Very Computer

Hi. I'm attempting to make a variable arguement function using the functions and
tools provided in <stdarg.h> .. Upon reading the man page stdarg (under Linux),
I was able to put together a small function based on their foo() example.

Unfortunately, the switch statement does not work. I can pass "strings",'c',1 ..
to the function and nothing will be printed. I had attempted to get around that
by removing the switch (since I plan to only pass strings). However, a version
such as this would print a blank line followed by unallocated memory:

void food(char *fmt, ...){
  va_list ap;
  char *s,buf[BUFSIZ+1];

  va_start(ap, fmt);
  while (*fmt++){
    s = va_arg(ap, char *);
    printf("%s\n",s);

  }
  va_end(ap);

Quote:}

Quote:>Unfortunately, the switch statement does not work. I can pass
>"strings",'c',1 .. to the function and nothing will be printed. I had
>attempted to get around that by removing the switch (since I plan to
>only pass strings). However, a version such as this would print a blank
>line followed by unallocated memory:
>void food(char *fmt, ...){
>  va_list ap;
>  char *s,buf[BUFSIZ+1];

>  va_start(ap, fmt);
>  while (*fmt++){
>    s = va_arg(ap, char *);
>    printf("%s\n",s);

>  }
>  va_end(ap);
>}
>In some cases, that example would even seg fault after printing the
>line of strings I sent it. Another note, it would not print the first string
>either.

Your are telling the function food() that the number of arguments being
passed in is equal to the length of first string passed in.  You are then
printing out those other string arguments.  So, a typical way to use food()
would be:

  food ("abc", "one", "two", "three");
  food ("abcd", "one", "two", "three", "four");
  food ("hi", "hello", "world");

The behavior of your program becomes unpredictable if you pass in things
that are different from "char *" types, since that is what you are
expecting to receive according to your while loop.  Moreover, if the
number of strings you pass in not greater than the length of the first
string, then problems will also result.

--

http://www.cs.wustl.edu/~jxh/        Washington University in Saint Louis

Quote:>>>>>>>>>>>>> I use *SpamBeGone* <URL:http://www.internz.com/SpamBeGone/>

Hi / Salut.

Sorry for my poor English...

The right code to calling food is :

                food ("abc", "one", "two", "three", NULL);

Without the NULL at end program's making a good corefile !
The for-loop in food is stopping when it's reads a NULL in the stack.
If you're lucky, the program found a NULL...

A printf-like version of food :

void food(char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  vprintf(fmt, ap);
  va_end(ap);

Quote:}

Quote:>Hi. I'm attempting to make a variable arguement function using the
functions and
>tools provided in <stdarg.h> .. Upon reading the man page stdarg (under
Linux),
>I was able to put together a small function based on their foo() example.

>Unfortunately, the switch statement does not work. I can pass
"strings",'c',1 ..
>to the function and nothing will be printed. I had attempted to get around
that
>by removing the switch (since I plan to only pass strings). However, a
version
>such as this would print a blank line followed by unallocated memory:

>void food(char *fmt, ...){
>  va_list ap;
>  char *s,buf[BUFSIZ+1];

>  va_start(ap, fmt);
>  while (*fmt++){
>    s = va_arg(ap, char *);
>    printf("%s\n",s);

>  }
>  va_end(ap);
>}

>In some cases, that example would even seg fault after printing the
>line of strings I sent it. Another note, it would not print the first
string
>either.