SAS/C varargs

[girv]

One for the C gurus

How do you pass a function's variable arguments to another function ?
...also known as...
Why does the below code print garbage ?

VOID fmttest(
	STRPTR a_fmt,
	...
)
{
	va_start(ap, a_fmt);
	printf(a_fmt, ap);
	va_end(ap);
}

...

fmttest("%d %d %d\n",1,2,3);

[OddbOd]

I am no C expert (I probably know a lot less than you do) however the actual call itself looks valid. As I can't give you a complete answer without complete code here are a couple of things to check:

1) Variadic functions require prototypes, I assume you have

void fmttest( char *format, va_list arg_ptr );

before your function definitions?

2) Where is the argument pointer ap defined and initialised? By the looks of things, nowhere, it should be defined with the va_list type before being initialised by va_start().

Now I think about it a bit more your code fragment looks a lot like vprintf(), maybe a quick read through this might be useful.

[girv]

Originally Posted by OddbOd

1) Variadic functions require prototypes

I didn't know that, I'll try it. Thanks

Originally Posted by OddbOd

2) Where is the argument pointer ap defined and initialised?

Its missing from the above code, sorry.

VOID fmttest(
	STRPTR a_fmt,
	...
)
{
	va_list ap;

	va_start(ap, a_fmt);
	printf(a_fmt, ap);
	va_end(ap);
}