xvasprintf
xvasprintf(&msg, fmt2, args);
xvasprintf(&tmp1, fmt, ap);
xvasprintf(&s, fmt, ap);
xvasprintf(&prompt, fmt, args);
xvasprintf(&msg, fmt, args);
xvasprintf(&msg, fmt, ap);
xvasprintf(&msg, fmt, ap);
i = xvasprintf(ret, fmt, ap);
int xvasprintf(char **, const char *, va_list)