C++ operator?

[kageb0shi]

I have a little bit of experience in C++, but evidently not enough. Digging around in Mangos source I keep seeing this operator(?)

->

context example:

                if(m_spellInfo->SpellIconID == 1648)        // Execute
               {
                   if(!m_targets.getUnitTarget() || m_targets.getUnitTarget()->GetHealth() > m_targets.getUnitTarget()->GetMaxHealth()*0.2)
                       return SPELL_FAILED_BAD_TARGETS;
               }

I recognize all the operators in that example, ! = NOT, || = OR, == equals to, > greater than, GetHealth() function, * multiply, ; end of statement, except I do not know what -> is

I have done google searches, but no relevant results.

[VladimirMangos]

a -> b is same (in most cases) as (*a).b at least for built-in types...

if 'a' is pointer to some object or structure with field 'b' then a -> b will return value of (in fact reference to) field 'b' od structure 'a'.

[kageb0shi]

ah I see. Thank you so much for helping me understand that.

just as, for example

int a[5] = { 3, 4, 8, 9}

int b = 2;

int value = a;

value would equal 8.

I understand to a certain degree. Though I am certain a pointer is more complex than an array. I had not yet covered pointers in my C++ class. next semester i think I will see it.

[Patman128]

A pointer is sort of what it sounds like: a pointer to a location in memory. That location can be anything. If it is an instance of class, -> can be used to call member variables or functions from that instance of the class.

It sounds much more difficult than it actually is. Just remember than if you have a pointer variable, like Player * player, and you want to call a function on it, you would use player->function().

[jolan]

pointers are much more efficient to move around.

function doSomething(Player thePlayer); // will copy the Player struct each time it is called, will delete it when it returns, will not modify the original Player if the function modify (or call a member function modifying) thePlayer

function doSomething(Player* thePlayer); // none of the above

so the second version is faster and use less memory.

[kageb0shi]

pointers are much more efficient to move around.

function doSomething(Player thePlayer); // will copy the Player struct each time it is called, will delete it when it returns, will not modify the original Player if the function modify (or call a member function modifying) thePlayer

function doSomething(Player* thePlayer); // none of the above

so the second version is faster and use less memory.

ah I see. Instead of passing by value (which makes a copy if I understand it) it is actually passing the variable, so then the original variable is modified and not some copy. I see!

[pelle]

as we are here, i'd like to know _what_ pointer whe should use for exemple on spellauras.cpp.

i understood that m_taget is the taget and caster is the player who do something but...

can i use that?

for exemple if i want the rogue autocast something on him (in this case the find weakness buff) , can i use

if (caster->HasSpell(31242)) //if has talent

caster->CastSpell(caster, 31238, true, NULL, NULL, GetCasterGUID()); //cast on him the spell

thanks for asnwer

[freghar]

Pointers are probably the most powerful thing in C and pretty important in C++ as well. That means there's a LOT of tutorials explaining pointers from every possible angle of explanation.

IMHO the easiest way of understanding pointers is to realize what they actually are. A four-byte (on 32bit machines) or eight-byte (64bit) locations in memory, containing a destination address they're pointing to. Nothing more. All those types of pointers (like int*, Player* and so on) only allows you to easily manipulate with the destination target. A pointer has still 4 (8) bytes. That's why you actually can use a void* and then typecast it like ((Player *)my_void_ptr)->GetName().

Pointers are simple once you understand how they work.

edit: just an example I used some year back in a Linux kernel module;

char *buffer;
__u16 ip_csum;
__u16 tcp_csum;

buffer = skb_network_header(skb);
ip_csum = ((struct iphdr *)buffer)->check;
tcp_csum = ((struct tcphdr *)buffer+sizeof(struct iphdr))->check;

(I ofc omitted a lots of checks and such)

This way I'm able to get both IPv4 and TCP checksums from a packet using only one generic *buffer pointer (there could also be a check for IPv4/6 and doing all the work with only "buffer").

In practice it's better to use more abstraction layers.