Python bindings and large std::string value produces char * swig object
<[email protected]> Mon, 27 Jan 2025 13:06:58 -0800
| Newsgroups | gmane.comp.programming.swig |
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Dear Swig Community,
I am using swig 4.3.0 and Python 3.9.5 on an x64 Windows 11 platform. I
have a third-party Python database module compiled with Visual Studio C++
2017 that uses swig bindings, originally designed for Python 2. One class
that we are using has a method that returns strings to Python. For example:
> str_val = v.asString() # v is an instance of the class in question
If v is the swig object, str_val = v.asString() should store the string to
variable str_val.
Most of the time this works flawlessly. However, for very large results,
str_val does not receive the value of the string, but rather another swig
proxy object for a pointer to a character string:
> str_val = v.asString()
> str_val
<Swig Object of type 'char *' at 0x000001951F1F5990>
The underlying C++ library declares the method as returning std::string and
we have included std_string.i in our interface. I did modify some of the
other templates in the library to use the Python library Unicode interface,
but I do not think that this should be relevant for a std::string return.
An unsolved 2018 post on stackoverflow reported what seems to report the
same issue
(https://stackoverflow.com/questions/50056859/c-string-to-python-limitation-
using-swig, they note the error at strings longer than 2 GB which is
probably my case), does anyone have suggestions? I also saw this behavior
with swig 4.1.1.
Thank you,
Marie
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class=3DWordSection1><p class=3DMsoNormal><o:p> </o:p></p><p =
class=3DMsoNormal>Dear Swig Community,<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>I am using =
swig 4.3.0 and Python 3.9.5 on an x64 Windows 11 platform. I have =
a third-party Python database module compiled with Visual Studio C++ =
2017 that uses swig bindings, originally designed for Python 2. =
One class that we are using has a method that returns strings to =
Python. For example:<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>> str_val =
=3D v.asString() # v is an instance of the class in question =
<o:p></o:p></p><p class=3DMsoNormal><o:p> </o:p></p><p =
class=3DMsoNormal>If v is the swig object, str_val =3D v.asString() =
should store the string to variable str_val.<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>Most of the =
time this works flawlessly. However, for very large results, =
str_val does not receive the value of the string, but rather another =
swig proxy object for a pointer to a character string:<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>> str_val =
=3D v.asString()<o:p></o:p></p><p class=3DMsoNormal>> =
str_val<o:p></o:p></p><p class=3DMsoNormal> <Swig =
Object of type 'char *' at 0x000001951F1F5990><o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>The =
underlying C++ library declares the method as returning std::string and =
we have included std_string.i in our interface. I did modify some =
of the other templates in the library to use the Python library Unicode =
interface, but I do not think that this should be relevant for a =
std::string return. <o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>An unsolved =
2018 post on stackoverflow reported what seems to report the same issue =
(https://stackoverflow.com/questions/50056859/c-string-to-python-limitati=
on-using-swig, they note the error at strings longer than 2 GB which is =
probably my case), does anyone have suggestions? I also saw this =
behavior with swig 4.1.1.<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p class=3DMsoNormal>Thank =
you,<o:p></o:p></p><p class=3DMsoNormal>Marie<o:p></o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p><p =
class=3DMsoNormal><o:p> </o:p></p></div></body></html>
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