www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - A DLL to modify a variable?

reply Gilles G. <schaouette free.fr> writes:
Hello,
maybe I am obviously missing something, but it seems that my dll doesn't modify
the value of the variables.
It looks like this:
=== File from the DLL (with the corresponding def file)
extern(Windows) void modifyThis(int* val){*val=0;}

=== call to the DLL function in the test program
alias void function(int*) modifyThis_t;
modifyThis_t modifyThis;
HMODULE h;
h = LoadLibraryA("test.dll");
int value=1;
modifyThis = cast(modifyThis_t) GetProcAddress(h,"modifyThis");
writefln("Value before call: %d",value);
(*modifyThis)(&value);
writefln("Value after call: %d",value);

But then I get the output:
Value before call: 1
Value after call: 1

I guess this is a beginner's question...
Thanks a lot!
Jun 26 2007
parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
Gilles G. wrote:

 Hello,
 maybe I am obviously missing something, but it seems that my dll doesn't
modify the value of the variables.
 It looks like this:
 === File from the DLL (with the corresponding def file)
 extern(Windows) void modifyThis(int* val){*val=0;}
 
 === call to the DLL function in the test program
 alias void function(int*) modifyThis_t;



I *could* be wrong, but this looks to be incorrect.  It should be (if I
remember correctly):

extern(Windows)
{
    alias void function(int*) modifyThis_t;
}

Otherwise, the function type will use the D calling convention, which is
probably incompatible with stdcall.

Give it a shot, anyway.

	-- Daniel
Jun 26 2007
parent reply Gilles G. <schaouette free.fr> writes:
Thanks a lot, I would never find this one.

--
Gilles

Daniel Keep Wrote:


 
 
 Gilles G. wrote:

 Hello,
 maybe I am obviously missing something, but it seems that my dll doesn't
modify the value of the variables.
 It looks like this:
 === File from the DLL (with the corresponding def file)
 extern(Windows) void modifyThis(int* val){*val=0;}
 
 === call to the DLL function in the test program
 alias void function(int*) modifyThis_t;



 I *could* be wrong, but this looks to be incorrect.  It should be (if I
 remember correctly):
 
 extern(Windows)
 {
     alias void function(int*) modifyThis_t;
 }
 
 Otherwise, the function type will use the D calling convention, which is
 probably incompatible with stdcall.
 
 Give it a shot, anyway.
 
 	-- Daniel
Jun 26 2007
parent Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:
Gilles G. wrote:

 Thanks a lot, I would never find this one.
 
 --
 Gilles



Additionally, you don't have to explicitly dereference the function
pointer.  Just calling 'modifyThis(&value)' will suffice.  Not part of 
your problem, but I thought it worth mentioning for readability sake.

-- Chris Nicholson-Sauls
Jun 26 2007