Having trouble using CTypes with a custom function

[tkondal@gmail.com]

Hi all.

I just started looking at Python's ctypes lib and I am having trouble
using it for a function.

For starters, here's my Python code:


from ctypes import*;
myStringDLL= cdll.LoadLibrar y("myStringDLL. dll");

GetMyString = getattr(myStrin gDLL,
"?GetMyString@@ YA_NAAV?$basic_ string@DU?$char _traits@D@std@@ V?$allocator@D@ 2@@std@@@Z")

strString = create_string_b uffer('\000' * 256);
GetMyString.res type = c_int;
GetMyString.arg types = [c_char_p];

bResult = GetMyString (strSerialNumbe r);

print (bResult);
print (strSerialNumbe r);

#C++ Prototype of the function I want to call:
#bool GetMyString (string& stringParam) ;




I do not have access to the source code of this function so don't ask
me to try different things in C++. This DLL is working fine.

The problem that I have is that print (strSerialNumbe r) does not seem
to print the correct string. What I get is some garbage value of
unprintable characters. Am I using this the correct way?

Thanks.

[Chris Mellon]

Re: Having trouble using CTypes with a custom function

On 4 Oct 2006 11:18:16 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:

Hi all.
>
I just started looking at Python's ctypes lib and I am having trouble
using it for a function.
>
For starters, here's my Python code:
>
>
from ctypes import*;
myStringDLL= cdll.LoadLibrar y("myStringDLL. dll");
>
GetMyString = getattr(myStrin gDLL,
"?GetMyString@@ YA_NAAV?$basic_ string@DU?$char _traits@D@std@@ V?$allocator@D@ 2@@std@@@Z")
>
strString = create_string_b uffer('\000' * 256);
GetMyString.res type = c_int;
GetMyString.arg types = [c_char_p];
>
bResult = GetMyString (strSerialNumbe r);
>
print (bResult);
print (strSerialNumbe r);
>
#C++ Prototype of the function I want to call:
#bool GetMyString (string& stringParam) ;
>
>
>
>
I do not have access to the source code of this function so don't ask
me to try different things in C++. This DLL is working fine.
>
The problem that I have is that print (strSerialNumbe r) does not seem
to print the correct string. What I get is some garbage value of
unprintable characters. Am I using this the correct way?
>

This function is expecting a C++ std::string object, not a regular C
style string. You'll need a wrapper function, and one which uses the
same compiler and STL as the C++ source.

Thanks.
>
--

http://mail.python.org/mailman/listinfo/python-list

>

[tkondal@gmail.com]

Re: Having trouble using CTypes with a custom function

Would you have any example of a wrapper for such data types?

Thanks.

Chris Mellon wrote:

On 4 Oct 2006 11:18:16 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:

Hi all.

I just started looking at Python's ctypes lib and I am having trouble
using it for a function.

For starters, here's my Python code:


from ctypes import*;
myStringDLL= cdll.LoadLibrar y("myStringDLL. dll");

GetMyString = getattr(myStrin gDLL,
"?GetMyString@@ YA_NAAV?$basic_ string@DU?$char _traits@D@std@@ V?$allocator@D@ 2@@std@@@Z")

strString = create_string_b uffer('\000' * 256);
GetMyString.res type = c_int;
GetMyString.arg types = [c_char_p];

bResult = GetMyString (strSerialNumbe r);

print (bResult);
print (strSerialNumbe r);

#C++ Prototype of the function I want to call:
#bool GetMyString (string& stringParam) ;




I do not have access to the source code of this function so don't ask
me to try different things in C++. This DLL is working fine.

The problem that I have is that print (strSerialNumbe r) does not seem
to print the correct string. What I get is some garbage value of
unprintable characters. Am I using this the correct way?

>
>
>
>
This function is expecting a C++ std::string object, not a regular C
style string. You'll need a wrapper function, and one which uses the
same compiler and STL as the C++ source.
>

Thanks.

