Jiminion Jiminion - 6 months ago 52
Python Question

SWIG/Python: Passing pointer into function

I basically want to do exactly this:

swig: how to pass void* into generic function

I seem to be able to get a value that Python can hold, but when I pass it back in, it is deemed null and causes a fail. So I'm thinking I need some kind of PyObject conversion. I don't know why void pointers should be so hard to handle.

(I'm actually working with HMODULE, but I think if I can get void pointers to work, I can get them to work as well.

Basically, I just want to:

>>hmod = example.load_module("fooModName")
>>example.run_module(hmod, par1, par2)


How do I define the input and output typemaps such that these two calls can be supported?

I am trying to work with HMODULE (defined in Windows.h , eventually as a void pointer)

HMODULE load_library(char *pathDLL);
int get_api(HMODULE dll); // loads/updates api


===========================================================

I have figured out my actual problem.

My routines when wrapped would be:

>>ModuleName = example.find_module_name("lookDir")
>>HModule = example.load_module(ModuleName)


The problem is that the returned name is a char string (char *) but the LoadLibrary() MSDN routine needs a LPCWSTR. I can readily convert the string within the routine, but that breaks it for other use, so I'd really like to convert the string within an input wrapper.

I think the solution is a typemap of some sort.

I am trying this:

%typemap(in) char* inpathDLL {
static wchar_t LpathDLL[2048];
MultiByteToWideChar(CP_ACP, 0, $input, -1, LpathDLL, 2048);
$1 = LpathDLL;
}


This is failing. It seems to thing the input is a python string object, so I somehow have to get it to convert it to a char * before applying the next conversion.

How do I get this input string converted?

ANSWER:

OK, I found a (the?) fix. The trick is to use 'check' which adds code after the default conversion:

%typemap(check)char* inpathDLL {
if ($1 != NULL) {
static wchar_t LpathDLL[2048];
MultiByteToWideChar(CP_ACP, 0, $1, -1, LpathDLL, 2048);
$1 = (char *)LpathDLL;
}
}

Answer

Swig supports that usage directly, with no typemaps required.

One way to get your code snippet to work is as follows:

/* File : example.c */

void *
load_module(const char* name)
{
    static int module_handle = 12;
    printf("Hoory, loaded %s\n", name);
    return &module_handle;
}
void
example_run_module(void* handle, int par1, int par2)
{
    printf("Yay! Running module %d: %d %d\n",
        *(int*)handle, par1, par2);
}

 

/* example.i */
%module example
%{
void * load_module(const char* name);
void example_run_module(void* handle, int par1, int par2);
%}  

void * load_module(const char* name);
void example_run_module(void* handle, int par1, int par2);

 

# SConscript
Import('env')
env.Replace(SWIGFLAGS=['-python'])
env.ParseConfig('/usr/bin/python-config --cflags --ldflags')
lib = env.SharedLibrary('_example.so', ['example.c', 'example.i'])
env.Clean(lib, 'example.pyc')

Result:

In [5]: import example

In [6]: example.load_module("hayhay")
Hoory, loaded hayhay
Out[6]: <Swig Object of type 'void *' at 0x7f18cca05180>

In [7]: import example

In [8]: x=example.load_module("hayhay")
Hoory, loaded hayhay

In [9]: example.example_run_module(x, 3, 4)
Yay! Running module 12: 3 4
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