Setting NULL causes lag with [MAX_STRING_LENGTH] = {'\0'}; - c++

Question

I thought it would be a good best practice to search thru my code for any references like ..
char buf[MAX_STRING_LENGTH];
... and replace them with ...
char buf[MAX_STRING_LENGTH] = {'\0'};
Doing a search in the code I have a number that are set to null (around 239) and others that are not (1,116).
When I replaced the remaining 1,116 instances with char buf[MAX_STRING_LENGTH] = {'\0'}; and pushed the code live the game was noticeably laggy.
Reverting the change removed the lag.
Can someone explain why setting these to null would cause the game to lag while running?
Example code setting to Null
void do_olist(Character *ch, char *argument, int cmd)
{
int header = 1;
int type = -1;
int wear_bit = -1;
int i = 0;
int inclusive;
int zone = -1;
int yes_key1 = 0;
int yes_key2 = 0;
int yes_key3 = 0;
int count = 0;
Object *obj;
bool found = false;
char key1 [MAX_STRING_LENGTH] = {'\0'};
char key2 [MAX_STRING_LENGTH] = {'\0'};
char key3 [MAX_STRING_LENGTH] = {'\0'};
char buf [MAX_STRING_LENGTH];
argument = one_argument(argument, buf);
if (!*buf)
{
ch->send("Selection Parameters:\n\n");
ch->send(" +/-<object keyword> Include/exclude object keyword.\n");
ch->send(" <zone> Objects from zone only.\n");
ch->send(" <item-type> Include items of item-type.\n");
ch->send(" <wear-bits> Include items of wear type.\n");
ch->send("\nExample: olist +sword -rusty weapon 10\n");
ch->send("will only get non-rusty swords of type weapon from zone 10.\n");
return;
}
while (*buf)
{
inclusive = 1;
if (strlen(buf) > 1 && isalpha(*buf) &&
(type = index_lookup(item_types, buf)) != -1)
{
argument = one_argument(argument, buf);
continue;
}
if (strlen(buf) > 1 && isalpha(*buf) &&
(wear_bit = index_lookup(wear_bits, buf)) != -1)
{
argument = one_argument(argument, buf);
continue;
}
if (isdigit(*buf))
{
if ((zone = atoi(buf)) >= MAX_ZONE)
{
ch->send("Zone not in range 0..99\n");
return;
}
argument = one_argument(argument, buf);
continue;
}
switch (*buf)
{
case '-':
inclusive = 0;
case '+':
if (!buf [1])
{
ch->send("Expected keyname after 'k'.\n");
return;
}
if (!*key1)
{
yes_key1 = inclusive;
strcpy(key1, buf + 1);
}
else if (!*key2)
{
yes_key2 = inclusive;
strcpy(key2, buf + 1);
}
else if (*key3)
{
ch->send("Sorry, at most three keywords.\n");
return;
}
else
{
yes_key3 = inclusive;
strcpy(key3, buf + 1);
}
break;
case 'z':
argument = one_argument(argument, buf);
if (!isdigit(*buf) || atoi(buf) >= MAX_ZONE)
{
ch->send("Expected valid zone after 'z'.\n");
return;
}
zone = atoi(buf);
break;
}
argument = one_argument(argument, buf);
}
*b_buf = '\0';
for (obj = full_object_list; obj; obj = obj->lnext)
{
if (zone != -1 && obj->zone != zone)
continue;
if (type != -1 && obj->obj_flags.type_flag != type)
continue;
if (wear_bit != -1)
{
for (i = 0; (*wear_bits[i] != '\n'); i++)
{
if (IS_SET(obj->obj_flags.wear_flags, (1 << i)))
{
if (i != wear_bit)
continue;
else
found = true;
}
}
if (found)
found = false;
else
continue;
}
if (*key1)
{
if (yes_key1 && !strcasestr(const_cast<char*> (obj->getName().c_str()), key1))
continue;
else if (!yes_key1 && strcasestr(const_cast<char*> (obj->getName().c_str()), key1))
continue;
}
if (*key2)
{
if (yes_key2 && !strcasestr(const_cast<char*> (obj->getName().c_str()), key2))
continue;
else if (!yes_key2 && strcasestr(const_cast<char*> (obj->getName().c_str()), key2))
continue;
}
if (*key3)
{
if (yes_key3 && !strcasestr(const_cast<char*> (obj->getName().c_str()), key3))
continue;
else if (!yes_key3 && strcasestr(const_cast<char*> (obj->getName().c_str()), key3))
continue;
}
count++;
if (count < 200)
olist_show(obj, type, header);
header = 0;
}
if (count > 200)
{
sprintf(buf, "You have selected %d objects (too many to print all at once).\n",
count);
ch->send(buf);
//return;
}
else {
sprintf(buf, "You have selected %d objects.\n",
count);
ch->send(buf);
}
page_string(ch->desc, b_buf);
}

Answer 1

I took the advice to replace instances of ...
char buf[MAX_STRING_LENGTH] = {'\0'};
with ...
char buf[MAX_STRING_LENGTH]; *buf = 0;