Re: Java char *INOUT doesn't OUT

Gary Nissen wrote:

> Hi,
>
> I'm using SWIG-1.3.22 on Windows with Java JDK 1.4.2.
>
> I'm trying to wrap a C DLL.  All parameters are passed as pointers (int *, 
> double *, and char *).  Most parameters are *INPUT, but some are *INOUT.  The 
> int *INOUT and double *INOUT work as expected by turning the parameter into a 
> single dimensional array.  But a char *INOUT turns the parameter into a String, 
> basically making it a char *INPUT.
>
> I expected the char *INOUT to allow me to pass Strings back and forth via a 
> 1-dimensional array just like int *INOUT.  Am I off track?  Is there a better 
> method to do this?
>
> Through my struggles I also tried the *SBUF and *BYTE methods.  Unfortunately neither worked for me.  
>
> The *SBUF caused Access Violations because the char array was a different 
> length than the string contained in the StringBuffer.  It was using the 
> capacity of a StringBuffer instead of the length of the String contained in it. 
>  I tried changing the typemap to use length.  Then I received Access Violations 
> when the resulting string was being appended back to the StringBuffer.  I 
> wasn't able to figure out why that was failing.
>
> The *BYTE caused garbage to be pasted back into my String.  I was using the 
> BYTE method this way:
>
> String s = "0123456789";
> byte[] b = s.toByteArray();
> int r = DLLWrapper.getResult(b);
> s = new String(b);
>
> System.out.println(s);
>
> This resulted in garbage printouts.
>
> Any advice on the best/easiest way to do this?  

SWIG wraps char* as a string, that is well documented. To change the behaviour 
of char* to a pointer to an in/out single char character, apply the 'signed char 
*' typemaps.

%include "typemaps.i"
%apply signed char *INOUT {char *pnum};
%typemap(freearg) char *pnum "";

void foo(char *pnum);

Unfortunately the default char* typemaps require a freearg typemap and this is 
still picked up, thus the extra typemap above to clear the freearg typemap. I'll 
change this so it won't be necessary in the future.

William
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