the same field, but none reporting that giving it a str
now fails (but there are definite examples showing it used to work in Py3K).
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