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Re: SCM to C string

From: Brett Viren
Subject: Re: SCM to C string
Date: Thu, 20 Jun 2002 17:04:32 -0400

Viktor Pavlenko writes:
 > Hi All,
 > I've started playing with guile recently and am very excited about
 > it:)
 > My program parses a scheme config file. If configuration is not valid
 > from the application point of view (but is a valid scheme expression)
 > I signal error. What I would like to do is to dump the offending SCM
 > object to C-style string so that I can display it as debugging
 > information.
 > For instance I'd like convert SCM object which contains '("a" 1) into
 > C string "(\"a\" 1)".

Why do you need to escape the double quotes?  If you have a null
terminated string, you should be able to print it (or pass it to a Gui
or whatever) in C just fine.  Or do I miss something.

I asked a similar question some time back, maybe the following can
help.  It turns a scheme procedure into its coresponding source code.
But, I guess it will fail to do what you want for compiled procedures
as well as arbitrary scheme forms.  The following is C++, if you are
using strict C just return the "cptr" and ignore the "string" object.

string EOS::Guile::ScmSource(SCM proc)
    static SCM result = SCM_UNDEFINED;
    if (result == SCM_UNDEFINED) {
        result = gh_eval_str("(lambda (proc) (call-with-output-string (lambda 
(p) (display (cddr (procedure-source proc)) p))))");

    SCM src = gh_call1(result,proc);
    char* cptr = gh_scm2newstr(src,0);
    cptr[strlen(cptr)-1] = '\0';
    string s(cptr+1);
    cptr[0] = '0';
    free (cptr);
    return s;


PS: looking at this old code now and relating to another recent
thread, I should probably be calling "scm_unprotect_object(result)"
after coping out the string....

Hmm, also, I'm not sure why I am truncating that last character....

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