Multiple Arguements like in printf

[bg_ie]

Hi,

I'd like to write a function like printf, which takes a string as its
first arguement, but then a variable number of arguements after this,
based on the contents of the first arguement.

How do I do this?

Barry.

[Michael Mair]

bg***@yahoo.com schrieb:

I'd like to write a function like printf, which takes a string as its
first arguement, but then a variable number of arguements after this,
based on the contents of the first arguement.

How do I do this?

http://c-faq.com/varargs/index.html
Start from 15.4 and read a little bit further.

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

[Malcolm]

<bg***@yahoo.co m> wrote in message

Hi,

I'd like to write a function like printf, which takes a string as its
first arguement, but then a variable number of arguements after this,
based on the contents of the first arguement.

The easy, cheating way.

int myprintf(char *fmt, ...)
{
va_list args;
char buff[2048];
int answer;

va_start(args, fmt);
answer = vsprintf(buff, fmt, args);
puts(buff);
va_end(args);
return answer;
}

The real answer

int myprintf(char *fmt, ...)
{
va_list args;
int answer;
int aninteger;
double areal;

va_start(&fmt, args);
while(*fmt)
{
if(*fmt == '%'))
{
fmt++;
if(*fmt == 'd')
{
aninteger = va_arg(args, integer);
printinteger(an integer);
}
else if(fmt == 'f')
{
areal = va-arg(args, double);
printreal(areal );
}
fmt++;
}
else
{
putc(*fmt);
fmt++;
}
}

va_end(args);
return answer;
}

This is a very cut down printf() since it only handles %d and %f, and I
haven't included the subroutines for converting between numbers and strings.
You can see how with substantial effort you can expand it to include all of
the printf() format specifiers, field widths, and so on.

[Keith Thompson]

"Malcolm" <re*******@btin ternet.com> writes:

<bg***@yahoo.co m> wrote in message

I'd like to write a function like printf, which takes a string as its
first arguement, but then a variable number of arguements after this,
based on the contents of the first arguement.
The easy, cheating way.

int myprintf(char *fmt, ...)
{
va_list args;
char buff[2048];
int answer;

va_start(args, fmt);
answer = vsprintf(buff, fmt, args);
puts(buff);
va_end(args);
return answer;
}

The real answer

int myprintf(char *fmt, ...)
{
va_list args;
int answer;
int aninteger;
double areal;

va_start(&fmt, args);
while(*fmt)
{
if(*fmt == '%'))

[snip] va_end(args);
return answer;
}

This is a very cut down printf() since it only handles %d and %f, and I
haven't included the subroutines for converting between numbers and strings.
You can see how with substantial effort you can expand it to include all of
the printf() format specifiers, field widths, and so on.

Using vsprintf() is relatively easy, but it's not cheating in any
reasonable sense of the term, assuming it's appropriate to your needs.
If vsprintf() does the job, it would be unreasonable *not* to use it.
(If it doesn't, of course, then you'll have to roll your own solution.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Chris Torek]

In article <L4************ *************** ***@bt.com>
Malcolm <re*******@btin ternet.com> wrote:

[snippage, with the aim to keep just the va_start() lines plus enough
context for them to make sense]

int myprintf(char *fmt, ...) {
va_list args;
va_start(args, fmt); [and]int myprintf(char *fmt, ...) {
va_list args;
va_start(&fmt, args);

"Two men claim they're Jesus
One of them must be wrong..." --Mark Knopfler

(At least one of the two va_start()s above must be wrong. In fact,
the first one is correct and the second is wrong.)
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) [phone]
email: forget about it http://web.torek.net/torek/index.html
Reading email is like searching for food in the garbage, thanks to spammers.

[Malcolm]

"Chris Torek" <no****@torek.n et> wrote

In article <L4************ *************** ***@bt.com>
Malcolm <re*******@btin ternet.com> wrote:

[snippage, with the aim to keep just the va_start() lines plus enough
context for them to make sense]

int myprintf(char *fmt, ...) {
va_list args;
va_start(args, fmt);

[and]

int myprintf(char *fmt, ...) {
va_list args;
va_start(&fmt, args);

"Two men claim they're Jesus
One of them must be wrong..." --Mark Knopfler

(At least one of the two va_start()s above must be wrong. In fact,
the first one is correct and the second is wrong.)

You're right.
Sorry.
It's ages since I wrote a variadic function.
--
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