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I've been studing the way to have a more useful strcat function and I
realized that I need more than one argument to handle at a time, and
also a way to resize the pointer automatically so I can forget the
memory handling problem.

So I constructed a new xstrcat function but, although works pretty
well in most environments, I discover that it works erratically when I
try to add the result var on the list of strings to add (i mean if I
do a xstrcat(&tmp, tmp, NULL)), so I send this to the community to see
if someone with more experience than me can help.
Cheers,
Leo

char *
xstrcat (char **dest, char *str, ...)
{
va_list va;
size_t length = 0;
char *ptr, *tmp;

if (!str)
return (char *) NULL;

length += strlen (str);

va_start (va, str);
while ((tmp = va_arg (va, char *)))
length += strlen (tmp);
va_end (va);

if (!*dest)
*dest = malloc (length + 1);
else
*dest = realloc (*dest, (length + 1));

if (!dest)
return (char *) NULL;

ptr = *dest;

for (tmp = str; *tmp; tmp++)
*ptr++ = *tmp;

va_start (va, str);
while ((tmp = va_arg (va, char *)))
{
while (*tmp)
*ptr++ = *tmp++;
}
va_end (va);
*ptr = '\0';
return *dest;
}

(Leonardo Javier Belén) writes:

> So I constructed a new xstrcat function but, although works pretty
> well in most environments, I discover that it works erratically when I
> try to add the result var on the list of strings to add (i mean if I
> do a xstrcat(&tmp, tmp, NULL)), so I send this to the community to see
> if someone with more experience than me can help.

> char *
> xstrcat (char **dest, char *str, ...)
> {
> va_list va;
> size_t length = 0;
> char *ptr, *tmp;
>
> if (!str)
> return (char *) NULL;

The cast is gratuitous.

> length += strlen (str);
>
> va_start (va, str);
> while ((tmp = va_arg (va, char *)))
> length += strlen (tmp);
> va_end (va);
>
> if (!*dest)
> *dest = malloc (length + 1);
> else
> *dest = realloc (*dest, (length + 1));

1. realloc() acts like malloc() when the first argument is a null
pointer, so there's no need to switch to malloc() for that
case.

2. If realloc() fails, you probably just leaked memory, because
you overwrote the original pointer.

> if (!dest)

This does not test what you think it tests. If allocation
failed, *dest will be a null pointer, not dest.

> return (char *) NULL;

Gratuitous cast.

> ptr = *dest;
>
> for (tmp = str; *tmp; tmp++)
> *ptr++ = *tmp;
> va_start (va, str);
> while ((tmp = va_arg (va, char *)))
> {
> while (*tmp)
> *ptr++ = *tmp++;
> }
> va_end (va);
> *ptr = '\0';

The rest of this looks okay, though I'd prefer strcpy() followed
by strchr() over explicit loops.

> return *dest;
> }

--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv wxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p[i]\
);}return 0;}