stdarg problems

[nariknahom]

Hi,

Can someone tell me what is wrong with the below program?
-------------------------------------------
int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is
working." );
return 0;
}

void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);

while (msg != 0 )
{
cout<< msg<<endl;
msg = va_arg(ap, const char *);
}
va_end(ap);

}
--------------------------------------------

the ouput is
------------------------------------------
testing stdarg.
it is working
if it is working.

UH??AWAVAUATSH? ?8H?E?
------------------------------------------

Thanks,
NarikNahom

[Obnoxious User]

On Sun, 01 Jul 2007 15:50:50 +0000, nariknahom wrote:

Hi,

Can someone tell me what is wrong with the below program?
-------------------------------------------
int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is
working." );
return 0;
}

void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);

while (msg != 0 )
{
cout<< msg<<endl;
msg = va_arg(ap, const char *);
}
va_end(ap);

}
--------------------------------------------

the ouput is
------------------------------------------
testing stdarg.
it is working
if it is working.

UH??AWAVAUATSH? ?8H?E?
------------------------------------------

Cleaned up and compilable version of your code.

#include <cstdarg>
#include <iostream>

void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);
while (msg != 0 )
{
std::cout<< msg<<std::endl;
msg = va_arg(ap, const char *);
}
va_end(ap);
}

int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is working.",0 );
return 0;
}

--
Obnoxious User

[Obnoxious User]

On Sun, 01 Jul 2007 15:50:50 +0000, nariknahom wrote:

>
void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);

while (msg != 0 )
{
cout<< msg<<endl;
msg = va_arg(ap, const char *);
}
va_end(ap);

}

You need to know how many arguments you can parse. Your
code is stepping outside its proper context and into
uncharted memory, thus printing weird stuff.

http://www.cppreference.com/stdother/va_arg.html

--
Obnoxious User

[Robert Bauck Hamar]

Obnoxious User wrote:

On Sun, 01 Jul 2007 15:50:50 +0000, nariknahom wrote:

>Hi,

Can someone tell me what is wrong with the below program?
-------------------------------------------
int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is
working." );
return 0;
}

void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);

while (msg != 0 )
{
cout<< msg<<endl;
msg = va_arg(ap, const char *);
}
va_end(ap);

}
--------------------------------------------

the ouput is
------------------------------------------
testing stdarg.
it is working
if it is working.

UH??AWAVAUATSH ??8H?E?
------------------------------------------

Cleaned up and compilable version of your code.

#include <cstdarg>
#include <iostream>

void f1(bool condition, const char * msg,...)
{
va_list ap;
va_start(ap, msg);
while (msg != 0 )
{
std::cout<< msg<<std::endl;
msg = va_arg(ap, const char *);
}
va_end(ap);
}

int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is working.",0 );

I believe this should be

f1( 25 50,"testing stdarg. ", "it is working", "if it is working.",
static_cast<con st char*>(0) );

To make it guaranteed to work. Variable argument functions are mine fields.

The reason is that you must use the same type in va_arg as in the call, and
also because the integer 0 is not required to have the same binary
representation as a null pointer.

return 0;
}

--
rbh

[Rolf Magnus]

na********@gmai l.com wrote:

Hi,

Can someone tell me what is wrong with the below program?

This:

while (msg != 0 )

checks for a null argument, but with:

f1( 25 50,"testing stdarg. ", "it is working", "if it is
working." );

you never supplied one, so your function can't find the end of your argument
list.

[aradhika_c]

On Jul 1, 8:50 am, narikna...@gmai l.com wrote:

Hi,

Can someone tell me what is wrong with the below program?
-------------------------------------------
int main()
{
f1( 25 50,"testing stdarg. ", "it is working", "if it is
working." );
return 0;

}

void f1(bool condition, constchar* msg,...)
{
va_list ap;
va_start(ap, msg);

while (msg != 0 )
{
cout<< msg<<endl;
msg =va_arg(ap, constchar*);
}
va_end(ap);

}

--------------------------------------------

the ouput is
------------------------------------------
testing stdarg.
it is working
if it is working.

UH??AWAVAUATSH? ?8H?E?
------------------------------------------

Thanks,
NarikNahom

Why don't you try msg != NULL and put , NULL as 4th unnamed argumnent
in the function call in the main function?

[nariknahom]

So you have to always provide a NULL as the last argument. I thought
the compiler took care of it.
Shouldnt the compiler already know that?

[Ron Natalie]

ar********@yaho o.com wrote:

>
Why don't you try msg != NULL and put , NULL as 4th unnamed argumnent
in the function call in the main function?

As others pointed out, NULL is an integral constant expression. There's
no guarantee that it can be retrieved by va_arg as a pointer.

He needs to use a null pointer value of type const char*.

[Ron Natalie]

na********@gmai l.com wrote:

So you have to always provide a NULL as the last argument. I thought
the compiler took care of it.

No, the compiler has no clue what you want to do. stdarg is pretty
lame and owes it's history to some very early C implementations of
printf.

Shouldnt the compiler already know that?

Known what?

While in C++ the fact that the function is declared with ... in the
parameter list means that it should be able to pass information like
the actual types and the number of args, historical compatibility with
loosy-goosy typed C functions precludes this.

[nariknahom]

Is the ellipsis( ... ) a part of C/C++ or stdarg.h? If its part of the
C/C++, then shouldnt the compiler know where the end of the arguments
is and automatically insert a NULL? Maybe this is not how C/C++ is
designed but what are the disadvantages if it is so?