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[REBOL] Re: Problems with accessing external lib in /Command

From: jeff:rebol at: 6-Mar-2001 7:52

Howdy, Coussement:
> Hi fellow Rebolians: > > Because I need to use the user name in an NT-networking env, I thought to > use the "GetUserNameA" function from from ADVAPI32.dll ... > > Based on the code found on MSDN at > , I tried:
Always base your routines off the C version of these functions, rather than the Visual Basic function that the above describes. The addressing mode of the different parameters isn't immediately clear when looking at the VB declaration. So we open MSVC and find: BOOL GetUserName( LPTSTR lpBuffer, // address of name buffer LPDWORD nSize // address of size of name buffer ); (ie, to decode the "Hungarian notation" above: long pointer to string == char* and long pointer to DWORD == int* ) Okay, now this is probably one of the most important tricks with REBOL/Command which is undocumented, though if you're a C programmer, it should be fairly intuitive. This really needs to be published into an addendum, probably, so here it goes: In C, a pointer to a struct is a pointer to the struct's first element. In REBOL/Commands, all structs are passed by reference. What's this mean? This means struct! values in REBOL/Command allow you to make references to values, for example, we need this int*. REBOL/Command doesn't directly provide support for pointer to int, but it's easy to make it using a struct! value to wrap our integer, for example: advapi32: load/library %advapi32.dll get-user-name: make routine! [ name [string!] l-ref [struct! [len [integer!]]] return: [integer!] ] advapi32 "GetUserNameA" insert/dup name: copy "" " " 255 ;-pad the buffer l-ref: make struct! [len [integer!]] [255] get-user-name name l-ref trim name == "jeff"