variadic function calling variadic function

[gold...@signalsguru.net]

I'm not sure if I'm doing something stupid, or if I'm not understanding
how to use variadic functions. These functions appear to be working
individually. In ast_call, I can vprintf the argument list and it
looks fine. If I invoke write_cmd, it seems to work fine. But when I
invoke write_cmd in ast_call with argp, I get garbage in argp in
write_cmd. I don't know where it's breaking.

int ast_call(struct ast_connection *conn, char *msg, ...)
{
va_list argp;

va_start(argp,msg);
if(!write_cmd(conn->socket,msg,argp)) {
va_end(argp);
return write_FAIL;
}
va_end(argp);
if(!conn->params.wait_for_resp)
return AST_SUCCESS;
return ast_wait_peek_by_id(conn,conn->cnt++);
}

static int write_cmd(int socket, char *msg, ...)
{
int n=0,len=0,slen;
va_list argp;
char buf[BUFSIZE];

va_start(argp,msg);
vsprintf(buf,msg,argp);
va_end(argp);
slen = strlen(buf);
puts(buf);
for(len=0; len<slen;) {
if((n = write(socket,buf+len,slen-len)) < 0)
return 0;
len += n;
}
return 1;
}

[Michael Mair]

gold...@signalsguru.net schrieb:

http://c-faq.com/varargs/ , especially 15.5 and 15.6

-Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

[gold...@signalsguru.net]

Michael Mair wrote:
<snip>

>
> http://c-faq.com/varargs/ , especially 15.5 and 15.6
>
> -Michael
> --
> E-Mail: Mine is an /at/ gmx /dot/ de address.

Isn't that what I'm doing? I don't understand what 15.6 has to do with
my problem. I called

va_start(argp,msg);
vsprintf(buf,msg,argp);
va_end(argp);

and

va_start(argp,msg);
if(!write_cmd(conn->socket,msg,argp)) {
va_end(argp);
return write_FAIL;
}
va_end(argp);

I'm just not seeing it. It must be obvious to someone. Thanks.

[Chris Torek]

In article <1146635643.3...@j73g2000cwa.googlegroups.com>

<gold...@signalsguru.net> wrote:
>I'm not sure if I'm doing something stupid, or if I'm not understanding
>how to use variadic functions.

Michael Mair already pointed you at the FAQ entry. I will add
a few more remarks here:

>... In ast_call, I can vprintf the argument list and it
>looks fine.

Note, you are calling vprintf(), not printf(), when it "works fine".

>If I invoke write_cmd [directly], it seems to work fine.

Here you are calling printf-- er, I mean write_cmd(), not vprintf--
oops, I mean vwrite_cmd().

>But when I invoke write_cmd in ast_call ...

You need to call vwrite_cmd().

Of course, you first need to *write* vwrite_cmd(). This is easy
since you already have all the appropriate code:

>static int write_cmd(int socket, char *msg, ...)
>{
> int n=0,len=0,slen;
> va_list argp;
> char buf[BUFSIZE];
>
> va_start(argp,msg);
> vsprintf(buf,msg,argp);
> va_end(argp);
> slen = strlen(buf);
> puts(buf);
> for(len=0; len<slen;) {
> if((n = write(socket,buf+len,slen-len)) < 0)
> return 0;
> len += n;
> }
> return 1;
>}

Change the ", ..." part to take a "va_list" argument, stop calling
va_start and va_end (since you already have the va_list), and leave
the rest of the code as-is. Then rewrite write_cmd() in terms of
a call to vwrite_cmd() (to eliminate redundancy and thus improve
maintainability, and incidentally save code space too).
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603
email: forget about it http://web.torek.net/torek/index.html
Reading email is like searching for food in the garbage, thanks to spammers.

[Flash Gordon]

Michael did not point you at the most appropriate question, which is 15.12

He possibly expected you to work it out from how vsprintf works.
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
comp.lang.c posting guidelines and intro:
http://clc-wiki.net/wiki/Intro_to_clc

[gold...@gmail.com]

For some reason the vprintf/printf thing wasn't clicking. The last two
posts put me on the right track. Thanks.