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Path: utzoo!mnetor!seismo!think!ima!haddock!karl
From: karl@haddock
Newsgroups: net.lang.c
Subject: Re: Missing stdio features.
Message-ID: <86900044@haddock>
Date: Mon, 8-Sep-86 14:54:00 EDT
Article-I.D.: haddock.86900044
Posted: Mon Sep  8 14:54:00 1986
Date-Received: Mon, 8-Sep-86 20:51:57 EDT
References: <3438@robin.cs.nott.ac.uk>
Lines: 40
Nf-ID: #R:robin.cs.nott.ac.uk:3438:haddock:86900044:000:1545
Nf-From: haddock!karl    Sep  8 14:54:00 1986


umcp-cs!chris (Chris Torek) writes:
>In article <86900034@haddock> karl@haddock writes:
>>>>FILE *fopenfxn(int (*fxn)(), char *mode)
>>Actually, the function argument should probably be analogous to read/write
>>rather than getc/putc.  But there should be one more argument to fopenfxn(),
>>viz. a (void *) argument to be passed to fxn() to distinguish streams.
>
>Indeed, there would be a certain symmetry to the whole thing if one
>could write
>    reader(f, buf, len) FILE *f; { return (read(fileno(f), buf, len)); }
>    FILE *f = fopenrf(reader, "r");
>    fileno(f) = fd;
>instead of
>    FILE *f = fdopen(fd, "r");

As I mentioned, I think it has to be (void *) in general, thus
   reader(void *v, char *buf, int len) {
       return (read(*(int *)v, buf, len));
   }
   FILE *f = fopenrf(&fd, reader, "r");
so that the more general cases could be supported, e.g. read from string:
   typedef struct { char *t_start, *t_end; } tbuf;
   reader(void *v, char *buf, int len) {
       register tbuf *t = (tbuf *)v;
       len = min(len, t->t_end - t->t_start);
       memcpy(buf, t->t_start, len);
       t->start += len;
       return (len);
   }
   FILE *f = fopenrf(&t, reader, "r");

You could get away with having the first arg to reader() be "FILE *", but in
any case "void *_id" needs to replace or supplement the existing "int _file"
in the FILE structure.

If there are separate functions fopenrf() and fopenwf(), is there any need
for the third argument?

Karl W. Z. Heuer (ima!haddock!karl; karl@haddock.isc.com), The Walking Lint