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[REBOL] Re: How to send big string to library and back?

From: jeff:rebol at: 16-Apr-2001 7:44

Howdy, Petr:
> But my friend asked me a question I am not able to answer > him. According to him, in C language, string is ended by > "0" char. So if my image data will contain "0" char, it > could be regarded as an end of a tring by internal Rebol > library interface routines.
First, let me clarify the terminology: In REBOL: In shared library: ------------------------------------------ routine! "external library routine" In REBOL you may have string data that contains null characters. REBOL doesn't care. In C, operations that work on a string consider the null character as a terminator. If you are working with an external library routine that expects image data, then that routine most likely does not consider null characters as the end of data. So you can happily pass along string! to any external library routine that is expecting a pointer to any kind of data. The only hitch is having that memory come back. The way COMMAND works now is that if you have a return type of string! (or char*) then REBOL/Command must find the null terminator-- otherwise you have some unbounded string hanging out (which can't happen). If you have a data buffer going off to a shared library from command that you would like to operate on both in REBOL and in the external routine, I recommend: 1. doing all your manipulations on that data from REBOL first. 2. returning an integer! instead of a string! which allows you to hold the pointer to that memory but does not provide it. 3. Pass a reference (address of) to your buffer to an external routine which will modify it "in place". For example: // FOR UNIX -- REBOL [ Needs: [Command] ] write %zap-buff.c reform ["#include <string.h>" newline "void zap_buff(char ** buf, char what, int len) {memset(*buf, what, len);}" ] call/wait "gcc -fPIC -shared zap-buff.c -o" zbl: load/library zap-buff: make routine! [ b-wrap [struct! [buf [string!]]] what [char] len [int] ] zbl "zap_buff" buff: {foo bar baz ^@ ^@ bing} b-wrap: make struct! [buf [string!]] reduce [buff] foreach c "REBOL^@" [ zap-buff b-wrap c length? buff ?? buff ] The memory inside our BUFF in REBOL is actually manipulated by the external library. Scary cool stuff.. :-) -jeff