On 1 January 2013 07:43, S Krish <[email protected]> wrote:
> I am trying to work with memory addresses back n forth..
>
> Simple case of char* buffer that needs to be filled in by dll . Buffer does
> not change in Pharo after the call. Am I missing something here..
>
> The memory address that is printed out does not match what I see in Pharo /
> infact the address does not change at all... for repeated call invoked from
> debugger.
>
> C Code:
>
> DLLEXPORT int readAndWritePipe(char* outBuf )
> {
> system("Echo readAndWritePipe" );
> debugPrintf ( "readAndWritePipe: %d \n" , &outBuf , 1046 );
> memcpy ( outBuf , "Testing123\0" , 11) ;
> return 0;
> }
>
are you sure you want to print an address of argument (&outBuf)
instead of argument value (outBuf - which is a pointer value passed to
function) ?
Because &outBuf, will always be a location on stack where the value stored.
And sure thing, when you call that function from simple short test
app, it will be always same, since nothing interferes with stack.
> void debugPrintf ( char* logString, int intArg , char* strArg, int size )
> { // can redirect as needed to logger end point..
> FILE * logFile = fopen( "c:\\temp\\writePipes.log" , "a" );
> char* buf = (char*) calloc( sizeof(char) , size );
> sprintf( buf, logString , intArg , strArg );
> fputs(buf , logFile );
> fclose(logFile);
> }
>
> Pharo:
>
> testPharoBuffer: buf
>
> <primitive: #primitiveNativeCall module: #NativeBoostPlugin error:
> errorCode >
> ^ self nbCall: #( int readAndWritePipe( String buf ) ) module:
> 'TestPharo.dll'
>
>
> testPharoBuffer
> "self new testPharoBuffer "
> | buf addr addr2 |
> buf := String new: 100000.
> addr := buf asNBExternalString.
> addr2 := ( NativeBoost allocate: 256 ).
> self testPharoBuffer: addr . " or use addr2, both of it does not
> work"
> Transcript cr; show: buf.
>
String type in signature makes a copy of string on stack + adds
null-terminating character, and then pushing the pointer on stack as
argument to function.
So, it is more like 'pass by value-copy' argument.
If you want to do 'pass by reference', just use 'void *' (or char* )
in function signature, but then make sure you null-terminate stuff
there by yourself, if needed.
String type converter is more for convenience to avoid dealing with
null-terminating chars every time.
But sure thing, if you need to pass a pointer to buffer, where
function will store something ,you should not use it.
--
Best regards,
Igor Stasenko.