--

http://mail.python.org/mailman/listinfo/python-list

[Chris Mellon]

Re: Having trouble using CTypes with a custom function

<please don't top post>

On 4 Oct 2006 11:35:11 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:

Would you have any example of a wrapper for such data types?
>
Thanks.
>
Chris Mellon wrote:

On 4 Oct 2006 11:18:16 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:

Hi all.
>
I just started looking at Python's ctypes lib and I am having trouble
using it for a function.
>
For starters, here's my Python code:
>
>
from ctypes import*;
myStringDLL= cdll.LoadLibrar y("myStringDLL. dll");
>
GetMyString = getattr(myStrin gDLL,
"?GetMyString@@ YA_NAAV?$basic_ string@DU?$char _traits@D@std@@ V?$allocator@D@ 2@@std@@@Z")
>
strString = create_string_b uffer('\000' * 256);
GetMyString.res type = c_int;
GetMyString.arg types = [c_char_p];
>
bResult = GetMyString (strSerialNumbe r);
>
print (bResult);
print (strSerialNumbe r);
>
#C++ Prototype of the function I want to call:
#bool GetMyString (string& stringParam) ;
>
>
>
>
I do not have access to the source code of this function so don't ask
me to try different things in C++. This DLL is working fine.
>
The problem that I have is that print (strSerialNumbe r) does not seem
to print the correct string. What I get is some garbage value of
unprintable characters. Am I using this the correct way?
>

This function is expecting a C++ std::string object, not a regular C
style string. You'll need a wrapper function, and one which uses the
same compiler and STL as the C++ source.

Thanks.
>
--

http://mail.python.org/mailman/listinfo/python-list

>

>

in this case it'd be very simple:

bool WrapGetMyString (char * c) {
return GetMyString(c)
}


(Note: This isn't unicode safe).

The C++ compiler will handle converting from the char * to the std::string.

--

http://mail.python.org/mailman/listinfo/python-list

>

[tkondal@gmail.com]

Re: Having trouble using CTypes with a custom function

Hi Chris.

I know that it is easy to fix the problem using C++. However, I do not
want to code a wrapper DLL. I was wondering if there was a workaround
with Python. Everything has to be done in Python as we do not have the
tools for C++ (and we are not planning on getting any).

Thanks.

Chris Mellon wrote:

<please don't top post>
>
On 4 Oct 2006 11:35:11 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:

Would you have any example of a wrapper for such data types?

Thanks.

Chris Mellon wrote:

On 4 Oct 2006 11:18:16 -0700, tkondal@gmail.c om <tkondal@gmail. comwrote:
Hi all.

I just started looking at Python's ctypes lib and I am having trouble
using it for a function.

For starters, here's my Python code:


from ctypes import*;
myStringDLL= cdll.LoadLibrar y("myStringDLL. dll");

GetMyString = getattr(myStrin gDLL,
"?GetMyString@@ YA_NAAV?$basic_ string@DU?$char _traits@D@std@@ V?$allocator@D@ 2@@std@@@Z")

strString = create_string_b uffer('\000' * 256);
GetMyString.res type = c_int;
GetMyString.arg types = [c_char_p];

bResult = GetMyString (strSerialNumbe r);

print (bResult);
print (strSerialNumbe r);

#C++ Prototype of the function I want to call:
#bool GetMyString (string& stringParam) ;




I do not have access to the source code of this function so don't ask
me to try different things in C++. This DLL is working fine.

The problem that I have is that print (strSerialNumbe r) does not seem
to print the correct string. What I get is some garbage value of
unprintable characters. Am I using this the correct way?

>
>
>
>
This function is expecting a C++ std::string object, not a regular C
style string. You'll need a wrapper function, and one which uses the
same compiler and STL as the C++ source.
>
Thanks.

--

http://mail.python.org/mailman/listinfo/python-list

>
in this case it'd be very simple:
>
bool WrapGetMyString (char * c) {
return GetMyString(c)
}
>
>
(Note: This isn't unicode safe).
>
The C++ compiler will handle converting from the char * to the std::string.
>
>
>
>
>

--

http://mail.python.org/mailman/listinfo/python-list

[sjdevnull@yahoo.com]

Re: Having trouble using CTypes with a custom function

tkondal@gmail.c om wrote:

Hi all.
>
I just started looking at Python's ctypes lib and I am having trouble
using it for a function.

[...]

#C++ Prototype of the function I want to call:

ctypes provides support for calling functions in C libraries, using C
datatypes. I don't see any reason to believe it would work with other
languages (e.g. C++).