Passing va_list two times?

[Andrej Prsa]

Hi!

If I declare two functions like this:

int execute_command (char *name, ...)
{
va_list args;

va_start (args, name);
my_func (1, args);
va_end (args);
}

int my_func (int argc, ...)
{
va_list args;
char *str;

va_start (args, argc);
str = va_arg (args, char *);
printf ("%s\n", str);
va_end (args);
}

and call them from e.g.

execute_command ("my_command", "my argument");

parsing of args is OK at the first function (e.g. if I cut & paste the
va_arg and printf part to the first function), but garbage is printed in
the second function. I'm surely missing something obvious, but I can't see
it. Help?

Thanks,

Andrej

 

[Mike Wahler]

Hi!

If I declare two functions like this:

int execute_command (char *name, ...)
{
va_list args;

va_start (args, name);
my_func (1, args);
va_end (args);
}

int my_func (int argc, ...)
{
va_list args;
char *str;

va_start (args, argc);
str = va_arg (args, char *);
printf ("%s\n", str);
va_end (args);
}

and call them from e.g.

execute_command ("my_command", "my argument");

parsing of args is OK at the first function (e.g. if I cut & paste the
va_arg and printf part to the first function), but garbage is printed in
the second function. I'm surely missing something obvious, but I can't see
it.

Um, 'char*' and 'int' are different types?
(taking literally your remark about cut/paste)

int i;

/* ... */

i = va_arg(args, int);

cut/copy/paste is a double-edged sword.

-Mike

 

[those who know me have no need of my name]

in comp.lang.c i read:

int execute_command (char *name, ...)
{
va_list args;

va_start (args, name);
my_func (1, args);
va_end (args);
}

int my_func (int argc, ...)

args is a va_list, not a ..., so you cannot do this. make my_func's second
argument a va_list, drop the va_start and va_end, and use vprintf.

parsing of args is OK at the first function (e.g. if I cut & paste the
va_arg and printf part to the first function), but garbage is printed in
the second function.

didn't your compiler whine? if not you need to increase the warning level,
and if it did you needed to pay attention to what it said.