swig question
bill...@alum.mit.edu
returns a dynamically allocated string
which is assigned to "result" below. Swig returns this in Tcl as
follows:
Tcl_SetObjResult(interp,Tcl_NewStringObj(result,-1));
As I understand it, this creates a new copy of the string as part of
the newly created Tcl object. While Tcl's memory management handles the
copy, the string created by my C function will not be garbage collected
by Tcl, so as it stands, this is a memory leak.
Things seem to work just fine if I add to the code generated by swig:
free((void *) result);
after the call to TclSetObjResult.
My questions are:
(a) have I misunderstood anything here?
(b) is there a way to get swig to free the C string so that I don't
have to do it by editing the output of swig?
(c) if I distribute my edited version of the wrapper file generated by
swig, will it be portable? That is, is the code generated by swig
system-dependent? I can't find anything in the swig documentation about
this.
Georgios Petasis
better to post your function part that the string is returned, its
prototype and the whole wrapper function generated by swig :-)
George
Robert Heller
>
> I am using swig to provide a Tcl interface to a C library. One function
> returns a dynamically allocated string
> which is assigned to "result" below. Swig returns this in Tcl as
> follows:
>
>
> Tcl_SetObjResult(interp,Tcl_NewStringObj(result,-1));
>
>
> As I understand it, this creates a new copy of the string as part of
> the newly created Tcl object. While Tcl's memory management handles the
> copy, the string created by my C function will not be garbage collected
> by Tcl, so as it stands, this is a memory leak.
>
> Things seem to work just fine if I add to the code generated by swig:
>
>
> free((void *) result);
>
>
> after the call to TclSetObjResult.
>
>
> My questions are:
>
> (a) have I misunderstood anything here?
No.
>
> (b) is there a way to get swig to free the C string so that I don't
> have to do it by editing the output of swig?
>
Yes. You need to write a typemap for this case. This will allow you to
include some special handling.
> (c) if I distribute my edited version of the wrapper file generated by
> swig, will it be portable? That is, is the code generated by swig
> system-dependent? I can't find anything in the swig documentation about
> this.
The code generated by swig is cross-platform. Any code you insert
(manually or via a typemap) might or might not be. If you are using
autoconf and/or TEA you should make sure all the generated -D<mumble>
flags are passed to your swig call (in your Makefile.in) and then you
can test them with #ifdef's (in the typemap code) to be sure you
generate portable code. Presumbably, your C library is doing this, in
terms of it calling the proper flavor of malloc()/calloc(), etc. and
you can use these flags to call the matching flavor of free().
>
>
--
Robert Heller -- 978-544-6933
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http://www.deepsoft.com/ -- Web Hosting, with CGI and Database
hel...@deepsoft.com -- Contract Programming: C/C++, Tcl/Tk
bill...@alum.mit.edu
function returns a dynamically allocated string which is assigned to
"result" below. Swig returns this in Tcl as follows:
Tcl_SetObjResult(interp,Tcl_NewStringObj(result,-1));
As I understand it, this creates a new copy of the string as part of
the newly created Tcl object. While Tcl's memory management handles the
copy, the string created by my C function will not be garbage collected
by Tcl, so as it stands, this is a memory leak: every call to the Tcl
function will cause my C function to allocate a new string that will
not be garbage collected by Tcl.
Things seem to work just fine if I add to the code generated
by swig:
free((void *) result);
after the call to TclSetObjResult.
My questions are:
(a) have I misunderstood anything here?
(b) is there a way to get swig to free the C string so that I don't
have to do it by editing the output of swig?
(c) if I distribute my edited version of the wrapper file generated by
swig, will it be portable? That is, is the code generated by swig
system-dependent? Or must I write a script to insert the free()into the
code generated by swig?
pal...@yahoo.com
For example, something along the following lines
%{
typedef char * malloced_str;
%}
%typemap(out) malloced_str %{
if ($1 == NULL) {
/* Assumes NULL return is a failure */
Tcl_SetResult(interp, ........);
SWIG_fail;
}
else {
Tcl_SetObjResult(interp, Tcl_NewStringObj($1, -1));
}
%}
%typemap(ret) malloced_str "if ($1) free($1);"
malloced_str my_function();
Note this assumes the function returns the string as a return value. If
it is passed out through a parameter poiunter, you will need a
typemap(argout) that does something similar
/Ashok
bill...@alum.mit.edu
particular problem, which I eventually found in the Swig manual while
studying typemaps. In my .i file I include the declaration:
%newobject UNStrToWNStr;
That tells Swig that the function returns newly allocated memory and
induces it to add a free by itself in the _wrap.c file.
Incidentally, the reason I posted twice is that the first one didn't
appear for a very long time, over an hour, so I mistakenly concluded
that something had gone wrong. After it appeared, I was unable to
respond to posts in this thread. Every time I clicked on the "Reply"
button I got an error message. Anyone know what was wrong?
Bill