second parameter of `va_start' not last named argument

second parameter of `va_start' not last named argument

[Antonio Coralles]

is there a way to prevent this gcc warning?
in a code similar to

void foo(const std::string& format, ...);

i determine the neccessary number of arguments by counting the 
occurences of "%s" in format,
similar to printf. therefore, there is no need for the caller to pass 
the number of arguments as a second
argument.

thanks
             Antonio

Re: second parameter of `va_start' not last named argument

[Ian Lance Taylor]

Antonio Coralles <noche.suapie@reflex.at> writes:

> is there a way to prevent this gcc warning?
> in a code similar to
> 
> void foo(const std::string& format, ...);
> 
> i determine the neccessary number of arguments by counting the
> occurences of "%s" in format,
> similar to printf. therefore, there is no need for the caller to pass
> the number of arguments as a second
> argument.

If you want help, you will need to post a complete test case.
Specifically, how are you calling va_start?  When you call va_start,
you must pass it the last named argument in the function.  Any other
usage is invalid.

Ian

Re: second parameter of `va_start' not last named argument

[corey taylor]

Exactly, you know the number and so you provide the value to va_start.
 The user calling foo does not provide this.

corey


On Fri, 25 Mar 2005 02:19:06 +0100, Antonio Coralles
<noche.suapie@reflex.at> wrote:
> is there a way to prevent this gcc warning?
> in a code similar to
> 
> void foo(const std::string& format, ...);
> 
> i determine the neccessary number of arguments by counting the
> occurences of "%s" in format,
> similar to printf. therefore, there is no need for the caller to pass
> the number of arguments as a second
> argument.
> 
> thanks
>              Antonio
>

Re: second parameter of `va_start' not last named argument

[Antonio Coralles]

Ian Lance Taylor wrote:

> Antonio Coralles <noche.suapie@reflex.at <mailto:>> writes:
>
>> is there a way to prevent this gcc warning?
>> in a code similar to
>>
>> void foo(const std::string& format, ...);
>>
>> i determine the neccessary number of arguments by counting the
>> occurences of "%s" in format,
>> similar to printf. therefore, there is no need for the caller to pass
>> the number of arguments as a second
>> argument.
>
> If you want help, you will need to post a complete test case.
> Specifically, how are you calling va_start?  When you call va_start,
> you must pass it the last named argument in the function.  Any other
> usage is invalid.
>
> Ian

Here is a test case:

the source looks like this:

void foo(const std::string& format, ...)
{
    unsigned num = string_count("%s", format); // counts how often "%s"
    occurs in format
    va_list p_arg;
    va_start(p_arg, num);
    for(; num > 0; --num)
    {
       const char* arg = va_arg(p_arg, const char*)
       // ... do something with the acquired string
    }
    // ...
}

as i said, the function works similar to printf, and in printf there's no
second parameter specifying the length of the argument list...

antonio

Re: second parameter of `va_start' not last named argument

[Ian Lance Taylor]

Antonio Coralles <noche.suapie@reflex.at> writes:

> void foo(const std::string& format, ...)
> {
>     unsigned num = string_count("%s", format); // counts how often "%s"
>     occurs in format
>     va_list p_arg;
>     va_start(p_arg, num);
>     for(; num > 0; --num)
>     {
>        const char* arg = va_arg(p_arg, const char*)
>        // ... do something with the acquired string
>     }
>     // ...
> }
> 
> as i said, the function works similar to printf, and in printf there's no
> second parameter specifying the length of the argument list...

It should be va_start (p_arg, format).  va_start should always use the
last named parameter.  Nothing else makes sense.

Ian